at first , a method of synthesizing a resin used in the present invention and a first compound that generates an acid by the irradiation of actinic ray are shown as synthesis examples 1 - 3 . materials shown in table 1 are charged in a separable flask equipped with a stirrer , condenser and a thermometer , the separable flask is immersed in an oil bath and kept at an internal temperature of 97 ° c ., and polycondensation is conducted while stirring for three hours . subsequently , the internal temperature is raised to 180 ° c . and , at the same time , the pressure in the separable flask is reduced to 10 - 20 mmhg , to remove unreacted phenols , formaldehyde , water and oxalic acid . then , the molten resin is poured into a metal bat to recover cresol novolac resin . twenty grams of poly ( p - vinyl phenol ) ( trade name : linker m , manufactured by maruzen sekiyu co .) and 300 ml of ethyl acetate are charged in a separable flask equipped with a stirrer and dissolved under stirring at a room temperature ( 25 ° c .). then , 105 g of 3 , 4 - dihydro2h - pyran and 0 . 5 ml of 12n hydrochloric acid are added , stirred at a room temperature for one hour and then left to stand at a room temperature . then , 160 ml of an aqueous 2 . 38 wt % solution of tetramethyl ammonium hydroxide is added and stirred thoroughly and then an organic layer is taken out . after washing the obtained solution of the organic layer three times each time with 300 ml of distilled water , the organic layer is dried and condensed by an evaporator . 500 ml of petroleum ether is added to 50 ml of the condensed solution to conduct reprecipitation . after repeating the reprecipitation twice , reaction products are dried in a vacuum drier ( 3 mmhg , 40 ° c .) for 8 hours to obtain 22 g of poly ( p - vinylphenyl ) in which tetrahydropyranyl groups are reacted with hydroxyl groups . 25 g of silver trifluoromethane sulfonate is added to 200 ml of tetrahydrofuran , to which 20 g of trimethyl sulfonium iodide is added and stirred . after reacting them at a room temperature for about one day , precipitated silver iodide is separated by filtration . when the liquid filtrate is condensed and thus obtained crude products are recrystallized by using ethanol , 17 g of trimethylsulfoniomethane sulfonate , is obtained . after dissolving 92 wt % of the resin i obtained in synthesis example 1 , 8 wt % of poly ( p - vinylphenol ) protected by ultrahydropyral groups obtained in synthesis example 2 , 5 wt % of trimethylsulfoniotrifluoromethane sulfonate obtained in synthesis example 3 as a compound that generates the acid by irradiation of actinic ray and 0 . 1 wt % of trimethyl sulfonium iodide as an ion dissociative compound into 300 wt % of methyl cellosolve acetate , they are filtered by using a membrane filter of 0 . 1 μm pore size , to prepare a resist solution . the obtained resist solution is coated on a silicon wafer and subjected to a heat treatment at 120 ° c . for 10 min to obtain a resist film of 1 . 0 μm thickness . after exposure of the hole pattern to the resist film by using an electron - beam lithography system under conditions at an acceleration voltage of 50 kv and with an irradiation dose of 3 . 5 μc / cm 2 , it is heated at 100 ° c . for 10 min to further increase the solubility of a latent image area formed on the resist film to an aqueous alkali solution . then , the resist film is developed for 90 sec by using an aqueous 2 . 38 wt % solution of tetramethyl ammonium hydroxide as a developer , to form a positive resist pattern . as a result of electron microscopic observation for the cross sectional shape of the thus formed hole pattern of 0 . 4 μm diameter , the resist pattern had a rectangular cross sectional shape and is excellent no substantial side etching . further , decrease in the film thickness after development is less than 0 . 02 μm and it is sufficient . after preparing and then storing the resist material at 25 ° c . for one month , when the resist pattern is formed in the same manner , sufficient patterns could be formed quite in the same manner as above . the decrease in the film thickness did not change as 0 . 02 μm and it is sufficient . a positive type resist is prepared and a resist pattern is formed in the same manner as in example 1 except for using 0 . 1 wt % of ammonium acetate instead of trimethyl sulfonium iodide as the ion dissociative compound in example 1 . when the resist pattern is formed by using a resist just after preparation and a resist prepared and then stored at 25 ° c . for one month respectively , sufficient resist patterns of rectangular cross sectional shape are formed in both of the cases like that in example 1 . further , the decrease in the film thickness after development is less than 0 . 02 μm and it is sufficient . a positive type resist is prepared and a resist pattern is formed in the same manner as in example 1 except for using a tri - substituted ester of pyrogallol and methane sulfonic acid ( trade name : pyrogallol trimethylate , manufactured by midori kagaku co .) instead of trimethylsulfoniotrifluoro methane sulfonate as a compound forming an acid by irradiation of actinic ray in example 1 . when the resist pattern is formed by using a resist just after preparation and a resist prepared and then stored at 25 ° c . for one month respectively , sufficient resist patterns of rectangular cross sectional shape are formed in both of the cases like that in example 1 . further , the decrease in the film thickness after development is less than 0 . 02 μm and it is sufficient . a resist solution is prepared by dissolving 100 wt % of the resin i obtained in the synthesis example 1 , 25 wt % of 1 - hydroxy - 4 - bromo - 2 - bromoacetyl naphthalene , 15 wt % of amino resin ( cymel 303 , manufactured by mitsui cyanamide co . ), and 0 . 1 wt % of trimethyl sulfonium iodide as an ion dissociative compound into 400 wt % of propylene glycol monomethyl ether acetate , and then filtering the solution by using a membrane filter of 0 . 1 μm pore size . the obtained resist solution is coated on the surface of a silicon wafer and subjected to a heat treatment at 100 ° c . for 10 min to obtain a resist film of 1 . 0 μm thickness . a line and space pattern is formed to the resist film by using an electron - beam lithography system under conditions at an acceleration voltage of 50 kv and with an irradiation dose of 7 μc / cm 2 , it is heated at 90 ° c . for 10 min to further decrease the solubility of a hidden image area formed on the resist film to an aqueous alkali solution . after being heated , the resist film having the latent images formed thereon is developed for 300 sec by using an aqueous 2 . 38 wt % solution of tetramethyl ammonium hydroxide as a developer , to obtain negative resist patterns . as a result of electron microscopic observation for the cross sectional shape of 0 . 4 μm of line and space pattern thus formed , the resist pattern had a rectangular cross sectional shape and it is excellent . further , the decrease in the film thickness after development is as less than 0 . 05 μm and it is sufficient . after preparing and then storing the resist at 25 ° c . for one month , when the resist patterns are formed in the same manner , sufficient patterns can be formed quite in the same manner . the decrease in the film thickness did not changes as 0 . 05 μm and it is confirmed that the storability of the resist film is sufficient . a positive type resist is prepared and a resist pattern is formed by the same treatment as in example 1 except for not adding the ion dissociative compound in example 1 . as a result , although the decrease in the film thickness after development is sufficient as 0 . 02 μm just after the preparation of the resist , the cross sectional shape of the hole patterns are not rectangular but pot - like configuration , with remarkable side etching being observed . further , after storing at 25 ° c . for one month after preparation , the decrease in the film thickness after development is 0 . 5 μm and the stability is poor . a negative type resist is prepared and resist patterns are formed by the same treatment as in example 4 except for not adding the ion dissociative compound in example 4 . as a result , although the decrease in the film thickness is sufficient as 95 %, the cross sectional shape of 0 . 4 μm of line and space patterns are not rectangular but conversely tapered , with remarkable side etching being observed . further , after preparation and storing of the resist at 25 ° c . for one month , 0 . 4 μm of line and space pattern could not be resolved and the stability is poor . as apparent from the foregoing explanation , according to the present invention , it is possible to obtain a photosensitive resin composition forming a positive or negative type resist developed with an alkali solution , which has high sensitivity , high resolution capability and satisfactory stability . when actinic ray ( ultraviolet light , deep ultraviolet light , electron beams , x - rays , etc .) is irradiated to the resist film by using the photosensitive resin composition and developed by an aqueous alkali solution , a satisfactory resist pattern having a rectangular cross sectional shape with no substantial side etching can be obtained .