**SiC (422)**

**Si (331)**

**Si (511)**

**Si (531) Si (matrix)**

In the layer SiC0.4 the presence of polycrystalline phases of SiC and Si after implantation and annealing at 1000, 1100 and 1250°C are revealed. High intensity peaks of SiC after annealing at 1100ºC (Fig. 9a) indicates on intensive process of crystallization of β-SiC due to lower content of stable clusters in comparison with the layers SiC1.4, SiC0.95 and SiC0.7. High amplitude of β-SiC peaks after annealing at 1250оС confirms this assertion. In diffraction pattern of SiC0.12 layer after implantation a broad diffuse line of amorphous silicon Si(111) (θ = 14.3º) is observed (Fig.10a). After annealing at 800ºC a narrowing of this line, at 900ºC a sharp narrowing of the line Si(111) and the appearance of Si(220) and Si(311) lines of polycrystalline Si phase, as well as two weak lines of β-SiC, at 1250ºC - a decrease of the integrated intensity of Si lines, are observed.

Fig. 9. X-ray diffraction patterns of the SiC0.4 layer annealed for 30 min at (a) 1100ºС and (b) 1250°C.

The implantation of carbon causes the formation of weakly ordered set of randomly oriented Si regions of size ~1.5 nm. Temperature dependence of the average crystallite size Si (Fig. 11a, curve 1) and SiC (curve 2) in plane (111) shows that at low temperatures the curve 1 is characterized by slow growth in the size of weakly ordered Si nanocrystals. Their transformation into well ordered Si crystallites at 800ºC is taken place. Average size of Si crystallites is 47 nm after annealing at 1250ºC. The formation of β-SiC crystallites prevent a complete recrystallization of layer at this temperature.

The integrated intensity curve of Si(111) line, which is proportional to the phase volume, has three sections in the temperature ranges of 20– 800ºC, 800−900ºC and 900−1250ºC (Fig. 11b). In the range of 20-800ºC Iint decreases, indicating a decrease in the total volume of nanocrystals Si, although their sizes increase up to 2.2 nm. The growth of weak ordered Si crystallites is accompanied by the displacement of carbon atoms in the surrounding space, which no longer contribute to the intensity of the Si (111) line due to increased concentration of carbon. In addition, there is recrystallization of silicon near the substrate. It is assumed that, after annealing at 800ºC (Figs. 11b and 12) approximately k800 ≈ [Iint(800ºС)/Iint(20ºС)]×100% = 72% of silicon atoms in the layer is incorporated into crystallites of Si. The remaining atoms of Si (28%) are in an amorphous mixture of Si and C atoms, or reunited with the substrate.

In the layer SiC0.4 the presence of polycrystalline phases of SiC and Si after implantation and annealing at 1000, 1100 and 1250°C are revealed. High intensity peaks of SiC after annealing at 1100ºC (Fig. 9a) indicates on intensive process of crystallization of β-SiC due to lower content of stable clusters in comparison with the layers SiC1.4, SiC0.95 and SiC0.7. High amplitude of β-SiC peaks after annealing at 1250оС confirms this assertion. In diffraction pattern of SiC0.12 layer after implantation a broad diffuse line of amorphous silicon Si(111) (θ = 14.3º) is observed (Fig.10a). After annealing at 800ºC a narrowing of this line, at 900ºC a sharp narrowing of the line Si(111) and the appearance of Si(220) and Si(311) lines of polycrystalline Si phase, as well as two weak lines of β-SiC, at 1250ºC - a decrease of the

**0,4**

**10 20 30 40** θ**, degree**

**Si**

**С (111)**

Si (substrate)

**Si (311)**

**Si**

**Si**

**С (311)**

**С (220)**

**Si (220)**

**0,6**

**0,8**

**1,0**

**I, arb.un.**

Fig. 9. X-ray diffraction patterns of the SiC0.4 layer annealed for 30 min at (a) 1100ºС and (b)

The implantation of carbon causes the formation of weakly ordered set of randomly oriented Si regions of size ~1.5 nm. Temperature dependence of the average crystallite size Si (Fig. 11a, curve 1) and SiC (curve 2) in plane (111) shows that at low temperatures the curve 1 is characterized by slow growth in the size of weakly ordered Si nanocrystals. Their transformation into well ordered Si crystallites at 800ºC is taken place. Average size of Si crystallites is 47 nm after annealing at 1250ºC. The formation of β-SiC crystallites prevent a

The integrated intensity curve of Si(111) line, which is proportional to the phase volume, has three sections in the temperature ranges of 20– 800ºC, 800−900ºC and 900−1250ºC (Fig. 11b). In the range of 20-800ºC Iint decreases, indicating a decrease in the total volume of nanocrystals Si, although their sizes increase up to 2.2 nm. The growth of weak ordered Si crystallites is accompanied by the displacement of carbon atoms in the surrounding space, which no longer contribute to the intensity of the Si (111) line due to increased concentration of carbon. In addition, there is recrystallization of silicon near the substrate. It is assumed that, after annealing at 800ºC (Figs. 11b and 12) approximately k800 ≈ [Iint(800ºС)/Iint(20ºС)]×100% = 72% of silicon atoms in the layer is incorporated into crystallites of Si. The remaining atoms of Si (28%) are in an amorphous mixture of Si and

**Si**

**С (220)**

**5 15 25 35 45** θ**, degree**

**SiC (111)**

**Si (220)**

**Si (311)**

**1,2**

**Si (111)**

**b)**

**1,4**

**1,6**

integrated intensity of Si lines, are observed.

**Si (111)**

complete recrystallization of layer at this temperature.

C atoms, or reunited with the substrate.

**а)**

**0,1**

**0,3**

**0,5**

**0,7**

**I, arb.un.**

1250°C.

**0,9**

**1,1**

**1,3**

Fig. 10. X-ray diffraction patterns of the SiC0.12 layer (a) before and after annealing for 30 min at (b) 1100ºС and (c) 1250°C.

Fig. 11. Average sizes (a) of Si and SiC crystallites in the (111) plane and (b) the integrated intensities of the Si(111) and SiC(111) lines after implantation of carbon ions in silicon and annealing. 1 − Si (for layer SiC**0.03**), 2 − Si (for layer SiC**0.12**), 3 − SiС (for layer SiC**0.12**).

The Formation of Silicon Carbide in the SiCx Layers

characteristic of crystalline phases of Si and SiC.

**Si (111) .**

**Si**

**Si**

**С (200)**

**.**

**С (111) .**

**0,25**

recrystallization near the substrate.

**0,35**

**0,45**

**0,55**

**I, arb.units**

**0,65**

**0,75**

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 83

two grains is taken place, if it is accompanied by a gain in energy which is greater than its costs for the destruction of the crystallites. In this case, the redistribution of atoms with a change in chemical bond lengths and angles between them is taken place, in order to select a more favorable energy state, which is the states with tetrahedral oriented bonds,

**10 30 50 70 90**

The X-ray diffraction results are in accordance with the data of Auger electron spectroscopy, whereby the concentration of carbon atoms in a layer is NC/NSi = 0.12/1 (Fig. 2). Then the maximum possible ratio of atoms, forming part of SiC and Si, will be: NSiC/NSi = 0.24/0.88 = 0.27. As seen in Figure 11b, the maximum quantity of poly-SiC, obtained at 1250ºC, was Iint(SiC) = 0.040, and poly-Si was Iint(Si) = 0.131 at 900ºС, i.e., Iint(SiC)/Iint(Si) = 0.040/0.131 =

Similar features are observed for a layer with a lower carbon concentration SiC0.03. Immediately after the implantation the same broad diffuse line of amorphous silicon Si(111) at θ = 14.3º is observed (Fig. 14). Increase of annealing temperature above 800ºC causes narrowing of this line, increasing the number and amplitude of the line intensity which reaches its maximum at 1100ºC. However, in the X-ray diffraction patterns of SiC0.03 layer no lines of polycrystalline silicon carbide in the whole temperature range are observed due to insufficient concentration of the carbon atoms to form a large number of SiC crystallites. Annealing at temperatures above 1100º C reduces the intensity of Si lines and results their

For comparison, in Table 3 the grain sizes of silicon and silicon carbide in plane (111) in layers Si(111) and β-SiС(111) are given. Dimensions of weakly ordered regions in SiC0.03 layer, contributing to the intensity of the Si(111) line, exceed the same values for SiC0.12. This is associated with a lower concentration of carbon and larger volume of Si regions with extremely low concentrations of carbon. At temperatures of 1200 and 1250ºC a decrease in the average crystallite size up to 10 nm is observed, which is associated with the process of

Fig. 13. X-ray diffraction pattern of the SiC0.12 layer after annealing at 1400°C for 30 min.

0.30, which is comparable with the data of Auger electron spectroscopy.

disappearance after annealing at 1250ºC due to recrystallization of the layer.

**Si (220) .**

**Si**

**Si**

**С (311) .**

**С (220) .**

**2**θ**, degree**

Fig. 12 schematically shows the variation of the structure of the layer, its phase composition and phase volume, as well as the average grain size as a function of annealing temperature (a) and scheme of Si and SiC crystallite formation in this layer (b). The diagram is based on the curves in Fig. 11a, b for SiC0.12. Regions "amorphous Si-C mixture" and "c-Si" are formed adhering to the relation: "amorphous Si-C mixture" + "c-Si" = 100% − ("poly-SiC" + "poly-Si"+"amorphous -Si").

Fig. 12. Crystallization of the SiC0.12 layer: (a) the phase volumes at various annealing temperatures and (b) the formation of crystalline Si and SiC crystallites in the temperature range 900−1000°C.

In the range of 800−900°C the increase in both size crystallites Si (from 2.2 to 4.7 nm) and the volume of polycrystalline phase of Si (Fig. 11a and 12) is observed. This is due to the formation of SiC crystallites at 900°C in the regions of carbon accumulation and the joining of excess silicon atoms to Si crystallites. So, k is increased: k900 ≈ 82%. This leads to a decrease in Si−C-mixture volume (Fig. 12). After annealing at 1000ºC and 1250ºC, an increase in the phase volume and crystallite sizes of β-SiC as well as a decrease in k due to recrystallization of regions near the Si substrate, are taken place: k1000 ≈ 73% and k1250 ≈ 46%. Si crystallite sizes increased almost 10 times (up to 47 nm). Probably, there is destruction of defective silicon crystallites and the uniting of their atoms into crystallites with a perfect structure or with the substrate. As can be seen from the diagram, after annealing at 1200°C in the layer SiC0.12 ~50% of silicon atoms are incorporated into Si crystallites with an average size of 25 nm, 25% of Si atoms are included into β-SiC crystallite with size of 5 nm and 25% are joined with Si substrate. Since the unit cell volume for Si is twice more than the cell volume for SiC, the volume of the surface layer of Si after implantation and annealing of carbon should not change appreciably, and the above relations can be regarded as a volume ratio of phases.

During annealing at 1400ºC there is the destruction of most of the silicon crystallites and connection of their atoms to the substrate. The intensity of the lines Si was significantly lower than the intensities of β-SiC lines (Fig. 13). It is assumed that recrystallized Si layer with ingrained in him crystallites of β-SiC and Si on a silicon substrate was obtained.

During a growth of the crystallite size is manifested basic thermodynamic law: in an isolated system, the processes occurring with increasing free energy, is prohibited. Combining the

Fig. 12 schematically shows the variation of the structure of the layer, its phase composition and phase volume, as well as the average grain size as a function of annealing temperature (a) and scheme of Si and SiC crystallite formation in this layer (b). The diagram is based on the curves in Fig. 11a, b for SiC0.12. Regions "amorphous Si-C mixture" and "c-Si" are formed adhering to the relation: "amorphous Si-C mixture" + "c-Si" = 100% − ("poly-SiC" + "poly-

Fig. 12. Crystallization of the SiC0.12 layer: (a) the phase volumes at various annealing temperatures and (b) the formation of crystalline Si and SiC crystallites in the temperature

with ingrained in him crystallites of β-SiC and Si on a silicon substrate was obtained.

During a growth of the crystallite size is manifested basic thermodynamic law: in an isolated system, the processes occurring with increasing free energy, is prohibited. Combining the

In the range of 800−900°C the increase in both size crystallites Si (from 2.2 to 4.7 nm) and the volume of polycrystalline phase of Si (Fig. 11a and 12) is observed. This is due to the formation of SiC crystallites at 900°C in the regions of carbon accumulation and the joining of excess silicon atoms to Si crystallites. So, k is increased: k900 ≈ 82%. This leads to a decrease in Si−C-mixture volume (Fig. 12). After annealing at 1000ºC and 1250ºC, an increase in the phase volume and crystallite sizes of β-SiC as well as a decrease in k due to recrystallization of regions near the Si substrate, are taken place: k1000 ≈ 73% and k1250 ≈ 46%. Si crystallite sizes increased almost 10 times (up to 47 nm). Probably, there is destruction of defective silicon crystallites and the uniting of their atoms into crystallites with a perfect structure or with the substrate. As can be seen from the diagram, after annealing at 1200°C in the layer SiC0.12 ~50% of silicon atoms are incorporated into Si crystallites with an average size of 25 nm, 25% of Si atoms are included into β-SiC crystallite with size of 5 nm and 25% are joined with Si substrate. Since the unit cell volume for Si is twice more than the cell volume for SiC, the volume of the surface layer of Si after implantation and annealing of carbon should not change appreciably, and the above relations can be regarded as a volume ratio of phases. During annealing at 1400ºC there is the destruction of most of the silicon crystallites and connection of their atoms to the substrate. The intensity of the lines Si was significantly lower than the intensities of β-SiC lines (Fig. 13). It is assumed that recrystallized Si layer

Si"+"amorphous -Si").

range 900−1000°C.

two grains is taken place, if it is accompanied by a gain in energy which is greater than its costs for the destruction of the crystallites. In this case, the redistribution of atoms with a change in chemical bond lengths and angles between them is taken place, in order to select a more favorable energy state, which is the states with tetrahedral oriented bonds, characteristic of crystalline phases of Si and SiC.

Fig. 13. X-ray diffraction pattern of the SiC0.12 layer after annealing at 1400°C for 30 min.

The X-ray diffraction results are in accordance with the data of Auger electron spectroscopy, whereby the concentration of carbon atoms in a layer is NC/NSi = 0.12/1 (Fig. 2). Then the maximum possible ratio of atoms, forming part of SiC and Si, will be: NSiC/NSi = 0.24/0.88 = 0.27. As seen in Figure 11b, the maximum quantity of poly-SiC, obtained at 1250ºC, was Iint(SiC) = 0.040, and poly-Si was Iint(Si) = 0.131 at 900ºС, i.e., Iint(SiC)/Iint(Si) = 0.040/0.131 = 0.30, which is comparable with the data of Auger electron spectroscopy.

Similar features are observed for a layer with a lower carbon concentration SiC0.03. Immediately after the implantation the same broad diffuse line of amorphous silicon Si(111) at θ = 14.3º is observed (Fig. 14). Increase of annealing temperature above 800ºC causes narrowing of this line, increasing the number and amplitude of the line intensity which reaches its maximum at 1100ºC. However, in the X-ray diffraction patterns of SiC0.03 layer no lines of polycrystalline silicon carbide in the whole temperature range are observed due to insufficient concentration of the carbon atoms to form a large number of SiC crystallites. Annealing at temperatures above 1100º C reduces the intensity of Si lines and results their disappearance after annealing at 1250ºC due to recrystallization of the layer.

For comparison, in Table 3 the grain sizes of silicon and silicon carbide in plane (111) in layers Si(111) and β-SiС(111) are given. Dimensions of weakly ordered regions in SiC0.03 layer, contributing to the intensity of the Si(111) line, exceed the same values for SiC0.12. This is associated with a lower concentration of carbon and larger volume of Si regions with extremely low concentrations of carbon. At temperatures of 1200 and 1250ºC a decrease in the average crystallite size up to 10 nm is observed, which is associated with the process of recrystallization near the substrate.

The Formation of Silicon Carbide in the SiCx Layers

**3.4 Investigations by infrared spectroscopy**

**IR transmittance,**

**67**

**87**

**65**

**85**

**%**

**17**

**87**

**23**

**83**

**72**

**22**

**68**

**38**

**75**

**45**

**58 63**

**83**

**78**

**63**

**83**

**65 66**

**85**

**86**

temperature range 200−1400°C were measured (Figs. 16−21).

**a) sample**

**90o**

T1

**IR-beam**

**500<PHONE_NUMBER> Wave number, cm-1**

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 85

The influence of carbon concentration in the SiCx layers and annealing temperature on the parameters of the spectra of infrared spectroscopy was investigated. For this purpose, using two-beam infrared spectrometer UR-20 the IR transmission spectra of SiC1.4, SiC0.95, SiC0.7, SiC0.4, SiC0.12 and SiC0.03 layers before and after isochronous annealing in vacuum at

**IR-beam**

**b)**

**59**

**76 56**

**79**

**46**

**66**

**20o C**

Fig. 16. IR transmission spectra of the SiC1.4 layer recorded (a) under normal incidence of IR radiation on the sample and (b) at an angle of 73° to the normal to the sample surface.

**200o C**

**400o C**

**900o C**

**800o C**

**700o C**

**600o C**

**1200o C**

**1100o C**

**1000o C**

**1300o C**

**1400о C**

T2

**78 58**

**82 62**

**78 58**

**76**

**40**

**56**

**60**

**67 37**

**23**

**73**

**16**

**76**

**22**

**72**

**73o 90o**

**sample**

**500<PHONE_NUMBER>**

**-1**

**Wave number, cm**

Fig. 14. X-ray diffraction of SiC0.03 layer after implantation of carbon ions in Si (а) and annealing at 1100°C (b) and 1200°C (c) for 30 min.

Table 3. Average size (ε) of Si- and β-SiC crystallites in SiCx layers

Temperature dependences of the integrated intensity of Si(111) line (Fig. 15) for the SiC0.03 and SiC0.12 layers are similar in nature. A lower carbon concentration in SiC0.03 layer results more intensive decrease in the phase volume of poly-Si at temperatures above 700ºC due to more intensive recrystallization near the substrate. The value of k were: k800 ≈ 40%, k900 ≈ 27%, k1000 ≈ 44%, k1100 ≈ 41%, k1250 ≈ 6%. Growth of k up to 44% at 1000ºC for SiC0.03 layer due to accession of excess silicon atoms from the carbon-rich Si-C-mixture to the Si crystallite is taken place. For a layer SiC0.12, that is observed at a temperature of 100ºC below due to a higher concentration of carbon, therefore the carbon rich region is formed at lower temperatures and does not require significant movements of atoms. Annealing at 1250ºC results in uniting of SiC0.03 layer with single-crystal substrate (K1250×100% = [0,007/0,116]×100% = 6%) and the decrease in the average size of residual crystallites up to 10 nm.

#### **3.4 Investigations by infrared spectroscopy**

84 Silicon Carbide – Materials, Processing and Applications in Electronic Devices

Si (220)

Si (311)

Si (400)

Si (331)

Si (111)

(b)

10 20 30 40 θ, degree

20 2 – 1.1 – – – 700 3 – 1.3 – – – 800 13 – 2 – – –

1000 17 – 5 3 4 3 1100 20 – 7 3.5 4 3

1250 10 – 46 5 9 4.5

Temperature dependences of the integrated intensity of Si(111) line (Fig. 15) for the SiC0.03 and SiC0.12 layers are similar in nature. A lower carbon concentration in SiC0.03 layer results more intensive decrease in the phase volume of poly-Si at temperatures above 700ºC due to more intensive recrystallization near the substrate. The value of k were: k800 ≈ 40%, k900 ≈ 27%, k1000 ≈ 44%, k1100 ≈ 41%, k1250 ≈ 6%. Growth of k up to 44% at 1000ºC for SiC0.03 layer due to accession of excess silicon atoms from the carbon-rich Si-C-mixture to the Si crystallite is taken place. For a layer SiC0.12, that is observed at a temperature of 100ºC below due to a higher concentration of carbon, therefore the carbon rich region is formed at lower temperatures and does not require significant movements of atoms. Annealing at 1250ºC results in uniting of SiC0.03 layer with single-crystal substrate (K1250×100% = [0,007/0,116]×100% = 6%) and the decrease in the average size of residual

ε (nm) SiC0.03 SiC0.12 SiC0.4 Si β-SiC Si β-SiC Si β-SiC

Fig. 14. X-ray diffraction of SiC0.03 layer after implantation of carbon ions in Si (а) and

0.2

900 15 – 4.5 2

1150 27 – 12 4 1200 10 – 25 4.5

Table 3. Average size (ε) of Si- and β-SiC crystallites in SiCx layers

0.6

1.0

1.4

I, arb.un.

Si (matrix)

0.4

Temperature (ºС)

crystallites up to 10 nm.

10 20 30 40 θ, degree

annealing at 1100°C (b) and 1200°C (c) for 30 min.

0.8

1.2

1.6

I, arb.un.

2.0

Si (111)

(a)

2.4

1.8

2.2

0.0

10 20 30 40 θ, degree

0.4

0.8

1.2

I, arb.un.

1.6

Si (111)

(c)

Si (matrix) Si (220)

Si (311)

2.0

The influence of carbon concentration in the SiCx layers and annealing temperature on the parameters of the spectra of infrared spectroscopy was investigated. For this purpose, using two-beam infrared spectrometer UR-20 the IR transmission spectra of SiC1.4, SiC0.95, SiC0.7, SiC0.4, SiC0.12 and SiC0.03 layers before and after isochronous annealing in vacuum at temperature range 200−1400°C were measured (Figs. 16−21).

Fig. 16. IR transmission spectra of the SiC1.4 layer recorded (a) under normal incidence of IR radiation on the sample and (b) at an angle of 73° to the normal to the sample surface.

The Formation of Silicon Carbide in the SiCx Layers

**90o**

 **IR-beam**

a)

**IR transmittance (%)**

**26**

**81**

**76**

**11**

**77**

**27**

**38**

**78**

**90**

**50 59**

**79**

**62**

**82**

**63**

**83 83**

**63**

**85**

**65**

**87**

**67**

**67**

**87**

**500<PHONE_NUMBER> Wave number, cm-1**

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 87

**sample**

 **IR-beam**

б)

**70 40**

**75 55**

**77 57**

**20o C**

Fig. 17. IR transmission spectra of the SiC0.95 layer recorded (a) under normal incidence of IR radiation on the sample and (b) at an angle of 73° to the normal to the sample surface.

**200o C**

**900o C**

**1000o C**

**800o C**

**700o C**

**600o C**

**400o C**

**1200o C**

**1100o C**

**1300o C**

**1400о C**

> **75 55**

> **77 57**

> **77 57**

> **78 58**

> **77 57**

> **80 50**

> **29**

**69**

**14**

**74**

**30**

**70**

**73o 90o**

**sample**

**500<PHONE_NUMBER> Wave number, cm-1**

At respecting certain condition, one can observe not only the transverse optical oscillations of atoms (TO-phonons), as well as longitudinal optical lattice oscillations (LO-phonons). For this purpose, we measured IR transmittance spectra of the implanted layers both at normal incidence of radiation on the sample, and at 73° to the normal to the surface (Figs. 16−21a, b). For a visual comparison of spectra from the SiCх layers in Fig. 22 series of spectra of these layers before and after annealing at 600, 1000 and 1300°C measured at normal incidence of radiation on the sample, are presented. It is seen that among these layers a SiC-peak of the IR transmittance for the SiC0.7 layer has maximum value of amplitude and minimum half-width after annealing at 1300°C. This implies a maximum number of tetrahedral oriented Si–C-bonds and high crystallinity of this layer, although the carbon concentration below the stoichiometric SiC. This phenomenon requires an explanation. For this purpose, an analysis of dependence of SiC-peak parameters on both annealing temperature and concentration of carbon for SiCх layers was carried out.

It is well known that the spectral range 500−1100 cm-1 considered here includes the absorption bands corresponding to valence oscillations (in which the lengths of bonds vary predominantly) of the Si−C, C−C, and C−O-bonds, as well as deformation vibrations (in which the angles between the bonds are changed). As a result of interactions of these oscillations, it is impossible in principle to attribute the absorption band to individual bonds. If we assume that in the ideal case each type of Si−C-bonds corresponds to absorption at a certain frequency or in a narrow frequency interval, it can be concluded from the spectra in Figs. 16−22 that after implantation of carbon into silicon, the contour curve of the IR spectrum covers a large frequency (or wavenumber) range; i.e., the ion implanted layer contains a large number of different types of Si−C-bonds absorbing at different frequencies. Tetrahedral oriented Si−C-bonds with a length of 0.194 nm in crystalline silicon carbide absorb at the frequency corresponding to a wavenumber of 800 cm–1, while the silicon layer amorphized by implantation of carbon ions contains Si−Cbonds with a length larger and smaller than this value and absorb at the frequencies slightly different from 800 cm–1. This may be due to the fact that the stopping particles form a new Si−C-bonds which are not covalent because of variations in their length and in the angles between them. In the implanted amorphous Si−C-layer, one can also expect the presence of shorter double Si=C and triple Si≡C bonds, whose length is much smaller. Among the bonds can be present also the bonds, distances and angles between them (between atoms) are exactly the same as in the crystallite of SiC. For example, Kimura et al. (1981) by electron diffraction observed the crystallites of SiC immediately after implantation. In this case, one can observe non-zero absorption at a frequency of 800 cm-1 after implantation.

In addition, in the implanted layer can be expected the presence of long single bonds, free (dangling) bonds and hybridized Si−C-bonds, resonance and other higher order interactions. If the absorption of double C=C-bonds (1620-1680 cm-1) and the triple C≡Cbonds (2100−2200 cm-1) is beyond the study of the contour curve of the IR spectrum 500−1100 cm-1, but the vibrations of C−C are in the region 900−1100 cm-1. Nevertheless, the contribution to change the contour of the curve in this range and, in particular, to change the peak area will have a decay of single C−C, double C=C, Si=C or Si=Si, and triple C≡C, Si≡C or Si≡Si bonds, because of the formation after their decay of Si−C-bonds absorbing in this range (Silverstein et al., 1977].

At respecting certain condition, one can observe not only the transverse optical oscillations of atoms (TO-phonons), as well as longitudinal optical lattice oscillations (LO-phonons). For this purpose, we measured IR transmittance spectra of the implanted layers both at normal incidence of radiation on the sample, and at 73° to the normal to the surface (Figs. 16−21a, b). For a visual comparison of spectra from the SiCх layers in Fig. 22 series of spectra of these layers before and after annealing at 600, 1000 and 1300°C measured at normal incidence of radiation on the sample, are presented. It is seen that among these layers a SiC-peak of the IR transmittance for the SiC0.7 layer has maximum value of amplitude and minimum half-width after annealing at 1300°C. This implies a maximum number of tetrahedral oriented Si–C-bonds and high crystallinity of this layer, although the carbon concentration below the stoichiometric SiC. This phenomenon requires an explanation. For this purpose, an analysis of dependence of SiC-peak parameters on both annealing temperature and concentration of carbon for

It is well known that the spectral range 500−1100 cm-1 considered here includes the absorption bands corresponding to valence oscillations (in which the lengths of bonds vary predominantly) of the Si−C, C−C, and C−O-bonds, as well as deformation vibrations (in which the angles between the bonds are changed). As a result of interactions of these oscillations, it is impossible in principle to attribute the absorption band to individual bonds. If we assume that in the ideal case each type of Si−C-bonds corresponds to absorption at a certain frequency or in a narrow frequency interval, it can be concluded from the spectra in Figs. 16−22 that after implantation of carbon into silicon, the contour curve of the IR spectrum covers a large frequency (or wavenumber) range; i.e., the ion implanted layer contains a large number of different types of Si−C-bonds absorbing at different frequencies. Tetrahedral oriented Si−C-bonds with a length of 0.194 nm in crystalline silicon carbide absorb at the frequency corresponding to a wavenumber of 800 cm–1, while the silicon layer amorphized by implantation of carbon ions contains Si−Cbonds with a length larger and smaller than this value and absorb at the frequencies slightly different from 800 cm–1. This may be due to the fact that the stopping particles form a new Si−C-bonds which are not covalent because of variations in their length and in the angles between them. In the implanted amorphous Si−C-layer, one can also expect the presence of shorter double Si=C and triple Si≡C bonds, whose length is much smaller. Among the bonds can be present also the bonds, distances and angles between them (between atoms) are exactly the same as in the crystallite of SiC. For example, Kimura et al. (1981) by electron diffraction observed the crystallites of SiC immediately after implantation. In this case, one can observe non-zero absorption at a frequency of 800 cm-1

In addition, in the implanted layer can be expected the presence of long single bonds, free (dangling) bonds and hybridized Si−C-bonds, resonance and other higher order interactions. If the absorption of double C=C-bonds (1620-1680 cm-1) and the triple C≡Cbonds (2100−2200 cm-1) is beyond the study of the contour curve of the IR spectrum 500−1100 cm-1, but the vibrations of C−C are in the region 900−1100 cm-1. Nevertheless, the contribution to change the contour of the curve in this range and, in particular, to change the peak area will have a decay of single C−C, double C=C, Si=C or Si=Si, and triple C≡C, Si≡C or Si≡Si bonds, because of the formation after their decay of Si−C-bonds absorbing in this

SiCх layers was carried out.

after implantation.

range (Silverstein et al., 1977].

Fig. 17. IR transmission spectra of the SiC0.95 layer recorded (a) under normal incidence of IR radiation on the sample and (b) at an angle of 73° to the normal to the sample surface.

The Formation of Silicon Carbide in the SiCx Layers

**o**

**sample**

**IR-be am**

**500<PHONE_NUMBER> Wave number, cm-1**

**IR transmittance, %.**

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 89

**IR-beam**

**o 90o**

**sample**

**o C**

**o C**

Fig. 19. IR transmission spectra of the SiC0.4 layer recorded (a) under normal incidence of IR radiation on the sample and (b) at an angle of 73° to the normal to the sample surface.

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

**500<PHONE_NUMBER> Wave number, cm-1**

Fig. 18. IR transmission spectra of the SiC0.7 layer recorded (a) under normal incidence of IR radiation on the sample and (b) at an angle of 73° to the normal to the sample surface.

б)

  **IR-beam**

β**=73o 90o**

**sample**

**500<PHONE_NUMBER> Wave number, cm-1**

**500<PHONE_NUMBER> Wave number, cm-1**

**IR transmittance, % .**

α**=90o**

a) **sample**

**IR-beam**

**20o C**

Fig. 18. IR transmission spectra of the SiC0.7 layer recorded (a) under normal incidence of IR radiation on the sample and (b) at an angle of 73° to the normal to the sample surface.

**200o C**

**400o C**

**900o C**

**1000o C**

**800o C**

**700o C**

**600o C**

**1200o C**

**1100o C**

**1300o C**

**о C**

Fig. 19. IR transmission spectra of the SiC0.4 layer recorded (a) under normal incidence of IR radiation on the sample and (b) at an angle of 73° to the normal to the sample surface.

The Formation of Silicon Carbide in the SiCx Layers

**o**

**sample**

**IR-be am**

**a)**

**IR transmittance, %.**

> **500<PHONE_NUMBER> Wave number, см**

**-1**

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 91

**б)**

**IR-beam**

**o 90o**

**sample**

**500<PHONE_NUMBER>**

**-1**

**Wave number, см**

**o C**

Fig. 21. IR transmission spectra of the SiC0.03 layer recorded (a) under normal incidence of IR radiation on the sample and (b) at an angle of 73° to the normal to the sample surface.

The position of the minimum of the IR transmission peak determines a certain type of bonds, which corresponds to the maximum of absorption at a given temperature. All layers considered here, exhibit after implantation, a transmission peak with the minimum at a frequency of 720−750 cm–1, which is usually typical of amorphous silicon

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

Fig. 20. IR transmission spectra of the SiC0.12 layer recorded (a) under normal incidence of IR radiation on the sample and (b) at an angle of 73° to the normal to the sample surface.

**IR-beam**

б)

**o 90o**

**sample**

> **500<PHONE_NUMBER> Wave numbe r, cm-1**

**500<PHONE_NUMBER> Wave numbe r, cm-1**

**IR transmittance, %.**

**o**

a) **sample**

**IR -beam**

**o C**

**Tк**

Fig. 20. IR transmission spectra of the SiC0.12 layer recorded (a) under normal incidence of IR radiation on the sample and (b) at an angle of 73° to the normal to the sample surface.

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

**o C**

Fig. 21. IR transmission spectra of the SiC0.03 layer recorded (a) under normal incidence of IR radiation on the sample and (b) at an angle of 73° to the normal to the sample surface.

The position of the minimum of the IR transmission peak determines a certain type of bonds, which corresponds to the maximum of absorption at a given temperature. All layers considered here, exhibit after implantation, a transmission peak with the minimum at a frequency of 720−750 cm–1, which is usually typical of amorphous silicon

The Formation of Silicon Carbide in the SiCx Layers

(Fig. 23, curve 1).

**950**

**710**

SiC0.03.

**730**

**750**

**770**

**3**

**2 4**

**1**

**790**

IR peak wave number, см-1 .

**810**

**830**

**970**

**990**

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 93

As a result of subsequent annealing, the peak is displaced to the right up to 800 cm-1 (Fig. 23), indicating the formation of tetrahedral bonds typical of SiC, increases in amplitude and narrows. In the case of incidence of infrared radiation on the sample surface at the Brewster angle (73° from the normal), after annealing at 1000°C the appearance of the LO-phonon peak of SiC at frequency 955−965 cm-1 is observed for the layers with a high concentration of carbon SiC1.4, SiC0.95 and SiC0.7. With increasing of annealing temperature, this peak increases in amplitude synchronously with the peak of TO-phonons of silicon carbide (Figs. 16−18, 23). For layers with low carbon concentration SiC0.4, SiC0.12 and SiC0.03 the LO-phonon peak of SiC was not observed (Fig. 19−21), which may be associated with small crystallite sizes of silicon carbide. At normal incidence of infrared radiation LO-phonon peak was not observed at both high and low concentrations of carbon (Figs. 16−21). Increase of the annealing temperature in the range 1000−1300°C results in some increase in the wavelength of the amplitude maximum of LO-phonon peak in the case of an excess of carbon for SiC1.4

**0 200 400<PHONE_NUMBER> 1200 1400**

 **TO**

**6**

**0 200 400<PHONE_NUMBER> 1200 1400** Annealing temperature, о

Fig. 23. Wavenumber of the IR transmittance peak for TO- and LO-phonons SiC as a function of the annealing temperature: 1 - SiC1.4, 2 - SiC0.95, 3 - SiC0.7, 4 - SiC0.4, 5 - SiC0.12, 6 -

**5**

С

**LO**

**1**

**3**

**2**

carbide (Figs. 16-22). For the layers with low carbon concentration SiC0.4, SiC0.12 and SiC0.03, the minimum of IR transmission is shifted in the region 720−725 cm-1 to the left relative position of the minimum peak for the layers with a high concentration of carbon SiC1.4, SiC0.95 and SiC0.7, located in the region 735−750 cm-1 (Fig. 23). This may be due to the prevalence of long weak Si−C-bonds in the layers with low carbon concentration.

Fig. 22. IR transmission spectra of the SiC1.4, SiC0.95, SiC0.7, SiC0.4, SiC0.12 and SiC0.03 layers recorded after implantation of C12 ions (E = 40, 20, 10, 5 and 3 kev) into Si (a) and annealing for 30 min at temperatures 600°С (b), 1000°С (c) and 1300°С (d).

carbide (Figs. 16-22). For the layers with low carbon concentration SiC0.4, SiC0.12 and SiC0.03, the minimum of IR transmission is shifted in the region 720−725 cm-1 to the left relative position of the minimum peak for the layers with a high concentration of carbon SiC1.4, SiC0.95 and SiC0.7, located in the region 735−750 cm-1 (Fig. 23). This may be due to the prevalence of long weak Si−C-bonds in the layers with low carbon

**C c)1000o**

**500<PHONE_NUMBER>**

**500<PHONE_NUMBER>**

**500<PHONE_NUMBER> Wave number, cm-1**

for 30 min at temperatures 600°С (b), 1000°С (c) and 1300°С (d).

**500<PHONE_NUMBER> Wave number, cm-1**

SiC1.

SiC0.95

SiC0.7

SiC0.4

SiC0.12

SiC0.03

**C b)600**

**а)20o**

SiC1.4

Fig. 22. IR transmission spectra of the SiC1.4, SiC0.95, SiC0.7, SiC0.4, SiC0.12 and SiC0.03 layers recorded after implantation of C12 ions (E = 40, 20, 10, 5 and 3 kev) into Si (a) and annealing

SiC0.95

SiC0.7

SiC0.4

SiC0.12

SiC0.03

**o**

SiC1.4

SiC0.95

SiC0.7

Т1 Т2

SiC0.4

SiC0.12

SiC0.03

**C d)1300o**

**Wave number, cm-1**  SiC1.4

SiC0.95

SiC0.7

SiC0.4

SiC0.12

**C**

**Wave number, cm-1**

concentration.

**80**

**40**

**80**

**40**

**80**

**40**

**IR transmittance, %.**

**80**

**40**

**80**

**40**

**40**

**80**

As a result of subsequent annealing, the peak is displaced to the right up to 800 cm-1 (Fig. 23), indicating the formation of tetrahedral bonds typical of SiC, increases in amplitude and narrows. In the case of incidence of infrared radiation on the sample surface at the Brewster angle (73° from the normal), after annealing at 1000°C the appearance of the LO-phonon peak of SiC at frequency 955−965 cm-1 is observed for the layers with a high concentration of carbon SiC1.4, SiC0.95 and SiC0.7. With increasing of annealing temperature, this peak increases in amplitude synchronously with the peak of TO-phonons of silicon carbide (Figs. 16−18, 23). For layers with low carbon concentration SiC0.4, SiC0.12 and SiC0.03 the LO-phonon peak of SiC was not observed (Fig. 19−21), which may be associated with small crystallite sizes of silicon carbide. At normal incidence of infrared radiation LO-phonon peak was not observed at both high and low concentrations of carbon (Figs. 16−21). Increase of the annealing temperature in the range 1000−1300°C results in some increase in the wavelength of the amplitude maximum of LO-phonon peak in the case of an excess of carbon for SiC1.4 (Fig. 23, curve 1).

Fig. 23. Wavenumber of the IR transmittance peak for TO- and LO-phonons SiC as a function of the annealing temperature: 1 - SiC1.4, 2 - SiC0.95, 3 - SiC0.7, 4 - SiC0.4, 5 - SiC0.12, 6 - SiC0.03.

The Formation of Silicon Carbide in the SiCx Layers

**g**

**h C C**

**Si**

**f C C C**

**C**

133 173

213

234

**C**

**Si**

**Si**

**Si**

**C**

**Si**

**C C**

**Si**

**Si**

200

194

120

154

160

Fig. 24. Possible variants of both the infrared inactive clusters (a-h), chains of them (b) and a flat net of clusters (a) with various types of bonds between the atoms of Si (great circles) and

It was found that for the layers SiCx with low carbon concentrations (Fig. 23), the minimum of IR transmission peak for the TO-phonons is shifted to above 800 cm-1 as the annealing temperature is increased. In the case of SiC0,4 the position of the peak minimum shifts from 725 to 810 cm-1 in the temperature range 20−1100°C and returns to the 800 cm-1 at 1300°C. In the case of SiC0.12 − from 720 to 820 cm-1 in the range 20−1000°C and returns to 800 cm-1 at 1200°C. In the case of SiC0.03 – from 720 to 830 cm-1 in the range 20−1000°C and does not change its position during 1100−1200°C. Displacement of the peak minimum into the region above 800 cm-1 may be due to the presence of SiC nanocrystals of small size (≤ 3 nm), and an increase in the contribution to the IR absorption amplitude of their surfaces and surfaces of the crystallites Si, containing strong shortened Si−C-bonds. For a layer SiC0.12 and SiC0.4, return of the minimum to 800 cm-1 at temperatures of 1100−1400°C may be caused by incorporation of carbon atoms into the nanocrystals of SiC and the growth of their size up to

The observed shift of the peak minimum indicates the following fact: the absorbing at low frequencies energetically unfavorable long single Si−C-bonds decay during annealing at 600−1000°C, and the stronger short or tetrahedral Si−C-bonds absorbing at higher frequencies, are formed. Since the amplitude of IR transmission at 800 cm–1 is proportional to the concentration of tetrahedral oriented Si−C-bonds, and the amplitude at a certain frequency is assumed to be proportional to the absorption of Si−C-bonds at this frequency, we measured the IR transmittance amplitude for transverse optical (TO) phonons at wavenumbers of 700, 750, 800, 850 and 900 cm–1 after implantation and annealing at 200–

It can be seen from Figs. 25a–c that in the temperature range 20−1300°C, the amplitude of the peak at 800 cm–1 increases from 15 to 62% for the SiC1.4 layer, from 14 to 68% for the SiC0.95 layer, and from 18 to 87% for the SiC0.7 layer. In the interval 20−900°C, the amplitude varies insignificantly. The maximal number of tetrahedral Si−C-bonds at 1300°C is observed in the SiC0.7 layer. For these layers with high carbon concentration, the amplitudes of almost all frequencies (except 900 cm–1) increase at 400°C, which can be due to ordering of the layer

**C**

**e**

3.5-5 nm and higher.

1400°C (Fig. 25).

**Si Si**

**d**

**C Si Si**

**c Si Si**

**Si**

**Si**

**C**

**Si**

**C**

**C**

C (small circles). Bond lengths are presented in pm.

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 95

**b a**

**15**

**1**

**2**

**19**

**18 29**

**17 28**

**27 16**

**3 4 5**

**30 23 8**

**20 21 22**

**24 32 31**

**14 13**

**26**

**25**

**6**

**7**

**9**

**10**

**12 11**

In the case of layers with high concentrations of carbon, position of the minimum of IR transmission peak for TO-phonons is smoothly shifted from 750 to 805 cm-1 for SiC1.4 with the increase of the annealing temperature in the range of 20−1000°C, from 735 to 807 cm-1 for SiC0.95, from 750 to 800 cm-1 for SiC0.7, indicating the formation of tetrahedral oriented Si−Cbonds characteristic of SiC (Fig. 23). The minimum of peak most intensively shifts after annealing in the range 800−900°C, which indicates on intensive processes of the layer ordering. Further annealing up to 1400°C does not lead to a noticeable shift of the minimum peak.

In several studies any changes in the IR transmission spectra have also not revealed after annealing at 1000°C (Borders et al., 1971) and 1100°C (Akimchenko et al., 1977b). This was attributed to the completion of the formation of β-SiC. However, as shown in Fig. 23 for SiC1.4, SiC0.95 and SiC0.7 layers, if the curves of the peak position for TO phonons saturates and does not provide additional information in the temperature range 900−1400°C, then the curves for LO-phonon peak position undergo changes at these temperatures, indicating a structural change in ion-implanted layer. It can be assumed that the formation of tetrahedral Si−C-bonds of required length and angle between them is not completed up to 1300°C.

Although the shift of the minimum of the peak to 800 cm–1 indicating that tetrahedral Si−C-bonds prevail is observed at 1000°C, X-ray diffraction data show that the formation of SiC crystallites begins at 1000°C for SiC0.7, 1150°C for SiC0.95 and 1200°C for SiC1.4 (Figs. 7 and 8), which means that Si−C-bonds are transformed into tetrahedral oriented bonds in the bulk of crystallites only at these temperatures. The increase in the intensity and number of X-ray lines of SiC upon an increase in the annealing temperature (Fig. 8) indicates an increase in the amount of SiC at the expense of the amorphous phase and perfection of its structure due to annealing of structural defects, respectively. It follows that the location of the minimum of transmission peak at ~800 cm-1 and the predominance of the tetrahedral oriented Si-C-bonds among the optically active bonds at temperatures 900−1000°C is not a sufficient condition for the formation of crystallites of silicon carbide in layers with high carbon content SiC0.7 − SiC1.4. At this temperature, a significant part of C and Si atoms can be incorporated in composition of an optically inactive stable clusters, which does not contribute to the amplitude of the IR transmission peak and are decompose at higher temperatures (>1150°C). This results an increase in the amplitude of the infrared transmission at a frequency of 800 cm-1 (Figs. 16, 18 and 22) at these temperatures.

Fig. 24 schematically shows the optically inactive Si−C-clusters, the atoms of which are connected by single, double and triple bonds, lie in one plane. In a flat optically inactive net the free (dangling) bonds to the silicon atoms (atoms №30 and 24) and carbon atoms (№21 and 27) are shown. Free bonds of these and other atoms (№ 4, 11, 12, 15, 17) can connected them with groups of atoms which do not lie on one plane and can form the association of optically active clusters. Since the distance between atoms № 22−4 and №5−22 are equal, the bond can oscillate forming 22−4 and 22−5. One double bond connected three atoms № 5, 6 and 7, i.e. there is the presence of resonance. The presence of two free bonds of the atom № 26 might lead to hybridization, i.e., association. Long single bonds between atoms № 2−3 and 1−18, which decay during low temperature annealing, are shown. Long optically inactive chains, and closed stable clusters of several atoms, connected to each other by double bonds, are also shown in Fig. 24.

In the case of layers with high concentrations of carbon, position of the minimum of IR transmission peak for TO-phonons is smoothly shifted from 750 to 805 cm-1 for SiC1.4 with the increase of the annealing temperature in the range of 20−1000°C, from 735 to 807 cm-1 for SiC0.95, from 750 to 800 cm-1 for SiC0.7, indicating the formation of tetrahedral oriented Si−Cbonds characteristic of SiC (Fig. 23). The minimum of peak most intensively shifts after annealing in the range 800−900°C, which indicates on intensive processes of the layer ordering. Further annealing up to 1400°C does not lead to a noticeable shift of the minimum

In several studies any changes in the IR transmission spectra have also not revealed after annealing at 1000°C (Borders et al., 1971) and 1100°C (Akimchenko et al., 1977b). This was attributed to the completion of the formation of β-SiC. However, as shown in Fig. 23 for SiC1.4, SiC0.95 and SiC0.7 layers, if the curves of the peak position for TO phonons saturates and does not provide additional information in the temperature range 900−1400°C, then the curves for LO-phonon peak position undergo changes at these temperatures, indicating a structural change in ion-implanted layer. It can be assumed that the formation of tetrahedral Si−C-bonds of required length and angle between them is not completed up to 1300°C. Although the shift of the minimum of the peak to 800 cm–1 indicating that tetrahedral Si−C-bonds prevail is observed at 1000°C, X-ray diffraction data show that the formation of SiC crystallites begins at 1000°C for SiC0.7, 1150°C for SiC0.95 and 1200°C for SiC1.4 (Figs. 7 and 8), which means that Si−C-bonds are transformed into tetrahedral oriented bonds in the bulk of crystallites only at these temperatures. The increase in the intensity and number of X-ray lines of SiC upon an increase in the annealing temperature (Fig. 8) indicates an increase in the amount of SiC at the expense of the amorphous phase and perfection of its structure due to annealing of structural defects, respectively. It follows that the location of the minimum of transmission peak at ~800 cm-1 and the predominance of the tetrahedral oriented Si-C-bonds among the optically active bonds at temperatures 900−1000°C is not a sufficient condition for the formation of crystallites of silicon carbide in layers with high carbon content SiC0.7 − SiC1.4. At this temperature, a significant part of C and Si atoms can be incorporated in composition of an optically inactive stable clusters, which does not contribute to the amplitude of the IR transmission peak and are decompose at higher temperatures (>1150°C). This results an increase in the amplitude of the infrared transmission at a frequency of 800 cm-1 (Figs. 16, 18 and 22) at these

Fig. 24 schematically shows the optically inactive Si−C-clusters, the atoms of which are connected by single, double and triple bonds, lie in one plane. In a flat optically inactive net the free (dangling) bonds to the silicon atoms (atoms №30 and 24) and carbon atoms (№21 and 27) are shown. Free bonds of these and other atoms (№ 4, 11, 12, 15, 17) can connected them with groups of atoms which do not lie on one plane and can form the association of optically active clusters. Since the distance between atoms № 22−4 and №5−22 are equal, the bond can oscillate forming 22−4 and 22−5. One double bond connected three atoms № 5, 6 and 7, i.e. there is the presence of resonance. The presence of two free bonds of the atom № 26 might lead to hybridization, i.e., association. Long single bonds between atoms № 2−3 and 1−18, which decay during low temperature annealing, are shown. Long optically inactive chains, and closed stable clusters of several atoms, connected to each other by

peak.

temperatures.

double bonds, are also shown in Fig. 24.

Fig. 24. Possible variants of both the infrared inactive clusters (a-h), chains of them (b) and a flat net of clusters (a) with various types of bonds between the atoms of Si (great circles) and C (small circles). Bond lengths are presented in pm.

It was found that for the layers SiCx with low carbon concentrations (Fig. 23), the minimum of IR transmission peak for the TO-phonons is shifted to above 800 cm-1 as the annealing temperature is increased. In the case of SiC0,4 the position of the peak minimum shifts from 725 to 810 cm-1 in the temperature range 20−1100°C and returns to the 800 cm-1 at 1300°C. In the case of SiC0.12 − from 720 to 820 cm-1 in the range 20−1000°C and returns to 800 cm-1 at 1200°C. In the case of SiC0.03 – from 720 to 830 cm-1 in the range 20−1000°C and does not change its position during 1100−1200°C. Displacement of the peak minimum into the region above 800 cm-1 may be due to the presence of SiC nanocrystals of small size (≤ 3 nm), and an increase in the contribution to the IR absorption amplitude of their surfaces and surfaces of the crystallites Si, containing strong shortened Si−C-bonds. For a layer SiC0.12 and SiC0.4, return of the minimum to 800 cm-1 at temperatures of 1100−1400°C may be caused by incorporation of carbon atoms into the nanocrystals of SiC and the growth of their size up to 3.5-5 nm and higher.

The observed shift of the peak minimum indicates the following fact: the absorbing at low frequencies energetically unfavorable long single Si−C-bonds decay during annealing at 600−1000°C, and the stronger short or tetrahedral Si−C-bonds absorbing at higher frequencies, are formed. Since the amplitude of IR transmission at 800 cm–1 is proportional to the concentration of tetrahedral oriented Si−C-bonds, and the amplitude at a certain frequency is assumed to be proportional to the absorption of Si−C-bonds at this frequency, we measured the IR transmittance amplitude for transverse optical (TO) phonons at wavenumbers of 700, 750, 800, 850 and 900 cm–1 after implantation and annealing at 200– 1400°C (Fig. 25).

It can be seen from Figs. 25a–c that in the temperature range 20−1300°C, the amplitude of the peak at 800 cm–1 increases from 15 to 62% for the SiC1.4 layer, from 14 to 68% for the SiC0.95 layer, and from 18 to 87% for the SiC0.7 layer. In the interval 20−900°C, the amplitude varies insignificantly. The maximal number of tetrahedral Si−C-bonds at 1300°C is observed in the SiC0.7 layer. For these layers with high carbon concentration, the amplitudes of almost all frequencies (except 900 cm–1) increase at 400°C, which can be due to ordering of the layer

The Formation of Silicon Carbide in the SiCx Layers

SiC1.4, SiC0.95, SiC0.7. SiC0.12 and SiC0.03.

approximation:

layers.

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 97

high carbon concentration are almost analogous, but differ considerably from the dependences for SiC0.4, SiC0.12 and SiC0.03 layers with a low carbon concentration. This indicates the same nature of carbon and carbon–silicon clusters in SiC1.4, SiC0.95 and SiC0.7

For SiC0.4, SiC0.12 and SiC0.03 layers with a low carbon concentration, measurements of the IR transmission amplitude show **(**Figure 25, d-f) that in the temperature range 20–1300°C, the amplitude at 800 cm–1 increases from 13 to 52% for the SiC0.4 layer, from 11 to 37% for the SiC0.12 layer, and from 2.8 to 8% for the SiC0.03 layer. At temperatures 20–600°C, in these layers dominate the long and weak Si−C-bonds, which absorb at frequencies of 700 and 750 cm–1 (Fig. 25d-f, curves 1 and 2) and decay at low temperatures. A noticeable increase in the amplitudes is observed at frequencies of 800 and 850 cm–1 in the temperature range 700−1000°C, which indicates an increase in the number of tetrahedral and nearly to tetrahedral short Si−C-bonds. A distinguishing feature for SiC0.4, SiC0.12 and SiC0.03 layers with a low carbon concentration is an intense increase in the number of tetrahedral bonds at low temperatures (700°C), which is due to a low concentration of stable carbon clusters (chains, flat nets, etc.) disintegrating at higher temperatures, because low content of carbon atoms. Consequently, in the range of 800−900ºC by the number of tetrahedral Si−C-bonds and the amplitude at 800 cm-1 (35%) the SiC0.4 layers exceed all the above considered layers

For SiC0.4 and SiC0.12 layers in the temperature range 700−1100°C, the increase in the amplitudes at frequencies of 800, 850, and 900 cm–1 is accompanied by a decrease in the amplitudes at 700 and 750 cm–1, indicating an increase in the number of tetrahedral and strong short Si−C-bonds due to disintegration of long weak bonds that prevailed after implantation. Intensive formation of Si−C-bonds with the tetrahedral orientation, which absorb at a frequency of 800 cm–1 (Fig 25d and e, curves 3) at 1200°C is due to disintegration of strong optically inactive clusters of C and Si atoms. The SiC0.4 layer with a higher carbon concentration differs from the SiC0.12 layer because it contains stronger clusters disintegrating at 1300°C, which is manifested in a sharp increase in the amplitude at this temperature. As in the case of SiC1.4, SiC0.95 and SiC0.7 layers with a high carbon concentration, the decrease in the amplitudes for SiC0.4 at 1400°C is due to disintegration of

Increase in the number of tetrahedral bonds in the layer SiC0.03 in the temperature range 800−900°C occurs simultaneously with some increase in amplitude for all frequencies, i.e. not due to the decay of optically active bonds. For this layer with very low carbon concentration is difficult to assume the presence of a noticeable amount of stable carbon and carbon-silicon clusters. We can assume that a significant increase of tetrahedral bonds can

We assume that the total area of the SiC-peak of IR transmission is the area of region between the curve of the IR spectrum and the baseline |Т1Т2| (Fig. 16a), and it is equal to the total absorption of infrared radiation at all frequencies and is roughly proportional to the number of all types of absorbing Si−C-bonds (Wong et al., 1998; Chen et al., 1999). Peak area was determined from the spectra of IR transmission (Figs. 16−21), based on the

1 22 1 1 22 1

 τν ν

*A TT* = + −− ( )( ) ( ) ( )( ) ( )

*d TT* ≈ + −−

ν ν  τ ν δν

, (2)

SiC crystallites and desorption of carbon from the layer (Fig. 25d, curves 2–5).

occur by reducing the number of dangling bonds of carbon atoms.

1 1 2 2

ν ν

and the formation of optically active Si−C-bonds. A certain increase in the amplitude at 800 cm–1 indicates the formation of tetrahedral Si−C-bonds at low temperatures.

Fig. 25. Effect of the annealing temperature on the IR transmittance amplitude at wavenumbers of (1-□) 700 cm-1, (2-∆) 750 cm-1, (3-○) 800 cm-1, (4-▲) 850 cm-1, and (5-■) 900 cm-1 under normal incidence of IR radiation on the sample surface: a) SiC1.4; b) SiC0.95; c) SiC0.7, d) SiC0.4, e) SiC0.12; f) SiC0.03.

The amplitudes at 800 cm–1 and close frequencies of 750 and 850 cm–1 considerably increase after annealing at temperatures in the interval 900−1300°C. This means that in SiC1.4, SiC0.95 and SiC0.7 layers with a high carbon concentration, intense formation of tetrahedral Si–C bonds begins at 900−1000°C and continues up to 1300°C. This can be due to breakdown of carbon and silicon clusters (chains and flat nets) as well as single Si−C-bonds during annealing. The most pronounced decay of long single Si−C-bonds absorbing at a frequency of 700 cm–1 **(**Fig. 25a**-c**, curve 1) occurs during annealing at 800−1200°C. Annealing of SiC1.4, SiC0.95 and SiC0.7 layers at 1400°C resulted in a decrease in the amplitudes in the entire frequency range 700−900 cm–1, which is apparently due to decomposition of SiC as a result of carbon desorption from the layer. It can be seen from Fig. 25 that the dependences of IR transmission amplitudes on the annealing temperature for different wavenumbers for SiC1.4, SiC0.95 and SiC0.7 layers with a

and the formation of optically active Si−C-bonds. A certain increase in the amplitude at 800

**b)SiC0.95**

**3**

**0<PHONE_NUMBER> Температура,**

**e)SiC0.12**

**0<PHONE_NUMBER> Тemperature, о**

**1**

**5 1**

**о С**

**3 4**

**5**

**2**

**С**

**4**

**2**

**0<PHONE_NUMBER> Температура,**

**f)SiC0.03**

**3**

**1**

**0<PHONE_NUMBER> Тemperature, о**

**c)SiC0.7**

**о С**

**4**

**С**

**2**

**5**

**2**

**1 5**

**3 4**

cm–1 indicates the formation of tetrahedral Si−C-bonds at low temperatures.

**Amplitude,**

**%**

**5**

**Amplitude, %.**

**0<PHONE_NUMBER> Температура,**

**d)SiC0.4**

**0<PHONE_NUMBER> Тemperature, о**

c) SiC0.7, d) SiC0.4, e) SiC0.12; f) SiC0.03.

**5 1**

**а)SiC1.4**

**3**

**1**

**о С**

**3 4**

**2**

**С**

Fig. 25. Effect of the annealing temperature on the IR transmittance amplitude at

wavenumbers of (1-□) 700 cm-1, (2-∆) 750 cm-1, (3-○) 800 cm-1, (4-▲) 850 cm-1, and (5-■) 900 cm-1 under normal incidence of IR radiation on the sample surface: a) SiC1.4; b) SiC0.95;

The amplitudes at 800 cm–1 and close frequencies of 750 and 850 cm–1 considerably increase after annealing at temperatures in the interval 900−1300°C. This means that in SiC1.4, SiC0.95 and SiC0.7 layers with a high carbon concentration, intense formation of tetrahedral Si–C bonds begins at 900−1000°C and continues up to 1300°C. This can be due to breakdown of carbon and silicon clusters (chains and flat nets) as well as single Si−C-bonds during annealing. The most pronounced decay of long single Si−C-bonds absorbing at a frequency of 700 cm–1 **(**Fig. 25a**-c**, curve 1) occurs during annealing at 800−1200°C. Annealing of SiC1.4, SiC0.95 and SiC0.7 layers at 1400°C resulted in a decrease in the amplitudes in the entire frequency range 700−900 cm–1, which is apparently due to decomposition of SiC as a result of carbon desorption from the layer. It can be seen from Fig. 25 that the dependences of IR transmission amplitudes on the annealing temperature for different wavenumbers for SiC1.4, SiC0.95 and SiC0.7 layers with a

**4**

**2**

high carbon concentration are almost analogous, but differ considerably from the dependences for SiC0.4, SiC0.12 and SiC0.03 layers with a low carbon concentration. This indicates the same nature of carbon and carbon–silicon clusters in SiC1.4, SiC0.95 and SiC0.7 layers.

For SiC0.4, SiC0.12 and SiC0.03 layers with a low carbon concentration, measurements of the IR transmission amplitude show **(**Figure 25, d-f) that in the temperature range 20–1300°C, the amplitude at 800 cm–1 increases from 13 to 52% for the SiC0.4 layer, from 11 to 37% for the SiC0.12 layer, and from 2.8 to 8% for the SiC0.03 layer. At temperatures 20–600°C, in these layers dominate the long and weak Si−C-bonds, which absorb at frequencies of 700 and 750 cm–1 (Fig. 25d-f, curves 1 and 2) and decay at low temperatures. A noticeable increase in the amplitudes is observed at frequencies of 800 and 850 cm–1 in the temperature range 700−1000°C, which indicates an increase in the number of tetrahedral and nearly to tetrahedral short Si−C-bonds. A distinguishing feature for SiC0.4, SiC0.12 and SiC0.03 layers with a low carbon concentration is an intense increase in the number of tetrahedral bonds at low temperatures (700°C), which is due to a low concentration of stable carbon clusters (chains, flat nets, etc.) disintegrating at higher temperatures, because low content of carbon atoms. Consequently, in the range of 800−900ºC by the number of tetrahedral Si−C-bonds and the amplitude at 800 cm-1 (35%) the SiC0.4 layers exceed all the above considered layers SiC1.4, SiC0.95, SiC0.7. SiC0.12 and SiC0.03.

For SiC0.4 and SiC0.12 layers in the temperature range 700−1100°C, the increase in the amplitudes at frequencies of 800, 850, and 900 cm–1 is accompanied by a decrease in the amplitudes at 700 and 750 cm–1, indicating an increase in the number of tetrahedral and strong short Si−C-bonds due to disintegration of long weak bonds that prevailed after implantation. Intensive formation of Si−C-bonds with the tetrahedral orientation, which absorb at a frequency of 800 cm–1 (Fig 25d and e, curves 3) at 1200°C is due to disintegration of strong optically inactive clusters of C and Si atoms. The SiC0.4 layer with a higher carbon concentration differs from the SiC0.12 layer because it contains stronger clusters disintegrating at 1300°C, which is manifested in a sharp increase in the amplitude at this temperature. As in the case of SiC1.4, SiC0.95 and SiC0.7 layers with a high carbon concentration, the decrease in the amplitudes for SiC0.4 at 1400°C is due to disintegration of SiC crystallites and desorption of carbon from the layer (Fig. 25d, curves 2–5).

Increase in the number of tetrahedral bonds in the layer SiC0.03 in the temperature range 800−900°C occurs simultaneously with some increase in amplitude for all frequencies, i.e. not due to the decay of optically active bonds. For this layer with very low carbon concentration is difficult to assume the presence of a noticeable amount of stable carbon and carbon-silicon clusters. We can assume that a significant increase of tetrahedral bonds can occur by reducing the number of dangling bonds of carbon atoms.

We assume that the total area of the SiC-peak of IR transmission is the area of region between the curve of the IR spectrum and the baseline |Т1Т2| (Fig. 16a), and it is equal to the total absorption of infrared radiation at all frequencies and is roughly proportional to the number of all types of absorbing Si−C-bonds (Wong et al., 1998; Chen et al., 1999). Peak area was determined from the spectra of IR transmission (Figs. 16−21), based on the approximation:

$$A = \frac{1}{2}(T\_1 + T\_2)(\nu\_2 - \nu\_1) - \frac{1}{2}\pi(\nu)d\nu = \frac{1}{2}(T\_1 + T\_2)(\nu\_2 - \nu\_1) - \Sigma\,\pi(\nu)\delta\nu\,\,\tag{2}$$

The Formation of Silicon Carbide in the SiCx Layers

carbon concentration, basing on data of the peak area (Table 4).

spectra for SiCх layers after implantation and annealing

T, ºС A, arb. un.

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 99

partial decay of the clusters at 1300°C, the estimations of the proportion of carbon atoms included in the optically inactive clusters suggest even higher values. In general, the assertions do not contradict the data (Chen et al., 2003; Wong et al., 1998; Chen et al., 1999), where the growths of area of Si−C-peak after annealing, were shown. We evaluated the linearity of the dependence of the area and number of optically active Si−C-bonds on the

SiC0.03 SiC0.12 SiC0.4 SiC0.7 SiC0.95 SiC1.4

20ºС 1709 3588 4719 6622 3848 4384 200ºС 1840 3990 4929 6966 4198 5347 400ºС 1464 3921 4638 7647 4571 5757 600ºС 1672 3979 4595 8296 5152 5442 700ºС 1963 4248 5035 8227 5394 5665 800ºС 1127 3795 6061 7428 5458 5864 900ºС 1924 4004 5150 7772 5571 6619 1000ºС 2708 3958 4499 7674 5386 7664 1100ºС 2069 3910 4437 8158 6296 7190 1200ºС 2428 5181 5428 7980 7570 8011 1300ºС 0 4886 5805 10169 10221 10953 1400ºС 5473 4749 5510 7741 8670 Table 4. Area, A, under the IR transmittance SiC-peak for TO phonons obtained from the IR

In the layer SiC0.03 the number of optically active Si−C-bonds after annealing should be roughly proportional to the quantity of carbon atoms due to the low concentration of carbon and stable carbon or carbon-silicon clusters as well. We take the maximum value of the area of Si−C-peak for the SiC0.03 layer at 1000ºC as equal to 1. If the proportionality is linear, an increase in the concentration of carbon in SiCх layer on n1 times (n1= (NC/NSi)/0.03 = х/0.03) should increase the peak area on n2 times (n2 = Aх(T)/A0.03(1000ºС)), and n1 = n2, if not come saturation in the amplitude of the transmission, and the carbon atoms are not included in the optically inactive clusters. Since the saturation amplitude of the IR transmission is not reached (Fig. 25) and n2 < n1, so a values 100%×n2/n1 show the portion of carbon atoms forming optically active Si−Cbonds in the SiCx layer. As it turned out, at 1300ºC in the layer SiC1.4 only 9% of the C atoms form the optically active Si−C-bonds, in SiC0.95 − 12%, in SiC0.7 and SiC0.4 − 16%, in SiC0.12 − 45%, while the other carbon atoms remain in the composition of strong clusters. The total number of SiC (optically active Si−C-bonds) in the SiCх layers after annealing at 1300ºC increases with the

fractional degree of carbon concentration (х/0.03)y, where *y* ~ 0.37±0.09 (Table 5).

one of which belonged to the amorphous SiC, while the other two to β-SiC.

In (Wong et al., 1998) at a fixed energy the total number of formed SiC increases with the fractional degree of doses, namely, Dy witg «y» defined as 0.41. In this paper, SiC layers were synthesized using the ion source MEVVA implantation in p-Si of carbon ions with energies in the range 30−60 keV and doses ranged within (0.3–1.6)×1018 см-2. In this case, the infrared absorption spectra of SiC layers were decomposed into two or three components,

where A − total absorption (or transmission) in relative units in the frequency range ν1<ν<ν2, τ(ν) − transmission at frequency ν, Т1 and Т2 − the values of IR transmission at frequencies ν1 and ν2, respectively, δν − step of measurements, equal to 2.5 or 5 cm-1. Fig. 26 shows the peak area of IR transmission for TO phonons as a function of the annealing temperature and the concentration of carbon for layers SiC1.4, SiC0.95, SiC0.7, SiC0.4, SiC0.12 and SiC0.03. It is seen that in the range of 27−1200°C the number of optically active Si−C-bonds is highest in the layer SiC0.7. A smaller number of Si−C-bonds in the SiCх layers if x<0.7 is caused by lower carbon content, and if x>0.7 − due to the high concentration of stable clusters, decomposing at higher temperatures. Therefore, at 1300°C number of optical active Si−C-bonds is the highest in layer SiC1.4.

Fig. 26. Effect of the annealing temperature and concentration of carbon on the area under the IR transmittance SiC-peak for TO phonons under normal incidence of IR radiation on the sample surface: a) SiC1.4 (1), SiC0.95 (2), SiC0.7 (3), SiC0.4 (4), SiC0.12 (5) и SiC0.03 (6); b) 27 ºC (1), 400°C (2), 800°C (3), 1000°C (4), 1200°C (5), 1300°C (6), 1400°C (7).

For layers SiC1.4, SiC0.95 and SiC0.7 with high carbon concentration, the peak area of IR transmission immediately after implantation has the lowest value (Fig. 26a). In the temperature range 20−1400°C, the value of the peak area for SiC1.4 is changed in the range of values within 4380−10950 arb. units, for SiC0.95 − within 3850−10220 units, for SiC0.7 − within 6620−10170 units, and tends to increase with annealing temperature, indicating a significant amount of carbon atoms do not bound with silicon in the layers immediately after implantation: ∼[1−(4380/10950)×100/1.4] ≈ 70% for SiC1.4, ∼[1− (3850/10220)]×100% ≈ 62% for SiC0.95, ∼[1–(6620/10170)]×100% ≈ 35% for SiC0.7. These estimates can be valid if we assuming that after annealing at 1300°C all clusters broke up and all carbon atoms formed optically active Si−C-bonds in the layer (except the excess atoms in SiC1.4). In the case of a

where A − total absorption (or transmission) in relative units in the frequency range ν1<ν<ν2, τ(ν) − transmission at frequency ν, Т1 and Т2 − the values of IR transmission at

Fig. 26 shows the peak area of IR transmission for TO phonons as a function of the annealing temperature and the concentration of carbon for layers SiC1.4, SiC0.95, SiC0.7, SiC0.4, SiC0.12 and SiC0.03. It is seen that in the range of 27−1200°C the number of optically active Si−C-bonds is highest in the layer SiC0.7. A smaller number of Si−C-bonds in the SiCх layers if x<0.7 is caused by lower carbon content, and if x>0.7 − due to the high concentration of stable clusters, decomposing at higher temperatures. Therefore, at 1300°C number of optical

**4**

**0**

**0 0,3 0,6 0,9 1,2 Nc/Nsi**

**1**

**4**

**5**

**2**

**3**

**7**

**2000**

**4000**

**6000**

**8000**

**10000**

**6**

**b)**

**12000**

**2**

**1 а) b)**

frequencies ν1 and ν2, respectively, δν − step of measurements, equal to 2.5 or 5 cm-1.

active Si−C-bonds is the highest in layer SiC1.4.

**3**

**0**

**0 300<PHONE_NUMBER> Temperature, о**

(1), 400°C (2), 800°C (3), 1000°C (4), 1200°C (5), 1300°C (6), 1400°C (7).

**5**

**С**

Fig. 26. Effect of the annealing temperature and concentration of carbon on the area under the IR transmittance SiC-peak for TO phonons under normal incidence of IR radiation on the sample surface: a) SiC1.4 (1), SiC0.95 (2), SiC0.7 (3), SiC0.4 (4), SiC0.12 (5) и SiC0.03 (6); b) 27 ºC

For layers SiC1.4, SiC0.95 and SiC0.7 with high carbon concentration, the peak area of IR transmission immediately after implantation has the lowest value (Fig. 26a). In the temperature range 20−1400°C, the value of the peak area for SiC1.4 is changed in the range of values within 4380−10950 arb. units, for SiC0.95 − within 3850−10220 units, for SiC0.7 − within 6620−10170 units, and tends to increase with annealing temperature, indicating a significant amount of carbon atoms do not bound with silicon in the layers immediately after implantation: ∼[1−(4380/10950)×100/1.4] ≈ 70% for SiC1.4, ∼[1− (3850/10220)]×100% ≈ 62% for SiC0.95, ∼[1–(6620/10170)]×100% ≈ 35% for SiC0.7. These estimates can be valid if we assuming that after annealing at 1300°C all clusters broke up and all carbon atoms formed optically active Si−C-bonds in the layer (except the excess atoms in SiC1.4). In the case of a

**2000**

**4000**

**6**

**6000**

**Area under the SiC-peak, arb.un.**

**8000**

**10000**

**12000**

partial decay of the clusters at 1300°C, the estimations of the proportion of carbon atoms included in the optically inactive clusters suggest even higher values. In general, the assertions do not contradict the data (Chen et al., 2003; Wong et al., 1998; Chen et al., 1999), where the growths of area of Si−C-peak after annealing, were shown. We evaluated the linearity of the dependence of the area and number of optically active Si−C-bonds on the carbon concentration, basing on data of the peak area (Table 4).

Table 4. Area, A, under the IR transmittance SiC-peak for TO phonons obtained from the IR spectra for SiCх layers after implantation and annealing

In the layer SiC0.03 the number of optically active Si−C-bonds after annealing should be roughly proportional to the quantity of carbon atoms due to the low concentration of carbon and stable carbon or carbon-silicon clusters as well. We take the maximum value of the area of Si−C-peak for the SiC0.03 layer at 1000ºC as equal to 1. If the proportionality is linear, an increase in the concentration of carbon in SiCх layer on n1 times (n1= (NC/NSi)/0.03 = х/0.03) should increase the peak area on n2 times (n2 = Aх(T)/A0.03(1000ºС)), and n1 = n2, if not come saturation in the amplitude of the transmission, and the carbon atoms are not included in the optically inactive clusters. Since the saturation amplitude of the IR transmission is not reached (Fig. 25) and n2 < n1, so a values 100%×n2/n1 show the portion of carbon atoms forming optically active Si−Cbonds in the SiCx layer. As it turned out, at 1300ºC in the layer SiC1.4 only 9% of the C atoms form the optically active Si−C-bonds, in SiC0.95 − 12%, in SiC0.7 and SiC0.4 − 16%, in SiC0.12 − 45%, while the other carbon atoms remain in the composition of strong clusters. The total number of SiC (optically active Si−C-bonds) in the SiCх layers after annealing at 1300ºC increases with the fractional degree of carbon concentration (х/0.03)y, where *y* ~ 0.37±0.09 (Table 5).

In (Wong et al., 1998) at a fixed energy the total number of formed SiC increases with the fractional degree of doses, namely, Dy witg «y» defined as 0.41. In this paper, SiC layers were synthesized using the ion source MEVVA implantation in p-Si of carbon ions with energies in the range 30−60 keV and doses ranged within (0.3–1.6)×1018 см-2. In this case, the infrared absorption spectra of SiC layers were decomposed into two or three components, one of which belonged to the amorphous SiC, while the other two to β-SiC.

The Formation of Silicon Carbide in the SiCx Layers

and annealing at higher temperature removes the differences.

graphite grains, beginning from W = 0.5 J/cm2.

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 101

Evaluation results may be debatable, since the literature contains different points of view concerning inclusion of carbon into SiC. Akimchenko et al. (1977a) after implantation of Si (Е = 40 кэВ, D = 3.7×1017 см-2) in diamond and annealing at temperatures of 500-1200ºC assumed that almost 100% of implanted carbon atoms included in the SiC. This conclusion was made from accordance of calculated layer thickness (80 nm) with ones found from the absorption near 810 cm-1 (70 nm). A comparison with the magnitude of the SiC thickness (8−10 nm) obtained by X-ray diffraction, allowed to conclude that 10−15% of atoms of the disordered SiC united into β-SiC crystallites, which contribute to the X-ray reflection, and the rest remains in the amorphous state. Kimura et al. (1982) basing on data from the optical density of the infrared transmission spectra have established that all implanted carbon are included in β-SiC after annealing at 900−1200ºC, if the concentration of implanted carbon is less or equal to the stoichiometric composition of SiC at the peak of the distribution. In the case of higher doses, the excess carbon atoms form clusters and are not included into β-SiC, even after annealing at 1200°C. The activation energy required for inclusion of carbon atoms in the β-SiC, increases with increasing of implantation doses, since more energy is required for the decomposition of carbon clusters. Durupt et al. (1980) showed that if the annealing temperature below 900ºC, the formation of SiC is less pronounced in the case of high dose,

On the other hand, Borders et al. (1971) from the infrared absorption and Rutherford backscattering data found that about half of carbon atoms implanted into the silicon (Е = 200 кэВ, D = ~1017 см-2) included in micro-SiC. According to our estimates, the concentration of carbon atoms in the layer was lower than 10% (x <0.1). Kimura et al. (1981) from the analysis of infrared spectra revealed that after implantation (E = 100 keV) and annealing at 900ºC about 40-50% of carbon atoms united with Si atoms to form β-SiC, and this value monotonically increased to 70-80% with increasing of annealing temperature up to 1200ºC. The number of carbon atoms included in the β-SiC was affected by dose of carbon ions. Calcagno et al. (1996) showed that the optical band gap and the intensity of the infrared signal after annealing at 1000ºC increased linearly with carbon concentration, reaching a maximum at the stoichiometric composition of SiC. At higher carbon concentrations intensity of the infrared signal undergoes saturation, and the band gap decreases from 2.2 to 1.8 eV. By Raman spectroscopy is shown that this is due to the formation of clusters of graphite. Simon et al. (1996) after the high-temperature (700ºC) implantation of carbon ions into Si (E = 50 keV, D = 1018 and 2×1018 см-2) show that the carbon excess precipitates out, forming carbon clusters. It is assumed that the stresses and defects, formed after the first stage of implantation, form traps, which attract the following carbon atoms. Liangdeng et al. (2008) after implantation of C ions (E = 80 keV, D = 2.7×1017 ион/cм2) in the Raman spectra observed double band with center in 1380 and 1590 cm-1 corresponding to the range of graphitized amorphous carbon. The authors suggest that since solid solubility of carbon in a-Si at a temperature close to the melting point of Si, is about 1017/cm3, and almost disappears at room temperature, the carbon has a tendency to form precipitates. Bayazitov et al. (2003) after implantation of carbon ions (E = 40 keV, D = 5*×*1017 см*−*2) in silicon and pulsed ion beam annealing (*W* = 1.0 J/cm2, C+(~80%) and H+(~20%)) have formed a β-SiC layer with an average size of grain about 100 nm. Increasing the energy density per pulse up to 1.5 J/cm2 leads also to appearance of graphite grains of sizes about 100 nm, as well as visually observed darkening of the sample. When exposed by radiation of ruby laser (λ = 0.69 μm, τ = 50 nsec, W = 0.5-2 J/cm2) also formed the

Really, as seen in Table 5, the increase of carbon concentration x in the layer SiC0,12 in 4 times in comparison with SiC0.03 results to a smaller increase in the area of SiC-peak, pointing to the disproportionate increase in the number of optically active Si−C-bonds . At least, the maximum area at 1200ºC for a SiC0.12 layer exceeds the maximum area for SiC0,03 layer only in 1.91 times. Further increase in the concentration of carbon x in the SiCх layers in 13, 23, 32, 47 times leads to an increase in the number of optically active Si−C-bonds in several times less than expected − no more than 4.04 times even for high temperature annealing.

Both the peak areas and the number of bonds do not increase linearly with the increase of concentration and it is not caused by saturation of amplitude values. As in the case of NC/NSi = 0.12, the increase of concentration in 13.3 times at NC/NSi = 0.4, has led to an increase in the amplitude of only 9 times, and an area of 2.1 times (5805 un.) at 1300ºC (Tables 4 and 5), although the amplitude of the IR transmittance at the minimum of the peak is far from saturation (52%). This confirms that the determining factor is the presence of strong clusters, in the structure of which is included the majority of the carbon atoms. That is at 1300ºC in the SiC0.4 layer only n1/n2 = 2.1/13.33 = 16% of the carbon atoms form an optically active Si−C-bonds, and in the SiC0.12 layer − 45%. Then, in the optically inactive stable clusters are included the rest 84% and 55% of carbon atoms (Table 5), respectively, resulting in no increase in peak area proportionally to the concentration of carbon. Since there is a predominance of the tetrahedral oriented bonds among the optically active Si-Cbonds, the amount of tetrahedral Si−C-bonds is sufficient for the appearance of SiC crystallites in the layers, which is observed on the X-ray diffraction pattern.

Table 5. Relative values of area (n2 = Ax(T)/A0.03(1000°C)) of IR transmission SiC-peak and the proportion of carbon atoms (100% × n2/n1) which forms an optically active Si-C-bonds in the SiCx layers.

Really, as seen in Table 5, the increase of carbon concentration x in the layer SiC0,12 in 4 times in comparison with SiC0.03 results to a smaller increase in the area of SiC-peak, pointing to the disproportionate increase in the number of optically active Si−C-bonds . At least, the maximum area at 1200ºC for a SiC0.12 layer exceeds the maximum area for SiC0,03 layer only in 1.91 times. Further increase in the concentration of carbon x in the SiCх layers in 13, 23, 32, 47 times leads to an increase in the number of optically active Si−C-bonds in several times

Both the peak areas and the number of bonds do not increase linearly with the increase of concentration and it is not caused by saturation of amplitude values. As in the case of NC/NSi = 0.12, the increase of concentration in 13.3 times at NC/NSi = 0.4, has led to an increase in the amplitude of only 9 times, and an area of 2.1 times (5805 un.) at 1300ºC (Tables 4 and 5), although the amplitude of the IR transmittance at the minimum of the peak is far from saturation (52%). This confirms that the determining factor is the presence of strong clusters, in the structure of which is included the majority of the carbon atoms. That is at 1300ºC in the SiC0.4 layer only n1/n2 = 2.1/13.33 = 16% of the carbon atoms form an optically active Si−C-bonds, and in the SiC0.12 layer − 45%. Then, in the optically inactive stable clusters are included the rest 84% and 55% of carbon atoms (Table 5), respectively, resulting in no increase in peak area proportionally to the concentration of carbon. Since there is a predominance of the tetrahedral oriented bonds among the optically active Si-Cbonds, the amount of tetrahedral Si−C-bonds is sufficient for the appearance of SiC

SiCx SiC 0.03 SiC 0.12 SiC 0.4 SiC 0.7 SiC 0.95 SiC 1.4.

T, ºС A0.03 % A0.03 % A0.03 % A0.03 % A0.03 % A0.03 % 20 0.63 63 1.3. 33 1.7. 13 2.4. 10 1.4. 4 1.6. 3 200 0.68. 68 1.5. 37 1.8 14 2.6 11 1.6 5 2.0 4 400 0.54 54 1,4 36 1.7 13 2.8 12 1.7 5 2.1 5 600 0.62 62 1.5 37 1.7 13 3.1 13 1.9 6 2.0 4 700 0.72 72 1.6 39 1.9 14 3.0 13 2.0 6 2.1 4 800 0.42 42 1.4 35 2.2 17 2.7 12 2.0 6 2.2 5 900 0.71 71 1.5 37 1.9 14 2.9 12 2.1 6 2.4 5 1000 1.00 100 1.5 37 1.7 12 2.8 12 2.0 6 2.8 6 1100 0.76 76 1.4 36 1.6 12 3.0 13 2.3 7 2.7 6 1200 0.90 90 1.9 48 2.0 15 2.9 13 2.8 9 3.0 6 1300 90 1.8 45 2.1 16 3.8 16 3.8 12 4.0 9

Ax Si-C Ax Si-C Ax Si-C Ax Si-C Ax Si-C Ax Si-C

n1=х/0.03 1.0 4.0 13.3. 23.3. 31.7. 46.7.

y(1300ºС) 0.40 0.28 0.42 0.38 0.36

the SiCx layers.

Table 5. Relative values of area (n2 = Ax(T)/A0.03(1000°C)) of IR transmission SiC-peak and the proportion of carbon atoms (100% × n2/n1) which forms an optically active Si-C-bonds in

less than expected − no more than 4.04 times even for high temperature annealing.

crystallites in the layers, which is observed on the X-ray diffraction pattern.

Evaluation results may be debatable, since the literature contains different points of view concerning inclusion of carbon into SiC. Akimchenko et al. (1977a) after implantation of Si (Е = 40 кэВ, D = 3.7×1017 см-2) in diamond and annealing at temperatures of 500-1200ºC assumed that almost 100% of implanted carbon atoms included in the SiC. This conclusion was made from accordance of calculated layer thickness (80 nm) with ones found from the absorption near 810 cm-1 (70 nm). A comparison with the magnitude of the SiC thickness (8−10 nm) obtained by X-ray diffraction, allowed to conclude that 10−15% of atoms of the disordered SiC united into β-SiC crystallites, which contribute to the X-ray reflection, and the rest remains in the amorphous state. Kimura et al. (1982) basing on data from the optical density of the infrared transmission spectra have established that all implanted carbon are included in β-SiC after annealing at 900−1200ºC, if the concentration of implanted carbon is less or equal to the stoichiometric composition of SiC at the peak of the distribution. In the case of higher doses, the excess carbon atoms form clusters and are not included into β-SiC, even after annealing at 1200°C. The activation energy required for inclusion of carbon atoms

in the β-SiC, increases with increasing of implantation doses, since more energy is required for the decomposition of carbon clusters. Durupt et al. (1980) showed that if the annealing temperature below 900ºC, the formation of SiC is less pronounced in the case of high dose, and annealing at higher temperature removes the differences.

On the other hand, Borders et al. (1971) from the infrared absorption and Rutherford backscattering data found that about half of carbon atoms implanted into the silicon (Е = 200 кэВ, D = ~1017 см-2) included in micro-SiC. According to our estimates, the concentration of carbon atoms in the layer was lower than 10% (x <0.1). Kimura et al. (1981) from the analysis of infrared spectra revealed that after implantation (E = 100 keV) and annealing at 900ºC about 40-50% of carbon atoms united with Si atoms to form β-SiC, and this value monotonically increased to 70-80% with increasing of annealing temperature up to 1200ºC. The number of carbon atoms included in the β-SiC was affected by dose of carbon ions. Calcagno et al. (1996) showed that the optical band gap and the intensity of the infrared signal after annealing at 1000ºC increased linearly with carbon concentration, reaching a maximum at the stoichiometric composition of SiC. At higher carbon concentrations intensity of the infrared signal undergoes saturation, and the band gap decreases from 2.2 to 1.8 eV. By Raman spectroscopy is shown that this is due to the formation of clusters of graphite. Simon et al. (1996) after the high-temperature (700ºC) implantation of carbon ions into Si (E = 50 keV, D = 1018 and 2×1018 см-2) show that the carbon excess precipitates out, forming carbon clusters. It is assumed that the stresses and defects, formed after the first stage of implantation, form traps, which attract the following carbon atoms. Liangdeng et al. (2008) after implantation of C ions (E = 80 keV, D = 2.7×1017 ион/cм2) in the Raman spectra observed double band with center in 1380 and 1590 cm-1 corresponding to the range of graphitized amorphous carbon. The authors suggest that since solid solubility of carbon in a-Si at a temperature close to the melting point of Si, is about 1017/cm3, and almost disappears at room temperature, the carbon has a tendency to form precipitates. Bayazitov et al. (2003) after implantation of carbon ions (E = 40 keV, D = 5*×*1017 см*−*2) in silicon and pulsed ion beam annealing (*W* = 1.0 J/cm2, C+(~80%) and H+(~20%)) have formed a β-SiC layer with an average size of grain about 100 nm. Increasing the energy density per pulse up to 1.5 J/cm2 leads also to appearance of graphite grains of sizes about 100 nm, as well as visually observed darkening of the sample. When exposed by radiation of ruby laser (λ = 0.69 μm, τ = 50 nsec, W = 0.5-2 J/cm2) also formed the graphite grains, beginning from W = 0.5 J/cm2.

The Formation of Silicon Carbide in the SiCx Layers

mechanism of the formation of SiC crystallites.

place.

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 103

1 (Fig. 25a, curves 1 and 2). Decrease in area at 1400°C is associated with a decrease in amplitude at all considered frequencies, especially at 800 cm-1, indicating that the decay of a large number of tetrahedral Si-C-bonds and desorption of ~ 15% of carbon atoms are taken

As shown in Fig. 26 **(**curve 3), the number of optically active **Si**−**C-**bonds in the temperature range 20−1200°C is the highest for the layer SiC0. 7. In the temperature range 20−1300°C, the amplitude at 800 cm-1 increases in 4.4 times from 20 to 87%, while the area of **SiC-**peak grow only in 3.76/2.45 = 1.54 times.. It follows that growth in the number of tetrahedral bonds is taken place not only due to the decay of optically inactive **Si**−**C-**clusters, but as a result of decay of long single **Si**−**C-**bonds as well, which absorb at a frequency of 700 cm-1 **(**Fig. 25c, curve 1 ), with their transformation into a tetrahedral (curve 3) and close to tetrahedral (curve 4) bonds, which absorb near 800 and 850 cm-1. Most intensively this process occurs near the surface of SiC crystallites (Fig.12b) in the range 900−1300°C showing the

The temperature dependence of both the amplitude of the IR transmission at different wave numbers and the area of SiC-peak for the SiC1.4, SiC0.95 and SiC0.7 layers has a similar character, which, as it was mentioned above, indicates the common nature of carbon and carbon-silicon clusters in these layers with a high concentration of carbon. Analysis of the behavior of the curves in Fig. 26 (curves 4, 5 and 6) shows that the curves of the area changes of the peak for the SiC-layers with low carbon concentration SiC0.4, SiC0.12 and SiC0.03 also have the maxima and minima of magnitude, which can be associated with the formation and breaking of bonds and clusters. These layers are characterized by an higher proportion (%) of carbon atoms forming an optically active Si−C-bonds (Table 5), although the total

The value of the area for the SiC0.4 layer in the temperature range 20−1400°C has not a continuous upward trend. Maximum of area at 800°C is due to the formation of tetrahedral and close to tetrahedral bonds, absorbing near 800 and 850 cm**-1 (**Fig. 25d, curves 3 and 4), respectively. The formation of tetrahedral bonds **(**800 cm-1) at temperatures of 900−1100°C **(**Fig. 25d, curve 3) is accompanied by decreasing of peak area due to its narrowing resulting from the decay of long single **Si**−**C-**bonds, which absorbed near 700 and 750 cm-1 and prevailed at temperatures below 800°C. The formation of Si and SiC crystallites in the layer is taken place almost simultaneously, which suggests intense movement of C and Si atoms and the increase in the number of dangling bonds. The increase in area in the range 1200−1300°C **(**Fig. 26) is caused by growth of tetrahedral (Fig. 25, curve 3) and close to tetrahedral **(**Fig. 25, curves 2 and 4) **Si**−**C-**bonds due to decay of optically inactive clusters. For layers SiC0.12 and SiC0.03 with carbon concentration much lower than stoichiometric for SiC, the absence of significant growth of area in the temperature range 200−1100°C is revealed due to the small amount of optically inactive unstable carbon flat nets and chains, the decay of which could cause an intensive formation of absorbing bonds. Nevertheless, a significant increase in amplitude at 800 cm**-**1 is observed due to the formation of tetrahedral bonds. Increase in the area after annealing at 900−1000°C for the SiC0.03 layer together with growth of the amplitudes of all types of optically active **Si**−**C-**bonds may be caused by the formation of silicon crystallites, which accompanied by the displacement of carbon atoms and a reduction in the number of dangling bonds of carbon atoms. For layers SiC0.12 and SiC0.4 the significant growth of area at temperatures 1200−1300°C caused by an increase in the number of all types of optically active bonds due to decay of stable carbon clusters.

number is low in comparison with SiC1.4, SiC0.95 and SiC0.7 layers (Fig. 26).

Tetelbaum et al. (2009) by implantation in SiO2 film of Si ions (E = 100 keV, D = 7×1016 cm-2) provided the concentration of excess silicon at the peak of the ion distribution about 10 at.%. Then the same number of carbon atoms was implanted. The obtained data of the white photoluminescence with bands at ~400, ~500 and ~625 nm, attributed to nanoinclusion of phases of SiC, C, nanoclusters and small nanocrystals Si, respectively (the arguments supported by references to the results of Perez-Rodrguez et al. (2003) and Fan et al. (2006)). Similarly, Zhao et al. (1998) received a peak at 350 nm, and a shifting by the annealing the blue peak at 410−440, 470, 490 nm. The existence of inclusions phases of carbon and silicon carbide in the films of SiO2 in (Tetelbaum et al., 2009) was confirmed by X-ray photoelectron spectroscopy by the presence of the C−C (with energy ~285 eV) and Si−C (with energy ~283 eV). Comparing the amplitudes IRFS one can conclude that a number of C−C is comparable to the number of Si−C-bonds, and a luminescence at 500 nm (carbon clusters) is considerably greater than the luminescence at 400 nm (silicon carbide). Belov et al. (2010) used higher doses of carbon ions (E = 40 keV): 6×1016 см-2, 9×1016 см-2 and 1.2×1017 см-2, in which the concentration of carbon (by our estimation) do not exceed 25% at the maximum of the carbon distribution. The authors believe that the luminescent centers, illuminated at wavelengths below 700 nm, represent the nanoclusters and nanocrystals of (Si:C), and amorphous clusters of diamond-like and graphitized carbon. In this case, with increasing of carbon doses the intensity of photoluminescence from Si nanocrystals (>700 nm) varies little, and concluded that a significant portion of the implanting carbon is included into the carbon clusters. The high content of graphitized clusters in the films also discussed in (Shimizu-Iwayama et al., 1994). All these data suggest that a significant or most of the carbon atoms are composed of carbon clusters, although the concentration of carbon atoms in a layer of "SiO2 + Si + C" was around 9 at.%. In our opinion, this confirms our high estimates of carbon content in the optically inactive C- and C−Si-clusters, made basing the analysis of IR spectra. Analysis of the behavior of the curves in Fig. 26 may be interesting from the point of studying the influence of decay of clusters and Si−C-bonds on the formation of tetrahedral oriented Si-C-bonds. Basing on the analysis one can suggest possible mechanisms of formation of silicon carbide grains in the layer and put forward a number of hypotheses. For example, the growth curves of SiC-peak area for the SiC1.4, SiC0.95 and SiC0.7 layers with a high carbon concentration have the maxima of values, which may be related with the formation and breaking of bonds and clusters in the implanted layer. Intensive growth of area in the range 1100−1300°C caused by the decay of stable optically inactive clusters (Table 5) and an increase in the number of all types of Si−C-bonds absorbing at all frequencies of considered range, in particular, the tetrahedral oriented bonds (800 cm-1). However, the growth of these bonds (curves 3 in Figure 25) is not always accompanied by an increase in area under the IR transmittance peak.

Variation of the peak area for the SiC1,4 layer (Fig. 26) has peaks at 400, 1000 and 1300°C. The growth of the peak area in the range of 20−800°C for SiC1.4, SiC0.95 and SiC0.7 layers with high carbon concentrations is caused by a weak ordering of the amorphous layer and the formation of optically active Si−C-bonds, including the tetrahedral oriented bonds (Fig. 25a). Significant growth of area in the range 800−1000°C is resulted by an increase of the absorption in the range 800±50 cm-1, i.e. by an intensive formation of the tetrahedral and near tetrahedral Si−C-bonds due to the decay of such optically inactive clusters as flat nets and chains (Fig. 24). Decrease of Si−C-peak area (Fig. 26, curves 1 and 3) in ranges of 400−600°C or 600−800°C caused by decay of long single bonds absorbing near 700 or 750 cm-

Tetelbaum et al. (2009) by implantation in SiO2 film of Si ions (E = 100 keV, D = 7×1016 cm-2) provided the concentration of excess silicon at the peak of the ion distribution about 10 at.%. Then the same number of carbon atoms was implanted. The obtained data of the white photoluminescence with bands at ~400, ~500 and ~625 nm, attributed to nanoinclusion of phases of SiC, C, nanoclusters and small nanocrystals Si, respectively (the arguments supported by references to the results of Perez-Rodrguez et al. (2003) and Fan et al. (2006)). Similarly, Zhao et al. (1998) received a peak at 350 nm, and a shifting by the annealing the blue peak at 410−440, 470, 490 nm. The existence of inclusions phases of carbon and silicon carbide in the films of SiO2 in (Tetelbaum et al., 2009) was confirmed by X-ray photoelectron spectroscopy by the presence of the C−C (with energy ~285 eV) and Si−C (with energy ~283 eV). Comparing the amplitudes IRFS one can conclude that a number of C−C is comparable to the number of Si−C-bonds, and a luminescence at 500 nm (carbon clusters) is considerably greater than the luminescence at 400 nm (silicon carbide). Belov et al. (2010) used higher doses of carbon ions (E = 40 keV): 6×1016 см-2, 9×1016 см-2 and 1.2×1017 см-2, in which the concentration of carbon (by our estimation) do not exceed 25% at the maximum of the carbon distribution. The authors believe that the luminescent centers, illuminated at wavelengths below 700 nm, represent the nanoclusters and nanocrystals of (Si:C), and amorphous clusters of diamond-like and graphitized carbon. In this case, with increasing of carbon doses the intensity of photoluminescence from Si nanocrystals (>700 nm) varies little, and concluded that a significant portion of the implanting carbon is included into the carbon clusters. The high content of graphitized clusters in the films also discussed in (Shimizu-Iwayama et al., 1994). All these data suggest that a significant or most of the carbon atoms are composed of carbon clusters, although the concentration of carbon atoms in a layer of "SiO2 + Si + C" was around 9 at.%. In our opinion, this confirms our high estimates of carbon content in the optically inactive C- and C−Si-clusters, made basing the analysis of IR spectra. Analysis of the behavior of the curves in Fig. 26 may be interesting from the point of studying the influence of decay of clusters and Si−C-bonds on the formation of tetrahedral oriented Si-C-bonds. Basing on the analysis one can suggest possible mechanisms of formation of silicon carbide grains in the layer and put forward a number of hypotheses. For example, the growth curves of SiC-peak area for the SiC1.4, SiC0.95 and SiC0.7 layers with a high carbon concentration have the maxima of values, which may be related with the formation and breaking of bonds and clusters in the implanted layer. Intensive growth of area in the range 1100−1300°C caused by the decay of stable optically inactive clusters (Table 5) and an increase in the number of all types of Si−C-bonds absorbing at all frequencies of considered range, in particular, the tetrahedral oriented bonds (800 cm-1). However, the growth of these bonds (curves 3 in Figure 25) is not always accompanied by an increase in

Variation of the peak area for the SiC1,4 layer (Fig. 26) has peaks at 400, 1000 and 1300°C. The growth of the peak area in the range of 20−800°C for SiC1.4, SiC0.95 and SiC0.7 layers with high carbon concentrations is caused by a weak ordering of the amorphous layer and the formation of optically active Si−C-bonds, including the tetrahedral oriented bonds (Fig. 25a). Significant growth of area in the range 800−1000°C is resulted by an increase of the absorption in the range 800±50 cm-1, i.e. by an intensive formation of the tetrahedral and near tetrahedral Si−C-bonds due to the decay of such optically inactive clusters as flat nets and chains (Fig. 24). Decrease of Si−C-peak area (Fig. 26, curves 1 and 3) in ranges of 400−600°C or 600−800°C caused by decay of long single bonds absorbing near 700 or 750 cm-

area under the IR transmittance peak.

1 (Fig. 25a, curves 1 and 2). Decrease in area at 1400°C is associated with a decrease in amplitude at all considered frequencies, especially at 800 cm-1, indicating that the decay of a large number of tetrahedral Si-C-bonds and desorption of ~ 15% of carbon atoms are taken place.

As shown in Fig. 26 **(**curve 3), the number of optically active **Si**−**C-**bonds in the temperature range 20−1200°C is the highest for the layer SiC0. 7. In the temperature range 20−1300°C, the amplitude at 800 cm-1 increases in 4.4 times from 20 to 87%, while the area of **SiC-**peak grow only in 3.76/2.45 = 1.54 times.. It follows that growth in the number of tetrahedral bonds is taken place not only due to the decay of optically inactive **Si**−**C-**clusters, but as a result of decay of long single **Si**−**C-**bonds as well, which absorb at a frequency of 700 cm-1 **(**Fig. 25c, curve 1 ), with their transformation into a tetrahedral (curve 3) and close to tetrahedral (curve 4) bonds, which absorb near 800 and 850 cm-1. Most intensively this process occurs near the surface of SiC crystallites (Fig.12b) in the range 900−1300°C showing the mechanism of the formation of SiC crystallites.

The temperature dependence of both the amplitude of the IR transmission at different wave numbers and the area of SiC-peak for the SiC1.4, SiC0.95 and SiC0.7 layers has a similar character, which, as it was mentioned above, indicates the common nature of carbon and carbon-silicon clusters in these layers with a high concentration of carbon. Analysis of the behavior of the curves in Fig. 26 (curves 4, 5 and 6) shows that the curves of the area changes of the peak for the SiC-layers with low carbon concentration SiC0.4, SiC0.12 and SiC0.03 also have the maxima and minima of magnitude, which can be associated with the formation and breaking of bonds and clusters. These layers are characterized by an higher proportion (%) of carbon atoms forming an optically active Si−C-bonds (Table 5), although the total number is low in comparison with SiC1.4, SiC0.95 and SiC0.7 layers (Fig. 26).

The value of the area for the SiC0.4 layer in the temperature range 20−1400°C has not a continuous upward trend. Maximum of area at 800°C is due to the formation of tetrahedral and close to tetrahedral bonds, absorbing near 800 and 850 cm**-1 (**Fig. 25d, curves 3 and 4), respectively. The formation of tetrahedral bonds **(**800 cm-1) at temperatures of 900−1100°C **(**Fig. 25d, curve 3) is accompanied by decreasing of peak area due to its narrowing resulting from the decay of long single **Si**−**C-**bonds, which absorbed near 700 and 750 cm-1 and prevailed at temperatures below 800°C. The formation of Si and SiC crystallites in the layer is taken place almost simultaneously, which suggests intense movement of C and Si atoms and the increase in the number of dangling bonds. The increase in area in the range 1200−1300°C **(**Fig. 26) is caused by growth of tetrahedral (Fig. 25, curve 3) and close to tetrahedral **(**Fig. 25, curves 2 and 4) **Si**−**C-**bonds due to decay of optically inactive clusters.

For layers SiC0.12 and SiC0.03 with carbon concentration much lower than stoichiometric for SiC, the absence of significant growth of area in the temperature range 200−1100°C is revealed due to the small amount of optically inactive unstable carbon flat nets and chains, the decay of which could cause an intensive formation of absorbing bonds. Nevertheless, a significant increase in amplitude at 800 cm**-**1 is observed due to the formation of tetrahedral bonds. Increase in the area after annealing at 900−1000°C for the SiC0.03 layer together with growth of the amplitudes of all types of optically active **Si**−**C-**bonds may be caused by the formation of silicon crystallites, which accompanied by the displacement of carbon atoms and a reduction in the number of dangling bonds of carbon atoms. For layers SiC0.12 and SiC0.4 the significant growth of area at temperatures 1200−1300°C caused by an increase in the number of all types of optically active bonds due to decay of stable carbon clusters.

The Formation of Silicon Carbide in the SiCx Layers

concentration of strong clusters.

glow discharge hydrogen plasma.

а)

at the temperature 900°С for 30 min (b).

0,20

0,30

0,40

0,50

**Transmittance**

0,60

0,70

minutes.

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 105

temperatures of about 100°C lower than for the layers SiC1.4, SiC0.95 and SiC0.7 due to a lower

Thus, we have shown a negative effect of stable carbon and carbon-silicon clusters on the crystallization of SiC in the layers. Heat treatment up to 1200ºC does not lead to complete disintegration of the clusters and the release of C and Si atoms to form SiC. In this regard, identification of alternative ways of processing the films to break down clusters and form a more qualitative structure of the SiC films is important. As shown in section 3.3, the characteristics of glow discharge hydrogen plasma and treatment (27.12 MHz, 12.5 W, 6.5 Pa, 100°C, 5 min) were sufficient to decay the tetrahedral Si−Si and Si−C-bonds and can be used for the destruction of stable carbon and carbon−silicon clusters. For IR analysis, the sample with the SiC0.95 film was cut into two parts and one of these samples was treated by hydrogen plasma. Fig. 28 shows the IR transmittance spectra of these SiC0.95 layers, untreated by plasma (a) and treated by hydrogen plasma (b) after annealing at 900ºC for 30

Peak maxima occur at 790 cm-1, indicating the prevalence of tetrahedral oriented Si−C-bonds characteristic of crystalline SiC. Measurements of the half-widths of the spectra in Fig. 28a, b give the magnitudes 148 and 78 cm-1 for pre-untreated and treated by hydrogen plasma SiC0.95 layer, respectively. If the value of 148 cm-1 is characteristic for the temperature range 900−1000°C (Fig. 27, curve 2), but the value of 78 cm-1, in principle, was unattainable for the SiC0.95 layer without pre-treatment by plasma throughout the temperature range 200−1400°C. Thus, we can conclude that annealing at 900°C of SiC0.95 layers, treated by hydrogen plasma with power of 12.5 watts only, has led to the formation of β-SiC crystalline layer, which superior in structure quality the untreated by plasma layer subjected to isochronous annealing in the range 200−1400°C. Obviously, the observed effects of plasmainduced crystallization is a consequence of the decay of clusters in the pre-treatment by

0,05

Fig. 28. IR transmission spectra for SiC0.95 layer after annealing at the temperature 900°С for 30 min (a) and after processing by glow discharge hydrogen plasma for 5 min and annealing

400 700 1000 1300 **Wave number, cm-1**

0,15

0,25

0,35

**Transmittance**

400 700 1000 1300 **Wave number, cm-1**

0,45

0,55

b)

The half-width of the Si−C-peak of IR transmission were measured (Fig. 27). Narrowing of the peak occurs due to intensive formation of tetrahedral oriented Si−C-bonds, absorbing at 800 cm-1, and decay of bonds, which absorb at frequencies far from the value of 800 cm-1. Since the tetrahedral bonds correspond to the crystalline phase of silicon carbide, so the narrowing of the SiC-peak of the IR spectrum is related with the processes of the implanted layer ordering. For a layer SiC1.4 a sharp narrowing of the peak from 300 to 110 cm-1 is taken place in the range 800−1200°C, and then the half-width does not change significantly. The most intensively this process occurs in the range 900−1000°C. On X-ray diffraction patterns (Fig. 7), the appearance of lines of polycrystalline β-SiC was observed after annealing at 1200°C and above. This implies that the appearance of SiC crystallites in the layer is recorded when the formation of tetrahedral bonds (peak narrowing) is substantially complete (110 cm-1). Assumptions about the relationship between the size of SiC crystallites and half-width of the peak were also expressed in (Wong et al., 1998; Chen et al., 1999). For the SiC0. 7 layer in range 900−1000°C, a sharp narrowing of the peak from 280 to 85 cm-1 is taken place and occurred more intensive up to 67 cm-1 at 1200°C than for layers with a higher carbon concentration SiC0.95 (115 cm-1, 1200°C) and SiC1.4 (108 cm-1, 1300°C), indicating a much lower concentration of strong clusters in the layer SiC0.7.

Fig. 27. Effect of the annealing temperature on the FWHM of the IR transmittance SiC-peak for TO phonons under normal incidence of IR radiation on the sample surface: 1 − SiC1.4, 2 − SiC0.95, 3 − SiC0.7, 4 − SiC0.4, 5 − SiC0.12, 6 − SiC0.03.

For a layer SiC0.12, a sharp narrowing of the peak from 240 to 100 cm-1 (Fig. 27, curve 5) in the range 800−1100°C is shown, and then is not substantially reduced, demonstrating the formation of polycrystalline SiC phase at this temperature. In general, for the SiC0.4, SiC0.12 and SiC0.03 layers with low carbon concentration a sharp narrowing of the peak occurs at

The half-width of the Si−C-peak of IR transmission were measured (Fig. 27). Narrowing of the peak occurs due to intensive formation of tetrahedral oriented Si−C-bonds, absorbing at 800 cm-1, and decay of bonds, which absorb at frequencies far from the value of 800 cm-1. Since the tetrahedral bonds correspond to the crystalline phase of silicon carbide, so the narrowing of the SiC-peak of the IR spectrum is related with the processes of the implanted layer ordering. For a layer SiC1.4 a sharp narrowing of the peak from 300 to 110 cm-1 is taken place in the range 800−1200°C, and then the half-width does not change significantly. The most intensively this process occurs in the range 900−1000°C. On X-ray diffraction patterns (Fig. 7), the appearance of lines of polycrystalline β-SiC was observed after annealing at 1200°C and above. This implies that the appearance of SiC crystallites in the layer is recorded when the formation of tetrahedral bonds (peak narrowing) is substantially complete (110 cm-1). Assumptions about the relationship between the size of SiC crystallites and half-width of the peak were also expressed in (Wong et al., 1998; Chen et al., 1999). For the SiC0. 7 layer in range 900−1000°C, a sharp narrowing of the peak from 280 to 85 cm-1 is taken place and occurred more intensive up to 67 cm-1 at 1200°C than for layers with a higher carbon concentration SiC0.95 (115 cm-1, 1200°C) and SiC1.4 (108 cm-1, 1300°C),

indicating a much lower concentration of strong clusters in the layer SiC0.7.

**1**

 **6**

 **5**

**4**

**0 200 400<PHONE_NUMBER> 1200 1400 Temperature, о**

Fig. 27. Effect of the annealing temperature on the FWHM of the IR transmittance SiC-peak for TO phonons under normal incidence of IR radiation on the sample surface: 1 − SiC1.4, 2 −

For a layer SiC0.12, a sharp narrowing of the peak from 240 to 100 cm-1 (Fig. 27, curve 5) in the range 800−1100°C is shown, and then is not substantially reduced, demonstrating the formation of polycrystalline SiC phase at this temperature. In general, for the SiC0.4, SiC0.12 and SiC0.03 layers with low carbon concentration a sharp narrowing of the peak occurs at

**2**

**С**

**3**

**50**

SiC0.95, 3 − SiC0.7, 4 − SiC0.4, 5 − SiC0.12, 6 − SiC0.03.

**100**

**150**

**200**

**FWHM of the IR transmittance SiC-peak, cm -1**

**250**

**300**

**350**

**400**

temperatures of about 100°C lower than for the layers SiC1.4, SiC0.95 and SiC0.7 due to a lower concentration of strong clusters.

Thus, we have shown a negative effect of stable carbon and carbon-silicon clusters on the crystallization of SiC in the layers. Heat treatment up to 1200ºC does not lead to complete disintegration of the clusters and the release of C and Si atoms to form SiC. In this regard, identification of alternative ways of processing the films to break down clusters and form a more qualitative structure of the SiC films is important. As shown in section 3.3, the characteristics of glow discharge hydrogen plasma and treatment (27.12 MHz, 12.5 W, 6.5 Pa, 100°C, 5 min) were sufficient to decay the tetrahedral Si−Si and Si−C-bonds and can be used for the destruction of stable carbon and carbon−silicon clusters. For IR analysis, the sample with the SiC0.95 film was cut into two parts and one of these samples was treated by hydrogen plasma. Fig. 28 shows the IR transmittance spectra of these SiC0.95 layers, untreated by plasma (a) and treated by hydrogen plasma (b) after annealing at 900ºC for 30 minutes.

Peak maxima occur at 790 cm-1, indicating the prevalence of tetrahedral oriented Si−C-bonds characteristic of crystalline SiC. Measurements of the half-widths of the spectra in Fig. 28a, b give the magnitudes 148 and 78 cm-1 for pre-untreated and treated by hydrogen plasma SiC0.95 layer, respectively. If the value of 148 cm-1 is characteristic for the temperature range 900−1000°C (Fig. 27, curve 2), but the value of 78 cm-1, in principle, was unattainable for the SiC0.95 layer without pre-treatment by plasma throughout the temperature range 200−1400°C. Thus, we can conclude that annealing at 900°C of SiC0.95 layers, treated by hydrogen plasma with power of 12.5 watts only, has led to the formation of β-SiC crystalline layer, which superior in structure quality the untreated by plasma layer subjected to isochronous annealing in the range 200−1400°C. Obviously, the observed effects of plasmainduced crystallization is a consequence of the decay of clusters in the pre-treatment by glow discharge hydrogen plasma.

Fig. 28. IR transmission spectra for SiC0.95 layer after annealing at the temperature 900°С for 30 min (a) and after processing by glow discharge hydrogen plasma for 5 min and annealing at the temperature 900°С for 30 min (b).

The Formation of Silicon Carbide in the SiCx Layers

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 107

Fig. 30. Atomic force microscopy of the surface of SiCx layers with various carbon

In Fig. 31 the AFM data on changes in surface topography of the annealed at 1400°C SiC1.4 layer before (Fig. 31a) and after (Fig. 31b and c) processing by glow discharge hydrogen plasma (27.12 MHz, 12.5 W, 6.5 Pa, 100°C, 5 min) in two various areas with sizes of 1 × 1 um2, are presented. The more increased fragments are also shown. Processing by hydrogen plasma does not lead to complete destruction of the granular structure (Fig. 31b), although in some areas granular structure significantly damaged (Fig. 31c), which correlates with the

Fig. 31. Atomic force microscopy of SiC1.4 layers after annealing at the temperature of 1400°С

(a) and subsequent processing by glow discharge hydrogen plasma for 5 min (b, c).

concentration before and after high temperature annealing

X-ray data (Fig. 7).

#### **3.5 Investigations by atomic force microscopy**

AFM studies of the surface microstructure of the surface of the SiC0.95 layer of area 500 × 500 nm2, and 1 × 1 um2 show (Fig. 29a), that after implantation, the surface of the layer looks flat with fluctuations in the height ranged within 6 nm. The areas above the average line of the surface have bright light colors and the areas below the same have dark colors, from which begins the account of height. Annealing at 800°C (Fig. 29b) leads to the deformation of the surface and to an appearance of furrows indicating an intensive translations of atoms. After annealing at 1400°C the surface consists of grains with sizes of 30−50 nm. The variations in height ranged within 66 nm. Comparison of grain sizes with X-ray data on the average crystallite sizes of SiC (3−10 nm) shows that the grains are composed of crystallites of SiC.

Fig. 29. AFM images from the surface of thin (~130 nm) SiC0.95 film (a) after multiple implantation and annealing at (b) 800°C and (c) 1400°C.

In general, we can see that after implantation the surfaces of SiC1.4, SiC0.95, SiC0.7, SiC0.4 and SiC0.12 layers looks smooth with the fluctuations of the height in range of 2−6 nm (Fig. 30). At temperatures of 800−1400°C the surface of these layers are deformed with the formation of grains with sizes of ~30−100 nm. For example, after implantation the smooth surface of SiC1.4 layer looks broken with fluctuations of the height in range of 2 nm. Annealing at 1400°C leads to a clear fragmentation of grains on the surface. It is seen that the grains with sizes of ~100 nm are composed of subgrains, which probably represent the SiC crystallites with an average size of 10 nm. The surface of SiC0.7 layer, after annealing at 1250ºC for 30 minutes, consists of granules of a size of 50−100 nm and flat areas.

Amorphous after implantation, the surface structure of the SiC0.4 layer is also transformed after annealing at 1200ºC for 30 minutes and forms a granular structure consisting of spherical grains of Si and SiC with sizes of ~ 50−100 nm, which suggests an intensive movements of atoms in this layer at high temperature due to the lower content of stable clusters in the film. The surface of the SiC0.12 layer after annealing at 1400°C consists of grains with sizes of 50 nm. The smooth surface of SiC0.03 layer is recrystallized at 1250°C and contains evenly distributed inclusions of SiC in the form of point protrusions with a diameter of 20 nm (Fig. 30).

AFM studies of the surface microstructure of the surface of the SiC0.95 layer of area 500 × 500 nm2, and 1 × 1 um2 show (Fig. 29a), that after implantation, the surface of the layer looks flat with fluctuations in the height ranged within 6 nm. The areas above the average line of the surface have bright light colors and the areas below the same have dark colors, from which begins the account of height. Annealing at 800°C (Fig. 29b) leads to the deformation of the surface and to an appearance of furrows indicating an intensive translations of atoms. After annealing at 1400°C the surface consists of grains with sizes of 30−50 nm. The variations in height ranged within 66 nm. Comparison of grain sizes with X-ray data on the average crystallite sizes of SiC (3−10 nm) shows that the grains are

> **250 [nm]**

implantation and annealing at (b) 800°C and (c) 1400°C.

minutes, consists of granules of a size of 50−100 nm and flat areas.

Fig. 29. AFM images from the surface of thin (~130 nm) SiC0.95 film (a) after multiple

In general, we can see that after implantation the surfaces of SiC1.4, SiC0.95, SiC0.7, SiC0.4 and SiC0.12 layers looks smooth with the fluctuations of the height in range of 2−6 nm (Fig. 30). At temperatures of 800−1400°C the surface of these layers are deformed with the formation of grains with sizes of ~30−100 nm. For example, after implantation the smooth surface of SiC1.4 layer looks broken with fluctuations of the height in range of 2 nm. Annealing at 1400°C leads to a clear fragmentation of grains on the surface. It is seen that the grains with sizes of ~100 nm are composed of subgrains, which probably represent the SiC crystallites with an average size of 10 nm. The surface of SiC0.7 layer, after annealing at 1250ºC for 30

Amorphous after implantation, the surface structure of the SiC0.4 layer is also transformed after annealing at 1200ºC for 30 minutes and forms a granular structure consisting of spherical grains of Si and SiC with sizes of ~ 50−100 nm, which suggests an intensive movements of atoms in this layer at high temperature due to the lower content of stable clusters in the film. The surface of the SiC0.12 layer after annealing at 1400°C consists of grains with sizes of 50 nm. The smooth surface of SiC0.03 layer is recrystallized at 1250°C and contains evenly distributed inclusions of SiC in the form of point protrusions with a

**(a) (b) (c)**

**250 [nm]**

**3.5 Investigations by atomic force microscopy**

composed of crystallites of SiC.

**250 [nm]**

diameter of 20 nm (Fig. 30).

Fig. 30. Atomic force microscopy of the surface of SiCx layers with various carbon concentration before and after high temperature annealing

In Fig. 31 the AFM data on changes in surface topography of the annealed at 1400°C SiC1.4 layer before (Fig. 31a) and after (Fig. 31b and c) processing by glow discharge hydrogen plasma (27.12 MHz, 12.5 W, 6.5 Pa, 100°C, 5 min) in two various areas with sizes of 1 × 1 um2, are presented. The more increased fragments are also shown. Processing by hydrogen plasma does not lead to complete destruction of the granular structure (Fig. 31b), although in some areas granular structure significantly damaged (Fig. 31c), which correlates with the X-ray data (Fig. 7).

Fig. 31. Atomic force microscopy of SiC1.4 layers after annealing at the temperature of 1400°С (a) and subsequent processing by glow discharge hydrogen plasma for 5 min (b, c).

The Formation of Silicon Carbide in the SiCx Layers

transition "film − substrate".

~20 nm.

**5. Acknowledgement**

**6. References**

(x = 0.03–1.4) Formed by Multiple Implantation of C Ions in Si 109

4. The regularities of changes in the surface structure of the SiCx layers (x = 0.03−1.4) with the increase of temperature are revealed. At temperatures of 800−1400°C the surface layers are deformed with the formation of grains with sizes of ~30−100 nm, consisting of crystallites, and the recrystallized at 1250°C smooth surface of SiC0.03 layer contains evenly distributed Si:C inclusions in the form of point protrusions with a diameter of

5. Size effects were revealed, which manifested in the influence of the crystallite sizes of silicon carbide on its optical properties. The differences of the SiC0.03, SiC0.12 and SiC0.4 layers with low carbon concentration from the SiC1.4, SiC0.95 and SiC0.7 layers with high carbon concentration are manifested in the absence of LO-phonon peak of SiC in the IR transmission spectra and in a shift at 1000°C of minimum SiC-peak for TO phonons in the region of wave numbers higher than 800 cm-1 characteristic for the tetrahedral bonds of crystalline SiC, which is caused by small sizes of SiC crystallites (≤ 3 nm) and by an increase of contribution in the IR absorption of their surfaces, and the surfaces of

6. The estimations of the proportion of carbon atoms that form clusters in the SiCх layers are evaluated. At 1300°C in the SiC1.4 layer only ~9% of C atoms form the optically active Si−C-bonds, in SiC0.95 − 12%, in SiC0.7 and SiC0.4 − 16%, in SiC0.12 − 45%, while the remaining carbon atoms are included in composition of stable clusters. The total number N of formed Si−C-bonds in SiCx layers was growing with a fractional power of carbon concentration x: N = а·(n1)y, where y ≈ 0.37±0.09, n1= х/0.03, а = const. 7. It was shown that processing by hydrogen glow discharge plasma (27.12 MHz, 12.5 W, 6.5 Pa, 100°C, 5 min) of polycrystalline SiC1.4 layer leads to partial disintegration of β-SiC crystallites in layer and complete decay of Si crystallites in the transition layer "film−substrate" ("SiC−Si"). Processing by plasma and annealing at 900°C of SiC0.95 layer has led to the formation of β-SiC crystalline layer, which superior in structure quality the untreated by plasma layer subjected to isochronous annealing in the range 200−1400°C. Phenomenon of plasma-induced crystallization is a consequence of the

decay of clusters during pre-treatment by glow discharge hydrogen plasma.

The authors are very grateful to Mukhamedshina D.M. for processing the samples by glow

Akimchenko, I.P., Kisseleva, K.V., Krasnopevtsev, V.V., Milyutin, Yu.V., Touryanski, A.G.,

Akimchenko, I.P., Kazdaev, H.P., Krasopevtsev, V.V. (1977). IK-pogloshenie β-SiC,

silicon by ion implantation. Radiation Effects, Vol. 33., pp.75–80.

Vavilov, V.S. (1977). The structure of silicon carbide synthesized in diamond and

sintezirovannogo pri ionnoi implantacii C v Si. Fizika i Tekhnika Poluprovodnikov,

Si crystallites containing strong short Si−C-bonds as well.

discharge hydrogen plasma and Mit' K.A. for AFM measurements.

T.11, vyp. 10., pp.1964-1966 (in Rusiian).

Si−C-clusters, is consisted of Si crystallites with average size ~25 nm, 25% of the volume − β-SiC crystallite with size of ~5 nm and 25% − the c-Si recrystallized near the

Fig. 32a, b shows the surface areas of the untreated by hydrogen plasma SiC0.95 film after annealing at 900°C, which have a granular structure and consist of grains with sizes within ~50−250 nm. On the enlarged fragments one can also see the flat areas which can be associated with the amorphous component. Surface after treatment by glow discharge hydrogen plasma for 5 min and annealing at 900°C has a more developed granular structure (Fig. 32c, d) and consist of grains with sizes within ~150−400 nm. These results correlate with the IR spectroscopy data (Fig. 28).

Fig. 32. Atomic force microscopy of SiC0.95 layer: (a, b) after synthesis and annealing at the temperature of 900°С for 30 min; (c, d) after synthesis, processing by glow discharge hydrogen plasma for 5 min and annealing at 900°С for 30 min.

#### **4. Conclusion**

Fig. 32a, b shows the surface areas of the untreated by hydrogen plasma SiC0.95 film after annealing at 900°C, which have a granular structure and consist of grains with sizes within ~50−250 nm. On the enlarged fragments one can also see the flat areas which can be associated with the amorphous component. Surface after treatment by glow discharge hydrogen plasma for 5 min and annealing at 900°C has a more developed granular structure (Fig. 32c, d) and consist of grains with sizes within ~150−400 nm. These results correlate

Fig. 32. Atomic force microscopy of SiC0.95 layer: (a, b) after synthesis and annealing at the temperature of 900°С for 30 min; (c, d) after synthesis, processing by glow discharge