Abstract:
A pattern formation material of this invention contains a base polymer including a first unit represented by Chemical Formula 1 and a second unit represented by Chemical Formula 2, and an acid generator:                            
     wherein R 1  and R 2  are the same or different and selected from the group consisting of a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group and an alkyl group including a fluorine atom; 
     R 3  is a protecting group released by an acid; 
     m is an integer of 0 through 5; and 
     a and b satisfy 0&lt;a&lt;1,0&lt;b&lt;1 and 0&lt;a+b≦1.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a pattern formation method and a pattern formation material, and more particularly, it relates to a pattern formation method for forming a resist pattern, used for forming a semiconductor device or a semiconductor integrated circuit on a semiconductor substrate, by using exposing light of a wavelength not longer than a 180 nm band and a pattern formation material used in the pattern formation method. 
     Currently, in fabrication of a mass storage semiconductor integrated circuit, such as a 64 Mbit dynamic random access memory (DRAM) and a logic device or a system LSI with a 0.25 μm through 0.15 μm rule, a resist pattern is formed by using a chemically amplified resist material including a polyhydroxystyrene derivative and an acid generator as principal constituents with KrF excimer laser (of a wavelength of a 248 nm band) used as exposing light. 
     Moreover, for fabrication of a 256 Mbit DRAM, a 1 Gbit DRAM or a system LSI with a 0.15 μm through 0.13 μm rule, a pattern formation method using, as exposing light, ArF excimer laser lasing at a shorter wavelength (of a 193 nm band) than the KrF excimer laser is now under development. 
     The chemically amplified resist material including a polyhydroxystyrene derivative as a principal constituent has high absorbance against light of a wavelength of a 193 nm band because of an aromatic ring included therein. Therefore, exposing light of a wavelength of a 193 nm band cannot uniformly reach the bottom of a resist film, and hence, a pattern cannot be formed in a good shape. Accordingly, the chemically amplified resist material including a polyhydroxystyrene derivative as a principal constituent cannot be used when the ArF excimer laser is used as the exposing light. 
     Therefore, a chemically amplified resist material including, as a principal constituent, a polyacrylic acid derivative or a polycycloolefin derivative having no aromatic ring is used when the ArF excimer laser is used as the exposing light. 
     On the other hand, as exposing light for a pattern formation method capable of coping with high resolution, an electron beam (EB) and the like are being examined. 
     When the EB is used as the exposing light, however, the throughput is disadvantageously low, and hence, the EB is not suitable to mass production. Thus, the EB is not preferred as the exposing light. 
     Accordingly, in order to form a resist pattern finer than 0.10 μm, it is necessary to use exposing light of a wavelength shorter than that of the ArF excimer laser, such as Xe 2  laser (of a wavelength of a 172 nm band), F 2  laser (of a wavelength of a 157 nm band), Kr 2  laser (of a wavelength of a 146 nm band), ArKr laser (of a wavelength of 134 nm band), Ar 2  laser (of a wavelength of a 126 nm band), soft X-rays (of a wavelength of a 13, 11 or 5 nm band) and hard X-rays (of a wavelength not longer than a 1 nm band). In other words, a resist pattern is required to be formed by using exposing light of a wavelength not longer than a 180 nm band. 
     Therefore, the present inventors have formed resist patterns by conducting pattern exposure using F 2  laser (of a wavelength of a 157 nm band) on resist films formed from conventionally known chemically amplified resist materials respectively including a polyhydroxystyrene derivative represented by Chemical Formula A, a polyacrylic acid derivative represented by Chemical Formula B and a polycycloolefin derivative represented by Chemical Formula C.                           
     Now, a method for forming a resist pattern by using any of the aforementioned conventional chemically amplified resist materials and problems arising in the conventional method will be described with reference to FIGS. 2A through 2D. 
     First, as shown in FIG. 2A, the chemically amplified resist material is applied on a semiconductor substrate  1  by spin coating and the resultant is heated, so as to form a resist film  2  with a thickness of 0.3 μm. Thereafter, as shown in FIG. 2B, the resist film  2  is irradiated with a F 2  laser beam  4  through a mask  3  for pattern exposure. Thus, an acid is generated from the acid generator in an exposed portion  2   a  of the resist film  2  while no acid is generated in an unexposed portion  2   b  of the resist film  2 . 
     Next, as shown in FIG. 2C, the semiconductor substrate  1  is heated with a hot plate  5  at, for example 100° C. for 60 seconds. 
     Then, the resist film  2  is developed with an alkaline developer, thereby forming a resist pattern  6  as shown in FIG.  2 D. 
     However, as shown in FIG. 2D, the resist pattern  6  cannot be formed in a good pattern shape, and there remains much scum on the semiconductor substrate  1 . Such problems occur not only in using the F 2  laser beam as the exposing light but also in using any of the other light of a wavelength not longer than a 180 nm band. 
     Accordingly, a resist pattern cannot be practically formed by irradiating a resist film formed from any of the aforementioned chemically amplified resist materials with light of a wavelength not longer than a 180 nm band. 
     SUMMARY OF THE INVENTION 
     In consideration of the aforementioned conventional problems, an object of the invention is forming a resist pattern in a good pattern shape by using exposing light of a wavelength not longer than a 180 nm band with minimally producing scum. 
     The present inventors have studied the cause of the conventional problems occurring in using the conventional chemically amplified resist materials and have found the following: 
     First, the chemically amplified resist materials have high absorbance against light of a wavelength not longer than a 180 nm band. For example, a resist film with a thickness of 100 nm formed from the chemically amplified resist material including a polyhydroxystyrene derivative has transmittance of 20% at most against a F 2  laser beam (of a wavelength of a 157 nm band). 
     Therefore, various examination has been made on means for improving the transmittance of a chemically amplified resist material against light of a wavelength not longer than a 180 nm band. As a result, it has been found that a unit represented by Chemical Formula 1 below and a unit represented by Chemical Formula 2 below can improve the transmittance against light of a wavelength not longer than a 180 nm band. 
     The present invention was devised on the basis of the aforementioned finding, and specifically provides pattern formation materials and methods described below. 
     The first pattern formation material of this invention comprises a base polymer including a first unit represented by Chemical Formula 1 and a second unit represented by Chemical Formula 2; and an acid generator:                           
     wherein R 1  and R 2  are the same or different and selected from the group consisting of a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group and an alkyl group including a fluorine atom; R 3  is a protecting group released by an acid; m is an integer of 0 through 5; and a and b satisfy 0&lt;a&lt;1,0&lt;b&lt;1 and 0&lt;a+b≦1. 
     Since the base polymer of the first pattern formation material includes the first and second units respectively represented by Chemical Formulas 1 and 2, the transmittance of a resist film against light of a wavelength not longer than a 180 nm band can be improved. Also, since R 3  is released from the second unit owing to the function of an acid so as to generate hexafluoroisopropyl alcohol, the solubility in a developer of an exposed portion of the resist film can be improved. Therefore, the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be improved, and the wettability of the resist film is improved so as to improve adhesion between the resist film and a substrate. Furthermore, since the second unit has a benzene ring, resistance against dry etching can be improved. 
     In the first pattern formation material, the base polymer can be prepared through radical polymerization of the first unit and the second unit. 
     Alternatively, in the first pattern formation material, the base polymer can be prepared by obtaining a polymer through radical polymerization of the first unit and a precursor obtained before substituting R 3  for the second unit and allowing R 3  to bond to the precursor included in the polymer. 
     The second pattern formation material of this invention comprises a base polymer including a first unit represented by Chemical Formula 1, a second unit represented by Chemical Formula 2 and a third unit represented by Chemical Formula 3; and an acid generator:                           
     wherein R 1 , R 2  and R 4  are the same or different and selected from the group consisting of a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group and an alkyl group including a fluorine atom; R 3  is a protecting group released by an acid; m and n are integers of 0 through 5; and a, b and c satisfy 0&lt;a&lt;1,0&lt;b&lt;1,0&lt;c&lt;1 and 0&lt;a+b+c≦1. 
     Since the base polymer of the second pattern formation material includes the first through third units respectively represented by Chemical Formulas 1 through 3, the transmittance of a resist film against light of a wavelength not longer than a 180 nm band can be largely improved. Also, R 3  is released from the second unit owing to the function of an acid so as to generate hexafluoroisopropyl alcohol and the third unit has hexafluoroisopropyl alcohol. Therefore, the solubility in a developer of an exposed portion of the resist film can be improved so as to largely improve the contrast in solubility between the exposed portion and an unexposed portion of the resist film, and the wettability of the resist film can be improved so as to largely improve the adhesion between the resist film and a substrate. Furthermore, since the second unit and the third unit respectively have benzene rings, the resistance against dry etching can be largely improved. 
     In the second pattern formation material, the base polymer can be prepared through radical polymerization of the first unit, the second unit and the third unit. 
     Alternatively, in the second pattern formation material, the base polymer can be prepared by obtaining a polymer through radical polymerization of the first unit and the third unit and substituting R 3  for some of H of OH groups of the third unit included in the polymer. 
     The third pattern formation material of this invention comprises a base polymer including a first unit represented by Chemical Formula 1 and a second unit represented by Chemical Formula 4; and an acid generator:                           
     wherein R 1  is a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group or an alkyl group including a fluorine atom; R 5  is a protecting group released by an acid; p is an integer of 0 through 5; and a and d satisfy 0&lt;a&lt;1,0&lt;d&lt;1 and 0&lt;a+d≦1. 
     Since the base polymer of the third pattern formation material includes the first and second units, the transmittance of a resist film against light of a wavelength not longer than a 180 nm band can be improved. In particular, since the second unit has a norbornene ring, the transmittance of the resist film against light of a wavelength not longer than a 180 nm band can be further improved than that attained by the first pattern formation material. Also, since R 5  is released from the second unit owing to the function of an acid so as to generate hexafluoroisopropyl alcohol, the solubility in a developer of an exposed portion of the resist film can be improved. Therefore, the contrast in the solubility between the exposed portion and an unexposed portion of the resist film can be improved, and the wettability of the resist film can be improved so as to improve the adhesion between the resist film and a substrate. Furthermore, since the second unit has a norbornene ring, the resistance against dry etching can be improved. 
     In the third pattern formation material, the base polymer can be prepared through radical polymerization of the first unit and the second unit. 
     Alternatively, in the third pattern formation material, the base polymer can be prepared by obtaining a polymer through radical polymerization of the first unit and a precursor obtained before substituting R 5  for the second unit and allowing R 5  to bond to the precursor included in the polymer. 
     The fourth pattern formation material of this invention comprises a base polymer including a first unit represented by Chemical Formula 1, a second unit represented by Chemical Formula 4 and a third unit represented by Chemical Formula 5; and an acid generator:                           
     wherein R 1  is a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group or an alkyl group including a fluorine atom; R 5  is a protecting group released by an acid; p and q are integers of 0 through 5; and a, d and e satisfy 0&lt;a&lt;1,0&lt;d&lt;1,0&lt;e&lt;1 and 0&lt;a+d+e≦1. 
     Since the base polymer of the fourth pattern formation material includes the first through third units, the transmittance of a resist film against light of a wavelength not longer than a 180 nm band can be largely improved. In particular, since the second unit and the third unit respectively have norbornene rings, the transmittance of the resist film against light of a wavelength not longer than a 180 nm band can be further improved than that attained by the second pattern formation material. Also, R 5  is released from the second unit owing to the function of an acid so as to generate hexafluoroisopropyl alcohol and the third unit has hexafluoroisopropyl alcohol. Therefore, the solubility in a developer of an exposed portion of the resist film can be improved so as to largely improve the contrast in the solubility between the exposed portion and an unexposed portion of the resist film, and the wettability of the resist film can be improved so as to largely improve the adhesion between the resist film and a substrate. Furthermore, since the second unit and the third unit respectively have norbornene rings, the resistance against dry etching can be largely improved. 
     The first pattern formation method of this invention comprises the steps of forming a resist film by applying the first pattern formation material on a substrate; irradiating the resist film with exposing light of a wavelength not longer than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure. 
     Since the first pattern formation material is used in the first pattern formation method, the transmittance of the resist film against light of a wavelength not longer than a 180 nm band can be improved, the contrast in the solubility between an exposed portion and an unexposed portion of the resist film can be improved, the adhesion between the resist film and the substrate can be improved, and the resistance against dry etching can be improved. 
     The second pattern formation method of this invention comprises the steps of forming a resist film by applying the second pattern formation material on a substrate; irradiating the resist film with exposing light of a wavelength not longer than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure. 
     Since the second pattern formation material is used in the second pattern formation method, the transmittance of the resist film against light of a wavelength not longer than a 180 nm band can be largely improved, the contrast in the solubility between an exposed portion and an unexposed portion of the resist film can be largely improved, the adhesion between the resist film and the substrate can be largely improved, and the resistance against dry etching can be largely improved. 
     The third pattern formation method of this invention comprises the steps of forming a resist film by applying the third pattern formation material on a substrate; irradiating the resist film with exposing light of a wavelength not longer than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure. 
     Since the third pattern formation material is used in the third pattern formation method, the transmittance of the resist film against light of a wavelength not longer than a 180 nm band can be further improved, the contrast in the solubility between an exposed portion and an unexposed portion of the resist film can be improved, the adhesion between the resist film and the substrate can be improved, and the resistance against dry etching can be improved. 
     The fourth pattern formation method of this invention comprises the steps of forming a resist film by applying the fourth pattern formation material on a substrate; irradiating the resist film with exposing light of a wavelength not longer than a 180 nm band for pattern exposure; and forming a resist pattern by developing the resist film after the pattern exposure. 
     Since the fourth pattern formation material is used in the fourth pattern formation method, the transmittance of the resist film against light of a wavelength not longer than a 180 nm band can be further largely improved, the contrast in the solubility between an exposed portion and an unexposed portion of the resist film can be largely improved, the adhesion between the resist film and the substrate can be largely improved, and the resistance against dry etching can be largely improved. 
     In any of the first through fourth pattern formation methods, the exposing light may be light of a wavelength of a 110 through 180 nm band, such as a Xe 2  laser beam, a F 2  laser beam, a Kr 2  laser beam, an ArKr laser beam or an Ar 2  laser beam, a soft X-ray beam of a wavelength of a 1 through 30 nm band, or a hard X-ray beam of a wavelength not longer than a 1 nm band. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A,  1 B,  1 C and  1 D are cross-sectional views for showing procedures in a pattern formation method according to any of Embodiments 1 through 4 of the invention; and 
     FIGS. 2A,  2 B,  2 C and  2 D are cross-sectional views for showing procedures in a conventional pattern formation method. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiment 1 
     A pattern formation material and a pattern formation method according to Embodiment 1 of the invention will now be described. 
     In this embodiment, the first pattern formation material and the first pattern formation method described above are embodied, and the specific composition of a resist material of this embodiment is as follows: 
     Base polymer: a polymer represented by Chemical Formula 6 below 
     Acid generator: triphenylsulfonium triflate (5 wt % based on the base polymer) 
     Solvent: propylene glycol monomethyl ether acetate                           
     Chemical Formula 6 represents a specific example of a base polymer including the above-described first and second units respectively represented by Chemical Formulas 1 and 2. 
     In the first unit and the second unit, R 1  and R 2  may be the same or different and selected from the group consisting of a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group and an alkyl group including a fluorine atom. 
     In the second unit, R 3  may be any of protecting groups represented by Chemical Formula 7 below:                           
     Although m is 0 in the second unit, m may be an integer of 1 through 5 instead. 
     Now, a first synthesis method for the base polymer of the first pattern formation material will be described with reference to Chemical Formula 8 below.                           
     As represented by Chemical Formula 8, the base polymer of the first pattern formation material is prepared through radical polymerization of the first unit represented by Chemical Formula 1 and the second unit represented by Chemical Formula 2. In this case, the first unit and the second unit can be easily radical polymerized. 
     Next, a second synthesis method for the base polymer of the first pattern formation material will be described with reference to Chemical Formula 9 below.                           
     After placing AIBN (α,α-azobis(isobutyronitrile)) serving as a catalyst in a polymerization tube, 0.22 g (2 mmol) of vinyl sulfonyl fluoride (SO 2 F) (corresponding to the first unit) and 0.54 g (2 mmol) of 4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropyl)styrene (HFISt) (corresponding to a precursor obtained before substituting R 3  for the second unit), both of which are separately synthesized in syringes, and toluene are introduced into the polymerization tube. 
     Then, the resultant is sufficiently freeze deaerated, and the polymerization tube is sealed and heated, so as to cause radical polymerization of the first unit and the precursor. In this case, the first unit and the precursor can be easily radical polymerized. 
     After completing the polymerization reaction, the polymerization tube is unsealed and the toluene is removed with an evaporator. Next, the thus obtained polymer is dissolved in acetone, and the resultant is precipitated in hexane again. The thus obtained solid is heated under reduced pressure and sufficiently dried, and the resultant solid is dissolved in acetone again and precipitated in distilled water. The thus obtained white solid is dried, so as to give a SO 2 F-HFISt polymer. 
     Now, the pattern formation method of Embodiment 1 will be described with reference to FIGS. 1A through 1D. 
     First, as shown in FIG. 1A, the resist material having the above-described composition is applied on a semiconductor substrate  10  by spin coating, thereby forming a resist film  11  with a thickness of 0.2 μm. At this point, since the base polymer is alkali-refractory, the resist film  11  is alkali-refractory. 
     Next, as shown in FIG. 1B, the resist film  11  is subjected to pattern exposure by irradiating through a mask  12  with F 2  excimer laser  13  (of a wavelength of a 157 nm band). Thus, an acid is generated from the acid generator in an exposed portion  11   a  of the resist film  11  while no acid is generated in an unexposed portion  11   b  of the resist film  11 . 
     Then, as shown in FIG. 1C, the semiconductor substrate  10  together with the resist film  11  is heated with a hot plate  14 . Thus, the base polymer is heated in the presence of the acid in the exposed portion  11   a  of the resist film  11 , so as to release a protecting group from the unit of Chemical Formula 2. As a result, the base polymer becomes alkali-soluble. 
     Subsequently, the resist film  11  is developed with an alkaline developer such as a tetramethylammonium hydroxide aqueous solution. Thus, the exposed portion  11   a  of the resist film  11  is dissolved in the developer, so that a resist pattern  15  can be formed from the unexposed portion  11   b  of the resist film  11  as shown in FIG.  1 D. 
     Embodiment 2 
     A pattern formation material and a pattern formation method according to Embodiment 2 of the invention will now be described. Embodiment 2 is different from Embodiment 1 in the resist material alone, and hence, the resist material alone will be herein described. 
     In this embodiment, the second pattern formation material and the second pattern formation method described above are embodied, and the specific composition of the resist material is as follows: 
     Base polymer: a polymer represented by Chemical Formula 10 below 
     Acid generator: triphenylsulfonium triflate (5 wt % based on the base polymer) 
     Solvent: propylene glycol monomethyl ether acetate                           
     Chemical Formula 10 represents a specific example of a base polymer including the above-described first through third units respectively represented by Chemical Formulas 1 through 3. 
     In the first, second and third units, R 1 , R 2  and R 4  may be the same or different and selected from the group consisting of a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group and an alkyl group including a fluorine atom. 
     In the second unit, R 3  may be, for example, any of the protecting groups represented by Chemical Formula 7. 
     Although m is 0 in the second unit, m may be an integer of 1 through 5 instead. 
     Also, although n is 0 in the third unit, n may be an integer of 1 through 5 instead. 
     Now, a first synthesis method for the base polymer of the second pattern formation material will be described with reference to Chemical Formula 11 below.                           
     As represented by Chemical Formula 11, the base polymer of the second pattern formation material is obtained through the radical polymerization of the first unit represented by Chemical Formula 1, the second unit represented by Chemical Formula 2 and the third unit represented by Chemical Formula 3. In this case, the first unit, the second unit and the third unit can be easily radical polymerized. 
     Next, a second synthesis method for the base polymer of the second pattern formation material will be described with reference to Chemical Formula 12 below.                           
     As represented by Chemical Formula 12, a copolymer is obtained through the radical polymerization of the first unit and the third unit, and R 3  is substituted for some of H of OH groups of the third unit included in the copolymer. In this case, the first unit and the third can be easily radical polymerized. 
     Embodiment 3 
     A pattern formation material and a pattern formation method according to Embodiment 3 of the invention will now be described. Embodiment 3 is different from Embodiment 1 in the resist material alone, and hence, the resist material alone will be herein described. 
     In this embodiment, the third pattern formation material and the third pattern formation method described above are embodied, and the specific composition of the resist material is as follows: 
     Base polymer: a polymer represented by Chemical Formula 13 below 
     Acid generator: triphenylsulfonium triflate (5 wt % based on the base polymer) 
     Solvent: propylene glycol monomethyl ether acetate                           
     Chemical Formula 13 represents a specific example of a base polymer including the above-described first and second units respectively represented by Chemical Formulas 1 and 4. 
     In the first unit, R 1  is a hydrogen atom, and may be a chlorine atom, a fluorine atom, an alkyl group or an alkyl group including a fluorine group instead. 
     In the second unit, R 5  may be, for example, any of the protecting groups represented by Chemical Formula 7. 
     Also, although p is 1 in the second unit, p may be 0 or an integer of 2 through 5 instead. 
     Now, a first synthesis method for the base polymer of the third pattern formation material will be described with reference to Chemical Formula 14 below.                           
     As represented by Chemical Formula 14, the base polymer of the third pattern formation material is obtained through the radical polymerization of the first unit represented by Chemical Formula 1 and the second unit represented by Chemical Formula 4. In this case, the first unit and the second unit can be easily radical polymerized. 
     Next, a second synthesis method for the base polymer of the third pattern formation material will be described with reference to Chemical Formula 15 below.                           
     As represented by Chemical Formula 15, a copolymer is obtained through the radical polymerization of the first unit represented by Chemical Formula 1 and a precursor obtained before substituting R 5  for the second unit represented by Chemical Formula 4, and R 5  is allowed to bond to the precursor included in the copolymer. In this case, the first unit and the precursor can be easily radical polymerized. 
     Embodiment 4 
     A pattern formation material and a pattern formation method according to Embodiment 4 of the invention will now be described. Embodiment 4 is different from Embodiment 1 in the resist material alone, and hence, the resist material alone will be herein described. 
     In this embodiment, the fourth pattern formation material and the fourth pattern formation method described above are embodied, and the specific composition of the resist material is as follows: 
     Base polymer: a polymer represented by Chemical Formula 16 below 
     Acid generator: triphenylsulfonium triflate (5 wt % based on the base polymer) 
     Solvent: propylene glycol monomethyl ether acetate                           
     Chemical Formula 16 represents a specific example of a base polymer including the above-described first through third units respectively represented by Chemical Formulas 1, 4 and 5. 
     In the first unit, R 1  is a hydrogen atom, and may be a chlorine atom, a fluorine atom, an alkyl group or an alkyl group including a fluorine atom instead. 
     In the second unit, R 5  may be, for example, any of the protecting groups represented by Chemical Formula 7. 
     Also, although p is 1 in the second unit, p may be 0 or an integer of 2 through 5 instead. 
     Although q is 1 in the third unit, q may be 0 or an integer of 2 through 5 instead. 
     A first synthesis method for the base polymer of the fourth pattern formation material will be described with reference to Chemical Formula 17 below.                           
     As represented by Chemical Formula 17, the base polymer of the fourth pattern formation material is obtained through the radical polymerization of the first unit represented by Chemical Formula 1, the second unit represented by Chemical Formula 4 and the third unit represented by Chemical Formula 5. In this case, the first unit, the second unit and the third unit can be easily radical polymerized. 
     Next, a second synthesis method for the base polymer of the fourth pattern formation material will be described with reference to Chemical Formula 18 below.                           
     As represented by Chemical Formula 18, a copolymer is obtained through the radical polymerization of the first unit represented by Chemical Formula 1 and the third unit represented by Chemical Formula 5, and R 5  is substituted for some of H of OH groups of the third unit included in the copolymer. In this case, the first unit and the third unit can be easily radical polymerized. 
     Although the F 2  laser beam is used as the exposing light in Embodiments 1 through 4, the exposing light may be light of a wavelength of a 110 through 180 nm band, such as a Xe 2  laser beam, a Kr 2  laser beam, an ArKr laser beam and an Ar 2  laser beam, a soft X-ray beam of a wavelength of a 1 through 30 nm band or a hard X-ray beam of a wavelength not longer than a 1 nm band.