**4.3 Role of angiotensin II, hypertension and hyperfiltration**

With progression of kidney disease the afferent arteriole tone decreases to a much larger extent than the efferent tone. As a result intra-glomerular pressure rises leading to hyperfiltration. Angiotensin II aides in hyperfiltration through its vasoconstrictor effect predominantly on the efferent arteriole. Apart from its hemodynamic effects, Angiotensin II acts directly on the glomerular membrane. It acts on the angiotensin II receptors on the surface of the podocytes, altering their permselective property, by contracting the foot processes. This allows proteins to escape in the urinary space.

Angiotensin II also induces proliferation ofglomerular cells and fibroblasts. It acts on AT1 receptors on tubular cells causing hypertrophy, which results in increased synthesis of collagen type IV. It increases macrophage activation and phagocytosis responsible for the inflammatory component associated with CKD.


**2.1. Low-***k* **materials**

The dielectric constant of materials can be typically described by Clausius-Mossotti Equation [16]:

$$\frac{k-1}{k+2} = \frac{4\pi N}{3}\,\alpha\tag{1}$$

The silica-based low-*k* materials have been successfully integrated in a microprocessor due to high chemical and thermal stability. The silica-based materials have the tetrahedral basic

oxygen atoms and each oxygen atom is bonded to two silicon atoms (SiO4/2). Each silicon atom

The first-generation low-*k* material in semiconductor production line was fluorinated silicon glass (FSG or SiOF), in which the Si–O bond is replaced by the less polarizable Si–F bond. FSG materials were used at the 0.18 μm technology node with the dielectric constant from 3.5 to

Next, the second-generation low-*k* material was the organosilicate glass (SiCOH), in which

ture. So, SiCOH materials were successfully integrated in some 130 nm and 90 nm products [23, 24]. Generally, FSG and SiCOH materials were deposited by plasma-enhanced chemical vapor deposition (PECVD). Moreover, both fluorine and carbon increase the interatomic distances or "free volume" of silica. This provides an additional decrease of dielectric constant

The limitation of *k* value for SiCOH materials is ~2.6. To prevent or limit an increase in the BEOL capacitance in the advanced technology nodes (65 nm or below), it requires a new low-*k* material with a further lower*-k* value (< 2.5). To meet this goal, the introduction of porosity in the low-*k* SiCOH materials is required because air can provide the minimum *k* value of ~1.0. The produced low-*k* material is a so-called porous SiCOH dielectric, which can be fabricated either by the structural or the subtractive method [25–27]. The latter method is widely accepted because the produced film is more thermally stable and can provide

is at the center of a regular tetrahedron of oxygen atoms.

3.8, depending on the concentration of Si–F bond [21, 22].

the Si–O bond is replaced by the less polarizable Si–CH3

but decreases the film density. Since the CH3

SiCOH materials have a lower density (~1.2–0.4 g/cm3

rial is in the range of 2.6–3.0, depending on the number of CH3

. Silica has a molecular structure, in which each Si atom is bonded to four

bond. The *k* value of the SiCOH mate-

Plasma Damage on Low-*k* Dielectric Materials http://dx.doi.org/10.5772/intechopen.79494 293

group has a larger volume and is hydrophilic,

) and tend to be hydrophilic.

groups built into the struc-

structure of SiO2

**Table 1.** Low-*k* dielectric classification.

where *k* = ε/ε0 , ε, and ε0 are the dielectric constants of the material and vacuum, *N* is the number of molecules per unit volume (density), and *α* is the total polarizability, including electronic (αe ), distortion (αd), and orientation (αo ) polarizabilities. According to Eq. (1), the dielectric constant of materials can be reduced by two strategies: decreasing the total polarizability (*α*) and density (*N*). Reducing the polarizability can be achieved by the use of low polar bonds (like C–C, C–H, Si–CH3 , etc.), and reducing the film's density can be obtained by means of the introduction of porosity. **Table 1** summarizes the classification of low-*k* materials and their corresponding dielectric constants.

Low-*k* materials can be divided into several categories: silica-based, silsesquioxane (SSQ) based, organic polymers, and amorphous carbon low-*k* materials [17–20]. The last three categories have integration issue due to the weak mechanical strength; therefore, they are not officially production in the semiconductor industry.

**Table 1.** Low-*k* dielectric classification.

In order to slow down the increase of *RC* delay, the introduction of new materials to the back-end-of-line (BEOL) interconnects is needed. Aluminum (Al) had been replaced by copper (Cu) as a conductor dielectric because Cu can provide a lower resistivity (ρ) [7]. In the case

Additionally, the integration method for Cu/low-*k* interconnects must be changed because Cu etching is very challenging due to nonvolatile by-products. Traditional metal etching approach had been replaced by a damascene process [11]. In a damascene process, plasma technology is widely used because it can provide an isotropic process and a fast rate. Thus, these changes make the low-*k* materials to direct contact with the plasma, such as dielectric etching, photo strip, barrier metal deposition, and surface treatment. Under the plasma irradiation, low-*k* materials are sensitive to chemical modification, resulting in an increased *k* value. This is so-called plasma damage [12–15], becoming the main impediment to a success-

In this connection, this chapter is an attempt to provide an overview of plasma damage on the low-*k* materials. This chapter is organized as follows: in Section 3, we introduce the low-*k* materials and plasma. Next, in Section 5, the processing with plasma damage on the low-*k* materials during interconnects fabrication is identified. Then, in Section 4, the results of plasma damage on the low-*k* materials based on our group's investigation are summarized.

The dielectric constant of materials can be typically described by Clausius-Mossotti Equation

*k* + 2 = \_\_\_\_ 4*N*

number of molecules per unit volume (density), and *α* is the total polarizability, including

dielectric constant of materials can be reduced by two strategies: decreasing the total polarizability (*α*) and density (*N*). Reducing the polarizability can be achieved by the use of low polar

of the introduction of porosity. **Table 1** summarizes the classification of low-*k* materials and

Low-*k* materials can be divided into several categories: silica-based, silsesquioxane (SSQ) based, organic polymers, and amorphous carbon low-*k* materials [17–20]. The last three categories have integration issue due to the weak mechanical strength; therefore, they are not

materials with the relative dielectric constant (*k*) lower than 4.0 (SiO2 *k* value) [8–10].

dielectric had been replaced by the low-*k*

3 *α* (1)

) polarizabilities. According to Eq. (1), the

are the dielectric constants of the material and vacuum, *N* is the

, etc.), and reducing the film's density can be obtained by means

of the interconnecting insulator, the traditional SiO2

292 Plasma Science and Technology - Basic Fundamentals and Modern Applications

ful integration of low-*k* materials into ICs.

Finally, short conclusion is provided in Section 5.

**2. Low-***k* **materials and plasma**

\_\_\_ *k* − 1

), distortion (αd), and orientation (αo

, ε, and ε0

their corresponding dielectric constants.

officially production in the semiconductor industry.

bonds (like C–C, C–H, Si–CH3

**2.1. Low-***k* **materials**

where *k* = ε/ε0

electronic (αe

[16]:

The silica-based low-*k* materials have been successfully integrated in a microprocessor due to high chemical and thermal stability. The silica-based materials have the tetrahedral basic structure of SiO2 . Silica has a molecular structure, in which each Si atom is bonded to four oxygen atoms and each oxygen atom is bonded to two silicon atoms (SiO4/2). Each silicon atom is at the center of a regular tetrahedron of oxygen atoms.

The first-generation low-*k* material in semiconductor production line was fluorinated silicon glass (FSG or SiOF), in which the Si–O bond is replaced by the less polarizable Si–F bond. FSG materials were used at the 0.18 μm technology node with the dielectric constant from 3.5 to 3.8, depending on the concentration of Si–F bond [21, 22].

Next, the second-generation low-*k* material was the organosilicate glass (SiCOH), in which the Si–O bond is replaced by the less polarizable Si–CH3 bond. The *k* value of the SiCOH material is in the range of 2.6–3.0, depending on the number of CH3 groups built into the structure. So, SiCOH materials were successfully integrated in some 130 nm and 90 nm products [23, 24]. Generally, FSG and SiCOH materials were deposited by plasma-enhanced chemical vapor deposition (PECVD). Moreover, both fluorine and carbon increase the interatomic distances or "free volume" of silica. This provides an additional decrease of dielectric constant but decreases the film density. Since the CH3 group has a larger volume and is hydrophilic, SiCOH materials have a lower density (~1.2–0.4 g/cm3 ) and tend to be hydrophilic.

The limitation of *k* value for SiCOH materials is ~2.6. To prevent or limit an increase in the BEOL capacitance in the advanced technology nodes (65 nm or below), it requires a new low-*k* material with a further lower*-k* value (< 2.5). To meet this goal, the introduction of porosity in the low-*k* SiCOH materials is required because air can provide the minimum *k* value of ~1.0. The produced low-*k* material is a so-called porous SiCOH dielectric, which can be fabricated either by the structural or the subtractive method [25–27]. The latter method is widely accepted because the produced film is more thermally stable and can provide a lower-*k* value. In the subtractive method, the films are deposited as a dual-phase material, using a mixture of a SiCOH skeleton precursor with an organic porogen precursor. The popularly used skeleton precursor is diethoxymethylsilane (DEMS). The used organic porogen precursor must have sufficient volatility for easy removal. The used molecules are alpha-terpinene (ATRP), bicycloheptadiene (BCHD), or cyclooctane (C8 H16). Hence, in order to remove the labile organic fraction in the as-deposited films, curing process has to be done after the deposition [8, 10, 27]. By this way, a porous film can be formed. Thermal curing, electron beam, or ultraviolet (UV) irradiation can be used to achieve this work. Generally, UV-assisted curing for the fabrication of porous SiCOH dielectrics is widely adopted by the semiconductor industry because it can also rearrange the film's structure and enhance the cross-linking of the skeleton. This provides a big help to improve the mechanical strength for porous SiCOH dielectrics.

In the ICP systems, there are two applied RF power: one is source power (top power), and the other is bias power (bottom power). Therefore, plasma density and ion energy can be controlled separately. Additionally, the ICP system has the highest plasma density with 1011–1012

has the lowest plasma density. Due to anisotropic etching property provided by ion bombardment, ICP and CCP systems are usually used for pattern etching. Since dielectric films are very sensitive to ion bombardment and ICP reactors lack passivating species required by typical dielectric etching, CCP reactors are mostly used for dielectric patterning etching. On the other hand, ICP reactors are often used for conductor patterning etching due to the etching rate consideration. To avoid damage by ion bombardment and UV light irradiation or no need anisotropic etching in the plasma process, RP reactors are the best choice. So, cleaning and resist stripping processes during semiconductor fabrication can be done by RP reactors.

The plasma-induced damage on the low-*k* dielectrics is a complex phenomenon involving both physical and chemical effects. Ion bombardment on the low-*k* dielectrics represents the physical effect. This effect depends on the energy distribution and flux for each ionic species. The chemical effect involves photochemistry induced by the UV radiation and chemical reaction between the radicals and low-*k* constituents. Under physical and chemical reactions in the plasma, the surface of low-*k* dielectrics is modified. The modification depth is related to the ion energy, diffusion of active radicals (O, H, F, etc.), and porosity and constituents in the

The plasma damage on low-*k* dielectrics makes the increase of the dielectric constant, the changes in bonding configuration, the formation of carbon-depleted layer, film shrinkage,

The depletion of carbon is mainly caused by active radicals through chemical reactions. Due

and adsorbs moisture. Therefore, a drastically increase in the *k* value and leakage current and a degradation in the dielectric breakdown were detected for plasma-treated low-*k* dielectrics.

method was also changed. "Damascene" process has been used to fabricate Cu/low-*k* interconnects because Cu cannot be easily patterned by reactive ion etching (RIE) due to the low volatility of Cu etching by-products, such as Cu chlorides and Cu fluorides [34]. Generally, "dual-damascene" process, in which both via and trench are patterned simultaneously, is widely used. The sequence of via and trench patterning can be changed. Via-first dualdamascene process, in which via is first patterned, is preferred [35]. The process flow of via-

interconnects had been transferred to Cu/low-*k* interconnects, the fabrication

**3. Low-***k* **plasma damage during interconnects fabrication**

first dual damascene is plotted step by step, as shown in **Figure 1**.

groups, the surface of low-*k* dielectrics becomes hydrophilic

–1010 electrons/cm3

Plasma Damage on Low-*k* Dielectric Materials http://dx.doi.org/10.5772/intechopen.79494

. The RP system

295

[31]. The plasma density of CCP system is 109

electrons/cm3

**2.3. Plasma damage mechanism**

low-*k* material [32, 33].

and surface densification.

As Al/SiO2

to the loss of hydrophobic CH3

The *k* value of porous SiCOH dielectrics can be scaling down by increasing the porosity and pore size simultaneously. However, this makes materials to become softer. Moreover, both the dielectric breakdown field and leakage current are degraded. Furthermore, as the porosity or pore size increases to a critical value, the pores can be connected each other to form socalled open pores. The open pores can be served as the easier penetration path into the bulk of the low-*k* material for active reactants [28]. Thus, more challenges will be addressed as porous SiCOH dielectrics are integrated in the advanced technology nodes.


**Author details**

Amor Escoz-Roldán1 \*, Pablo Ángel Meira-Cartea2 and José Gutiérrez-Pérez1

1 University of Granada, Spain

2 University of Santiago de Compostela, Spain

\*Address all correspondence to<EMAIL_ADDRESS>
© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Social Representation of Climate Change among Young Spanish University Students DOI: http://dx.doi.org/10.5772/intechopen.98258*


**4. Safety and environmental concerns about magnesium**

There are two primary sources of direct and indirect pollutant emissions in the magnesium industry. The first source is correlated to high reactivity with the oxygen of


**About the Editors**

#### **Antonio Simone Lagan`a**

Medical Doctor at the Department of Obstetrics and Gynecology, "Filippo Del Ponte" Hospital, University of Insubria, Varese, Italy.

Antonio Simone Lagana is Deputy of the Special Interest Group for Endometriosis & ` Endometrial Disorders (SIGEED) of the European Society of Human Reproduction and Embryology (ESHRE) and Ambassador of the World Endometriosis Society (WES).

His research interests include endometriosis, reproductive immunology, infertility, gynaecological endocrinology, laparoscopy, and hysteroscopy. He is the author of more than 300 papers published in PubMed-indexed international peer-reviewed journals, and his presence is often requested as an invited speaker at international congresses. He is currently an editor of high-impact journals, including Scientific Reports, PLOS One, Journal of Minimally Invasive Gynecology, Journal of Ovarian Research, Gynecologic and Obstetric Investigation, and many others.

He is habilitated as Associate Professor in Italy for Gynecology and Obstetrics.

#### **Valentina Lucia La Rosa**

Valentina Lucia La Rosa is a psychologist and is specialized in Psychotherapy. She is a Ph.D. student at the Department of Educational Sciences of the University of Catania. She is a member of several prestigious scientific societies including Italian Association of Psychology (AIP); Lacanian School of Psychoanalysis (SLP); World Association of Psychoanalysis (WAP); European Society of Human Reproduction and Embryology (ESHRE); Italian Society of Human Reproduction (SIRU); and Italian Society of Andrology and Sexual Medicine (SIAMS). Her main research interests are currently trauma and psychological well-being at different stages of development and during the COVID-19 pandemic.


1. Introduction

Since the late 1800s, human intervention has significantly altered the structure of Elkhorn Slough, and the circulation within it. Before 1946, Elkhorn Slough (ES) was a sluggish backwater with little influence from Monterey Bay. In 1946, the Army Corps of Engineers created Moss Landing Harbor located at the head of Monterey Submarine Canyon by cutting through the dune barrier that separated the Slough from Monterey Bay. ES is now a shallow, tidally-forced embayment that is directly coupled to Monterey Bay. Increased tidal action has led to a dramatic increase in tidal scouring, particularly in the lower part of the Slough [1]. The Slough was transformed from a fresh water, brackish environment to one that is primarily saltwater, and from an estuary that was primarily depositional to one that is now dominated by erosion. Since 1971, maximum tidal currents in the main channel at the mouth have increased from approximately 75 to 150 cm/s. The flood tide introduces relatively clear water from Monterey Bay while waters discharged during the ebb are laden with sediment eroded from the banks and bottom of the

Slough. This discharge creates a plume that extends 3 km or more offshore and is clearly visible in satellite imagery [2]. As erosion continues, the tidal prism and currents in ES increase, leading to further erosion. This behavior suggests a system with positive feedback, a situation that can become unstable.

Recent estimates of the erosional sediment losses from the Slough have ranged from 3.5 104 m3 /year [3] to 8 104 m3 /year [4]. Observations of bank erosion indicate average losses of 40 cm/year [5]. Bank erosion has widened the main channel, and the resulting increased tidal prism has led to an expanding network of tidal creeks that feed into the Slough (John Oliver, personal communication). According to Malzone and Kvitek [6], the tidal prism increased by 43% during the last decade and the surface area covered by salt water increased by 48%. Based on aerial surveys, losses to the surrounding wetlands (composed primarily of Salicornia marsh) have increased significantly over the past 50 years [7]. Erosion has led to an overall loss in vegetated marsh around the Slough that was most apparent during the first decade following the opening of Moss Landing Harbor.

Many environmental factors such as loss of Salicornia marsh, ichthyoplankton abundance, nutrient distributions, phytoplankton distributions, pesticide accumulation, and changes in biodiversity are related directly, or indirectly, to the circulation and physical properties of ES. According to Dyer [8], the physical, chemical, biological, and geological systems within a given estuary are, to a large extent, inseparable. Less is known about the physical environment of ES than perhaps some of its other defining properties. This is due in part to the spatial and temporal complexities of the circulation, and the rate at which physical changes to the system are occurring.

It is our purpose to summarize what is known about the tides, the circulation, and the physical properties of ES, based on a period of data collection that began in 1970 and continued into the early 2000s. In this regard, the manuscript is a period piece that spans a recent 30-year period. The work contained herein is based on the work of the first author's students, M.S. theses by some of these students, and, importantly, new observations. The text covers (1) the physical setting of the Slough, (2) the tides, (3), the physical properties, and finally, (4) the conclusions. This manuscript is based primarily on information that was contained in an unpublished report by Broenkow and Breaker [9]. However, a number of significant refinements have been made to that report which are included here for the first time.