Method for forming resist pattern

Abstract

To provide a formation method of a resist pattern, with which pattern clarity can be ensured and an amount of a development residual can be reduced.SOLUTION: A formation method of a resist pattern includes: a step to coat a positive type resist composition comprising a copolymer having a monomer unit (I) and a monomer unit (II) on a workpiece; a step to form a resist film by drying at a temperature of 120-250°C; a step to expose the resist film; a step to conduct a post-exposure treatment consisting at least one of heating at 90-150°C and vacuum ultraviolet irradiation; and a step to develop the resist film.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for forming a resist pattern. [Background technology]

[0002] Conventionally, in the field of semiconductor manufacturing and the like, copolymers in which the main chain is cleaved and the solubility in a developer is increased by irradiation with ionizing radiation such as electron beams or short-wavelength light such as ultraviolet light (including extreme ultraviolet (EUV)) (hereinafter, ionizing radiation and short-wavelength light may be collectively referred to as "ionizing radiation, etc.") have been used as main-chain scission type positive resists.

[0003] Specifically, for example, Patent Document 1 discloses a positive resist composed of a copolymer containing α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and α-methylstyrene units as a main chain cleavage type positive resist excellent in sensitivity and heat resistance to ionizing radiation, etc. A positive resist composition containing such a copolymer and a solvent is dried to form a resist film on a workpiece, the resist film obtained is exposed, and then the exposed resist film is developed, whereby a resist pattern can be formed on the workpiece. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-154754 A Summary of the Invention [Problem to be solved by the invention]

[0005] Here, in the case of a main chain scission type positive resist, it is required that the obtained resist pattern is clear, that is, the boundary between the part where the resist film remains (residual film) and the part where it has dissolved is clear. Specifically, from the viewpoint of enabling the formation of a resist pattern with higher clarity, the resist is required to have the property that it does not dissolve in the developer unless the irradiation amount reaches a specific amount, and at the point where the irradiation amount reaches a specific amount, the main chain is quickly scissed and it dissolves in the developer, that is, to increase the γ value that represents the magnitude of the slope of the sensitivity curve that shows the relationship between the common logarithm of the irradiation amount of ionizing radiation, etc., and the remaining film thickness of the resist after development. Furthermore, when forming a resist pattern, it is necessary to suppress the generation of residues (hereinafter referred to as "resist residues") that are unintentionally left in space portions of the resist pattern.

[0006] Therefore, an object of the present invention is to provide a method of forming a resist pattern that is capable of reducing the amount of resist residue while ensuring the clarity of the resist pattern. [Means for solving the problem]

[0007] The present inventors have conducted extensive research in order to achieve the above object, and have discovered that when forming a resist pattern from a positive resist composition containing a copolymer formed using specific monomers, by setting the drying temperature when drying the positive resist composition to obtain a resist film within a specific range, and in addition, by heating the exposed resist film within a specific temperature range and / or irradiating it with vacuum ultraviolet light, the amount of resist residue can be reduced while ensuring the clarity required for the resist pattern, and have completed the present invention.

[0008] That is, an object of the present invention is to solve the above-mentioned problems in an advantageous manner, and the method for forming a resist pattern of the present invention comprises reacting a compound represented by the following formula (I): [ka] [In formula (I), X is a halogen atom, a cyano group, an alkylsulfonyl group, an alkoxy group, a nitro group, an acyl group, an alkyl ester group, or a halogenated alkyl group, L is a single bond or a divalent linking group, and Ar is an aromatic ring group which may have a substituent.] and a monomer unit (A) represented by the following formula (II): [ka] [In formula (II), R 1 is an alkyl group, R 2 is an alkyl group, a halogen atom, a halogenated alkyl group, a hydroxyl group, a carboxyl group, or a halogenated carboxyl group, p is an integer of 0 to 5, R 2 When a plurality of units are present, they may be the same or different. The resist composition includes a step of applying a positive resist composition containing a copolymer having a monomer unit (B) represented by the formula (A) and a solvent onto a workpiece, a step of drying the positive resist composition applied onto the workpiece at a temperature of 120° C. to 250° C. to form a resist film, a step of exposing the resist film, a step of performing a post-exposure treatment on the resist film after the exposure, which is at least one of heating at a temperature of 90° C. to 150° C. and irradiating with vacuum ultraviolet light, and a step of developing the resist film after the post-exposure treatment. In this way, by setting the drying temperature in forming a resist film using the positive resist composition containing the above-mentioned specific copolymer and solvent within the above-mentioned range and performing at least one of the above-mentioned post-exposure treatments on the exposed resist film, a resist pattern with ensured clarity and a small amount of resist residue can be obtained. In the present invention, the phrase "optionally having a substituent" means "unsubstituted or having a substituent". In addition, in the present invention, the "temperature" during drying and heating (hereinafter collectively referred to as "heating, etc.") means the temperature of the heat source when the target is heated, etc. by contacting it with a heat source (hot plate, etc.), and means the temperature of the medium (e.g., atmospheric temperature) when the target is heated, etc. from the heat source via a medium (air, etc.).

[0009] Here, in the method for forming a resist pattern of the present invention, the development is preferably carried out under conditions in which the residual film ratio at an exposure dose of 0.60 Eth exceeds 0.850. By carrying out development under conditions in which the residual film ratio at an exposure dose of 0.60 Eth exceeds 0.850, the clarity of the obtained resist pattern can be sufficiently improved. In the method for forming a resist pattern of the present invention, the development is preferably carried out under conditions in which the residual film ratio at an exposure dose of 0.80Eth is 0.600 or more. By carrying out the development under conditions in which the residual film ratio at an exposure dose of 0.80Eth is 0.600 or more, the clarity of the obtained resist pattern can be sufficiently improved.

[0010] In the present invention, "Eth" is an index representing the sensitivity of a resist, and is a guideline for the total dose of ionizing radiation, etc., which can reduce the residual film ratio of a resist irradiated with ionizing radiation, etc. and dissolved in a developer to approximately 0. Furthermore, "the residual film ratio at an exposure dose of 0.60Eth" means the exposure dose of Eth multiplied by 0.60, i.e., the residual film ratio of the resist film at an exposure dose of 60% of Eth (0≦remaining film ratio≦1.00), and "the residual film ratio at an exposure dose of 0.80Eth" means the exposure dose of Eth multiplied by 0.80, i.e., the residual film ratio of the resist film at an exposure dose of 80% of Eth (0≦remaining film ratio≦1.00). A residual film ratio of more than 0.850 at an exposure dose of 0.6Eth and / or a residual film ratio of 0.600 or more at an exposure dose of 0.80Eth means that dissolution of the resist at an exposure dose of 60% and / or 80% of Eth is suppressed to a very high level. Therefore, if development is performed under conditions that satisfy the above residual film ratio, the γ value can be sufficiently increased, and the clarity of the obtained resist pattern can be sufficiently improved. In the present invention, "Eth", "film remaining ratio when the irradiation amount is 0.60Eth" and "film remaining ratio when the irradiation amount is 0.80Eth" can all be calculated using the method described in the Examples. Effect of the Invention

[0011] According to the method of forming a resist pattern of the present invention, the amount of resist residue can be reduced while ensuring the clarity of the resulting resist pattern. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described in detail. The method for forming a resist pattern of the present invention is a method for forming a resist pattern that uses a main chain scission type positive resist in which the main chain is scissed and the molecular weight is reduced by irradiation with ionizing radiation such as an electron beam or short wavelength light such as ultraviolet light.

[0013] Furthermore, a resist pattern formed by the method for forming a resist pattern of the present invention can be used in an etching method in which a workpiece is etched using the resist pattern as a mask to form a pattern on the workpiece. Such a resist pattern forming method and etching method can be suitably used, for example, when producing a printed circuit board such as a build-up board.

[0014] (Method of forming a resist pattern) The resist pattern forming method of the present invention includes at least a step of applying a positive resist composition containing a copolymer onto a workpiece (application step), a step of drying the positive resist composition on the workpiece to form a resist film (resist film forming step), a step of exposing the resist film (exposure step), a step of performing post-exposure treatment on the exposed resist film (post-exposure treatment step), and a step of developing the resist film after post-exposure treatment (development step). The resist pattern forming method of the present invention may include steps other than the above-mentioned coating step, resist film forming step, exposure step, post-exposure treatment step, and development step. Specifically, the resist pattern forming method may include a step of forming an underlayer film on a substrate, which is a workpiece, before the coating step (underlayer film forming step). The resist pattern forming method may also include a step of removing a developer after the development step (developer removing step). Furthermore, the resist pattern forming method may include a step of irradiating the resist film with vacuum ultraviolet light (pre-irradiation step) between the resist film forming step and the exposure step. In addition, the resist pattern forming method may include a step of irradiating the developed film with vacuum ultraviolet light after the development step, between the development step and the developer removing step, and / or after the developer removing step (post-irradiation step).

[0015] Here, the resist pattern forming method of the present invention is characterized in that a copolymer having the above-mentioned monomer unit (A) and monomer unit (B) is used as the copolymer contained in the positive resist composition, the positive resist composition is dried at a prescribed temperature to form a resist film in the resist film formation step, and the exposed resist film is heated at a prescribed temperature and / or irradiated with vacuum ultraviolet light in the post-exposure treatment step.

[0016] The main chain of the copolymer described above is easily cleaved and the molecular weight is reduced when the copolymer is irradiated with ionizing radiation or the like (for example, an electron beam, a KrF laser, an ArF laser, an EUV laser, etc.). In the method for forming a resist pattern of the present invention, the resist film formation step and the post-exposure treatment step described above are performed, so that a resist pattern with ensured clarity and with a small amount of resist residue can be obtained. Furthermore, by using the method for forming a resist pattern of the present invention, it is possible to suppress collapse of the resist pattern (pattern collapse) that may occur during the series of steps of forming the resist pattern.

[0017] <Positive resist composition> The positive resist composition used in the method of forming a resist pattern of the present invention contains a specific copolymer, which will be described in detail below as a positive resist, and further contains a solvent. Furthermore, the positive resist composition optionally further contains known additives that can be blended into resist compositions. Furthermore, the positive resist composition may contain a polymer other than the copolymer specified as a positive resist, but typically contains only the specified copolymer as a positive resist.

[0018] <<Copolymer>> The copolymer contained in the positive resist composition has a specific monomer unit (A) and a specific monomer unit (B). The copolymer may contain any monomer unit other than the monomer unit (A) and the monomer unit (B). However, the proportion of the monomer unit (A) and the monomer unit (B) in all the monomer units constituting the copolymer is preferably 90 mol % or more in total, and more preferably 100 mol % (i.e., the copolymer contains only the monomer unit (A) and the monomer unit (B)).

[0019] [Monomer unit (A)] Here, the monomer unit (A) is represented by the following formula (I): [ka] [In formula (I), X is a halogen atom, a cyano group, an alkylsulfonyl group, an alkoxy group, a nitro group, an acyl group, an alkyl ester group, or a halogenated alkyl group, L is a single bond or a divalent linking group, and Ar is an aromatic ring group which may have a substituent.] and represented by the following formula (III): [ka] [In the formula (III), X, L and Ar are the same as those in the formula (I)].

[0020] Here, examples of halogen atoms that can constitute X in formula (I) and formula (III) include chlorine atoms, fluorine atoms, bromine atoms, iodine atoms, and astatine atoms. Examples of alkylsulfonyl groups that can constitute X in formula (I) and formula (III) include methylsulfonyl groups and ethylsulfonyl groups. Examples of alkoxy groups that can constitute X in formula (I) and formula (III) include methoxy groups, ethoxy groups, and propoxy groups. Examples of acyl groups that can constitute X in formula (I) and formula (III) include formyl groups, acetyl groups, and propionyl groups. Examples of alkyl ester groups that can constitute X in formula (I) and formula (III) include methyl ester groups and ethyl ester groups. Examples of halogenated alkyl groups that can constitute X in formula (I) and formula (III) include halogenated methyl groups having 1 to 3 halogen atoms. Among these, from the viewpoint of efficiently obtaining a copolymer useful as a main chain scission type positive resist, X is preferably a halogen atom, and more preferably a chlorine atom.

[0021] Furthermore, the divalent linking group that can constitute L in formula (I) and formula (III) is not particularly limited, and examples thereof include an alkylene group which may have a substituent, and an alkenylene group which may have a substituent.

[0022] The alkylene group of the alkylene group which may have a substituent is not particularly limited, and examples thereof include linear alkylene groups such as methylene, ethylene, propylene, n-butylene, and isobutylene, and cyclic alkylene groups such as 1,4-cyclohexylene. Among them, the alkylene group is preferably a linear alkylene group having 1 to 6 carbon atoms such as methylene, ethylene, propylene, n-butylene, and isobutylene, more preferably a linear alkylene group having 1 to 6 carbon atoms such as methylene, ethylene, propylene, and n-butylene, and even more preferably a linear alkylene group having 1 to 3 carbon atoms such as methylene, ethylene, and propylene. The alkenylene group of the alkenylene group which may have a substituent is not particularly limited, and examples thereof include chain alkenylene groups such as ethenylene group, 2-propenylene group, 2-butenylene group, and 3-butenylene group, and cyclic alkenylene groups such as cyclohexenylene group. Among them, the alkenylene group is preferably a straight-chain alkenylene group having 2 to 6 carbon atoms such as ethenylene group, 2-propenylene group, 2-butenylene group, and 3-butenylene group.

[0023] Among the above, from the viewpoint of sufficiently improving the sensitivity to ionizing radiation and the like, the divalent linking group is preferably an alkylene group which may have a substituent, more preferably a chain alkylene group having 1 to 6 carbon atoms which may have a substituent, still more preferably a linear alkylene group having 1 to 6 carbon atoms which may have a substituent, and particularly preferably a linear alkylene group having 1 to 3 carbon atoms which may have a substituent.

[0024] From the viewpoint of further improving the sensitivity to ionizing radiation, etc., the divalent linking group capable of constituting L in formula (I) and formula (III) preferably has one or more electron-withdrawing groups. In particular, when the divalent linking group is an alkylene group having an electron-withdrawing group as a substituent or an alkenylene group having an electron-withdrawing group as a substituent, it is preferred that the electron-withdrawing group is bonded to the carbon bonded to O adjacent to the carbonyl carbon in formula (I) and formula (III).

[0025] The electron-withdrawing group capable of sufficiently improving the sensitivity to ionizing radiation and the like is not particularly limited, and may be, for example, at least one selected from the group consisting of a fluorine atom, a fluoroalkyl group, a cyano group, and a nitro group. The fluoroalkyl group is not particularly limited, and may be, for example, a fluoroalkyl group having 1 to 5 carbon atoms. Among them, the fluoroalkyl group is preferably a perfluoroalkyl group having 1 to 5 carbon atoms, and more preferably a trifluoromethyl group.

[0026] From the viewpoint of sufficiently improving the sensitivity to ionizing radiation and the like, L in formula (I) and formula (III) is preferably a methylene group, a cyanomethylene group, a trifluoromethylmethylene group or a bis(trifluoromethyl)methylene group, and more preferably a bis(trifluoromethyl)methylene group.

[0027] Moreover, Ar in the formula (I) and the formula (III) includes an aromatic hydrocarbon ring group which may have a substituent and an aromatic heterocyclic group which may have a substituent.

[0028] The aromatic hydrocarbon ring group is not particularly limited, and examples thereof include a benzene ring group, a biphenyl ring group, a naphthalene ring group, an azulene ring group, an anthracene ring group, a phenanthrene ring group, a pyrene ring group, a chrysene ring group, a naphthacene ring group, a triphenylene ring group, an o-terphenyl ring group, an m-terphenyl ring group, a p-terphenyl ring group, an acenaphthene ring group, a coronene ring group, a fluorene ring group, a fluoranthrene ring group, a pentacene ring group, a perylene ring group, a pentaphene ring group, a picene ring group, and a pyranthrene ring group.

[0029] Furthermore, examples of the aromatic heterocyclic group include, but are not limited to, a furan ring group, a thiophene ring group, a pyridine ring group, a pyridazine ring group, a pyrimidine ring group, a pyrazine ring group, a triazine ring group, an oxadiazole ring group, a triazole ring group, an imidazole ring group, a pyrazole ring group, a thiazole ring group, an indole ring group, a benzimidazole ring group, a benzothiazole ring group, a benzoxazole ring group, a quinoxaline ring group, a quinazoline ring group, a phthalazine ring group, a benzofuran ring group, a dibenzofuran ring group, a benzothiophene ring group, a dibenzothiophene ring group, and a carbazole ring group.

[0030] Furthermore, the substituent that Ar may have is not particularly limited, and examples thereof include an alkyl group, a fluorine atom, and a fluoroalkyl group. Examples of the alkyl group as the substituent that Ar may have include a chain alkyl group having 1 to 6 carbon atoms, such as a methyl group, an ethyl group, a propyl group, an n-butyl group, and an isobutyl group. Examples of the fluoroalkyl group as the substituent that Ar may have include a fluoroalkyl group having 1 to 5 carbon atoms, such as a trifluoromethyl group, a trifluoroethyl group, and a pentafluoropropyl group.

[0031] Among these, from the viewpoint of sufficiently improving the sensitivity to ionizing radiation and the like, Ar in formula (I) and formula (III) is preferably an aromatic hydrocarbon ring group which may have a substituent, more preferably an unsubstituted aromatic hydrocarbon ring group, and even more preferably a benzene ring group (phenyl group).

[0032] From the viewpoint of sufficiently improving the sensitivity to ionizing radiation, etc., the monomer (a) represented by the above formula (III) capable of forming the monomer unit (A) represented by the above formula (I) is preferably α-chloroacrylate benzyl and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl, more preferably α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl. That is, the copolymer preferably has at least one of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl unit and α-chloroacrylate benzyl unit, more preferably α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl unit.

[0033] The proportion of the monomer unit (A) in the total monomer units constituting the copolymer is not particularly limited, and can be, for example, 30 mol% or more and 70 mol% or less. In particular, the proportion of the monomer unit (A) is preferably 50 mol% or more, more preferably more than 50 mol%, even more preferably 52 mol% or more, preferably 60 mol% or less, more preferably 55 mol% or less, and even more preferably 54 mol% or less. If the proportion of the monomer unit (A) is within the above range, the clarity of the resist pattern can be further improved.

[0034] [Monomer unit (B)] The monomer unit (B) has the following formula (II): [ka] [In formula (II), R 1 is an alkyl group, R 2 is an alkyl group, a halogen atom, a halogenated alkyl group, a hydroxyl group, a carboxyl group, or a halogenated carboxyl group (-C(=O)-X; X is a halogen atom), p is an integer of 0 to 5, R 2 When a plurality of are present, they may be the same or different. and represented by the following formula (IV): [ka] [In formula (IV), R 1 and R 2 and p is the same as in formula (II).

[0035] Here, R in formula (II) and formula (IV) 1 ~R 2 The alkyl group that can constitute R is not particularly limited, and examples thereof include unsubstituted alkyl groups having 1 to 5 carbon atoms. 1 ~R 2 The alkyl group which can constitute the above group is preferably a methyl group or an ethyl group.

[0036] In addition, R in formula (II) and formula (IV) 2 The halogen atom which can constitute the ring structure is not particularly limited, and examples thereof include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. Among these, the halogen atom is preferably a fluorine atom.

[0037] Furthermore, R in formula (II) and formula (IV) 2 The halogenated alkyl group that can constitute the above is not particularly limited, and examples thereof include fluoroalkyl groups having 1 to 5 carbon atoms. Among them, the halogenated alkyl group is preferably a perfluoroalkyl group having 1 to 5 carbon atoms, and more preferably a trifluoromethyl group.

[0038] In addition, R in formula (II) and formula (IV) 2 Examples of halogenated carboxyl groups that can constitute the above formula include, but are not limited to, a chlorocarboxyl group (-C(=O)-Cl), a fluorinated carboxyl group (-C(=O)-F), and a brominated carboxyl group (-C(=O)-Br).

[0039] From the viewpoint of easiness in preparation of the copolymer and improvement in severability of the main chain when irradiated with ionizing radiation or the like, R 1 is preferably an alkyl group having 1 to 5 carbon atoms, and more preferably a methyl group.

[0040] In addition, from the viewpoints of easiness in preparation of the copolymer and improving the severability of the main chain when irradiated with ionizing radiation or the like, p in formula (II) and formula (IV) is preferably 0 or 1.

[0041] Furthermore, when p in formula (II) and formula (IV) is any one of 1 to 5, R 2 is preferably an alkyl group having 1 to 5 carbon atoms, and more preferably a methyl group.

[0042] The monomer (b) represented by the above formula (IV) capable of forming the monomer unit (B) represented by the above formula (II) is not particularly limited, and examples thereof include α-methylstyrene and its derivatives such as the following (b-1) to (b-12). [ka]

[0043] From the viewpoints of ease of preparation of the copolymer and improving the severability of the main chain when irradiated with ionizing radiation, etc., the monomer unit (B) is preferably a structural unit derived from α-methylstyrene or 4-methyl-α-methylstyrene. That is, the copolymer preferably has an α-methylstyrene unit or a 4-methyl-α-methylstyrene unit.

[0044] The proportion of the monomer unit (B) in the total monomer units constituting the copolymer is not particularly limited, and can be, for example, 30 mol% or more and 70 mol% or less. In particular, the proportion of the monomer unit (B) is preferably 40 mol% or more, more preferably 45 mol% or more, even more preferably 46 mol% or more, preferably 50 mol% or less, more preferably less than 50 mol%, and even more preferably 48 mol% or less. If the proportion of the monomer unit (B) is within the above range, the clarity of the resist pattern can be further improved.

[0045] [Properties of copolymer] The copolymer preferably has a weight average molecular weight (Mw) of more than 100,000, more preferably at least 110,000, and even more preferably at least 150,000. If the weight average molecular weight of the copolymer is within the above range, the clarity of the resist pattern can be further improved. There are no particular upper limits for the weight average molecular weight of the copolymer, but from the standpoint of preventing filtration from becoming difficult when preparing a positive resist composition, it is preferably 500,000 or less.

[0046] The number average molecular weight (Mn) of the copolymer is preferably 70,000 or more, more preferably 110,000 or more, and is preferably 400,000 or less, and more preferably 300,000 or less. If the number average molecular weight of the copolymer is equal to or more than the lower limit, the clarity of the resist pattern can be further improved. If the number average molecular weight of the copolymer is equal to or less than the upper limit, the positive resist composition can be easily prepared.

[0047] The molecular weight distribution (Mw / Mn) of the copolymer is preferably 1.20 or more, more preferably 1.30 or more, even more preferably 1.40 or more, particularly preferably 1.50 or more, and is preferably 2.00 or less, more preferably 1.90 or less.

[0048] In the present invention, the "weight average molecular weight" and the "number average molecular weight" can be measured using gel permeation chromatography in terms of standard polystyrene, and the "molecular weight distribution" can be determined by calculating the ratio of the weight average molecular weight to the number average molecular weight (weight average molecular weight / number average molecular weight).

[0049] Furthermore, from the standpoint of efficiently forming a resist pattern with excellent clarity, it is preferable for the copolymer to satisfy at least one of the following (1) to (4), and it is more preferable for it to satisfy all of (1) to (4). (1) The proportion of components having a molecular weight of less than 10,000 is less than 1.5%, preferably 1.3% or less. (2) The proportion of components having a molecular weight of less than 50,000 is less than 30%, preferably 20% or less. (3) The proportion of components having a molecular weight of less than 100,000 is less than 70%, preferably 65% ​​or less, and more preferably 30% or less. (4) The proportion of components having a molecular weight of more than 200,000 is more than 8.0%, preferably 30% or more.

[0050] <<How to prepare copolymer>> The copolymer having the above-mentioned monomer unit (A) and monomer unit (B) can be prepared, for example, by polymerizing a monomer composition containing the monomer (a) and the monomer (b), recovering the obtained copolymer, and optionally purifying it. The composition, molecular weight distribution, weight average molecular weight, and number average molecular weight of the copolymer can be adjusted by changing the polymerization conditions (e.g., polymerization temperature, polymerization time, and type and amount of polymerization initiator) and purification conditions. Specifically, for example, the weight average molecular weight and number average molecular weight can be increased by lowering the polymerization temperature. Also, the weight average molecular weight and number average molecular weight can be increased by shortening the polymerization time. Furthermore, the molecular weight distribution can be narrowed by performing purification.

[0051] Here, as the monomer composition used for preparing the copolymer, a mixture of monomer components including monomer (a) and monomer (b), a solvent, an optionally added polymerization initiator, and an optionally added additive can be used. In addition, when polymerizing the monomer composition, emulsion polymerization can be suitably adopted as a polymerization method. As a solvent used in carrying out emulsion polymerization, water is suitable. In addition, as a surfactant used in emulsion polymerization, an anionic surfactant consisting of an alkali salt of a higher fatty acid, such as half-hardened beef tallow fatty acid potassium soap, can be suitably used. In addition, as a polymerization initiator used in emulsion polymerization, a water-soluble initiator such as potassium persulfate can be suitably used. In addition, in emulsion polymerization, a buffer such as sodium carbonate can be optionally used.

[0052] The polymer obtained by polymerizing the monomer composition may be used as a copolymer as it is, but is not particularly limited thereto. It can be recovered by adding a good solvent such as tetrahydrofuran to a solution containing the polymer, and then dropping the solution to which the good solvent has been added into a poor solvent such as methanol to coagulate the polymer.

[0053] The purification method used for purifying the obtained polymer is not particularly limited, and examples thereof include known purification methods such as reprecipitation and column chromatography. Among them, the reprecipitation method is preferably used as the purification method. The purification of the polymer may be repeated several times.

[0054] The purification of the polymer by the reprecipitation method is preferably carried out, for example, by dissolving the obtained polymer in a good solvent such as tetrahydrofuran, and then dropping the obtained solution into a mixed solvent of a good solvent such as tetrahydrofuran and a poor solvent such as methanol to precipitate a part of the polymer. In this way, if the solution of the polymer is dropped into a mixed solvent of a good solvent and a poor solvent to perform purification, the molecular weight distribution, weight average molecular weight and number average molecular weight of the obtained copolymer can be easily adjusted by changing the type and mixing ratio of the good solvent and the poor solvent. Specifically, for example, the molecular weight of the copolymer precipitated in the mixed solvent can be increased by increasing the ratio of the good solvent in the mixed solvent.

[0055] In addition, when purifying a polymer by the reprecipitation method, a polymer precipitated in a mixed solvent of a good solvent and a poor solvent may be used as the copolymer as long as it satisfies the desired properties, or a polymer not precipitated in the mixed solvent (i.e., a polymer dissolved in the mixed solvent) may be used. Here, the polymer not precipitated in the mixed solvent can be recovered from the mixed solvent by a known method such as concentration to dryness.

[0056] <<Solvent>> The solvent contained in the positive resist composition is not particularly limited as long as it is a solvent that can dissolve the above-mentioned copolymer, and it is possible to use known solvents such as those described in Japanese Patent No. 5938536. Among them, from the perspective of obtaining a positive resist composition with an appropriate viscosity and improving the coatability of the positive resist composition, it is preferable to use anisole, propylene glycol monomethyl ether acetate (PGMEA), cyclopentanone, cyclohexanone, or isoamyl acetate as the solvent.

[0057] <<Preparation of positive resist composition>> The positive resist composition can be prepared by mixing the above-mentioned copolymer, the solvent, and any known additives that can be used. In this case, the mixing method is not particularly limited, and the mixing may be performed by a known method. Alternatively, the positive resist composition may be prepared by mixing the components and then filtering the mixture.

[0058] Here, the method of filtering the mixture is not particularly limited, and for example, the mixture can be filtered using a filter. The filter is not particularly limited, and examples thereof include fluorocarbon, cellulose, nylon, polyester, and hydrocarbon filtration membranes. Among them, from the viewpoint of effectively preventing impurities such as metals from metal piping, etc., which may be used during the preparation of the copolymer, from being mixed into the positive resist composition, the material constituting the filter is preferably nylon, polyethylene, polypropylene, polytetrafluoroethylene, polyfluorocarbon such as Teflon (registered trademark), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polyimide, nylon, and a composite membrane of polyethylene and nylon. As the filter, for example, one disclosed in U.S. Pat. No. 6,103,122 may be used. In addition, the filter is commercially available as Zeta Plus (registered trademark) 40Q manufactured by CUNO Incorporated. Furthermore, the filter may contain a strong cationic or weak cationic ion exchange resin. Here, the average particle size of the ion exchange resin is not particularly limited, but is preferably 2 μm or more and 10 μm or less. Examples of cation exchange resins include sulfonated phenol-formaldehyde condensates, sulfonated phenol-benzaldehyde condensates, sulfonated styrene-divinylbenzene copolymers, sulfonated methacrylic acid-divinylbenzene copolymers, and other types of sulfonic or carboxylic acid group-containing polymers. + Counterion, NH4 + Counterion or alkali metal counterion, e.g. K + and Na +Counterions are provided. The cation exchange resin preferably has hydrogen counterions. Examples of such cation exchange resins include H + Sulfonated styrene-divinylbenzene copolymers with counterions include Microlite® PrCH from Purolite Corp. Such cation exchange resins are commercially available as AMBERLYST® from Rohm and Haas. Furthermore, the pore size of the filter is preferably from 0.001 μm to 1 μm. If the pore size of the filter is within the above range, it is possible to sufficiently prevent impurities such as metals from being mixed into the positive resist composition.

[0059] <Workpiece> The workpiece on which the resist pattern is formed may be a substrate that is processed using the resist pattern. The substrate may have an underlayer film formed through an underlayer film forming step described below.

[0060] <<Substrate>> The substrate is not particularly limited, and examples of the substrate that can be used include a substrate having an insulating layer and a copper foil provided on the insulating layer, which is used in the manufacture of printed circuit boards, and a mask blank having a light-shielding layer formed on a substrate.

[0061] Examples of the substrate material include inorganic materials such as metals (silicon, copper, chromium, iron, aluminum, etc.), glass, titanium oxide, silicon dioxide (SiO2), silica, and mica; nitrides such as SiN; oxynitrides such as SiON; and organic materials such as acrylic, polystyrene, cellulose, cellulose acetate, and phenolic resin. Among these, metals are preferred as the substrate material. By using, for example, a silicon substrate, a silicon dioxide substrate, or a copper substrate, preferably a silicon substrate or a silicon dioxide substrate, as the substrate, a cylindrical structure can be formed.

[0062] The size and shape of the substrate are not particularly limited. The surface of the substrate may be smooth, may have a curved surface or an uneven surface, or may be a thin plate-shaped substrate.

[0063] Furthermore, the surface of the substrate may be subjected to a surface treatment as necessary. For example, in the case of a substrate having a hydroxyl group on the surface layer of the substrate, the surface of the substrate can be treated with a silane coupling agent capable of reacting with the hydroxyl group. This changes the surface layer of the substrate from hydrophilic to hydrophobic, thereby improving the adhesion between the substrate and the underlayer film, or between the substrate and the resist film. In this case, the silane coupling agent is not particularly limited, but hexamethyldisilazane is preferred.

[0064] <Lower film formation process> In the underlayer film forming step optionally included in the resist pattern forming method of the present invention, an underlayer film can be provided on the above-mentioned substrate. By providing an underlayer film on the substrate, the surface of the substrate is made hydrophobic. This increases the affinity between the substrate and the resist film, thereby increasing the adhesion between the substrate and the resist film. The underlayer film may be an inorganic underlayer film or an organic underlayer film.

[0065] The inorganic underlayer film can be formed by applying an inorganic material onto a substrate and baking it, etc. Examples of the inorganic material include silicon-based materials.

[0066] The organic underlayer film can be formed by applying an organic material onto a substrate to form a coating film and drying it. The organic material is not limited to those having sensitivity to light or electron beams, and can be, for example, a resist material or a resin material commonly used in the semiconductor field and liquid crystal field. Among them, the organic material is preferably a material capable of forming an organic underlayer film capable of etching, particularly dry etching. With such an organic material, the pattern formed by processing the resist film can be used to etch the organic underlayer film, thereby transferring the pattern to the underlayer film to form a pattern of the underlayer film. Among them, the organic material is preferably a material capable of forming an organic underlayer film capable of etching, such as oxygen plasma etching. Examples of organic materials used for forming the organic underlayer film include AL412 from Brewer Science.

[0067] The organic material can be applied by a conventional method using spin coating or a spinner. The method for drying the coating film may be any method capable of volatilizing the solvent contained in the organic material, such as a baking method. The baking conditions are not particularly limited, but the baking temperature is preferably 80°C or more and 300°C or less, and more preferably 200°C or more and 300°C or less. The baking time is preferably 30 seconds or more, more preferably 60 seconds or more, preferably 500 seconds or less, more preferably 400 seconds or less, even more preferably 300 seconds or less, and particularly preferably 180 seconds or less. The thickness of the underlayer film after drying the coating film is not particularly limited, but is preferably 10 nm or more and 100 nm or less.

[0068] <Coating process> In the coating step, the positive resist composition is coated onto the workpiece such as the substrate (or onto the underlayer film if an underlayer film is formed). There are no particular limitations on the method for coating the positive resist composition, and any method commonly used for forming a resist film can be used.

[0069] <Resist film formation process> In the resist film forming step, the positive resist composition applied onto the workpiece in the above-mentioned application step is dried by heating (pre-baking) to form a resist film. The heating temperature (pre-baking temperature) in the resist film forming step must be 120° C. or higher and 250° C. or lower, and is preferably 140° C. or higher. If the pre-baking temperature is 120° C. or higher, the solvent can be sufficiently removed, and the clarity of the resist pattern can be sufficiently ensured. On the other hand, if the pre-baking temperature is 250° C. or lower, the molecular weight (weight average molecular weight) of the copolymer in the resist film is not excessively reduced by pre-baking, and the film loss of the obtained resist film can be suppressed.

[0070] The heating time (pre-baking time) in the resist film forming step is preferably 10 seconds or more, more preferably 20 seconds or more, and even more preferably 40 seconds or more, and is preferably 5 minutes or less, more preferably 3 minutes or less, and even more preferably 2 minutes or less. If the pre-baking time is within the above range, the clarity of the resist pattern can be further improved.

[0071] It is preferable that the weight average molecular weight (Mw) of the copolymer in the resist film formed in the resist film forming step is less different from the weight average molecular weight (Mw) of the copolymer in the positive resist composition before pre-baking. The weight average molecular weight (Mw) in the resist film is preferably more than 100,000, and the weight average molecular weight of the copolymer is more preferably 110,000 or more, even more preferably 150,000 or more, and is preferably 500,000 or less.

[0072] <Exposure process> In the exposure step, the resist film formed in the resist film forming step is irradiated with ionizing radiation or the like to draw a desired pattern. For irradiation with ionizing radiation, etc., known lithography devices such as electron beam lithography devices and laser lithography devices can be used. For example, for irradiation with EUV, known exposure devices such as EQ-10M (manufactured by ENERGETIQ) and NXE (manufactured by ASML) can be used.

[0073] <Post-exposure processing step> In the post-exposure treatment step, the resist film exposed in the exposure step is subjected to at least one post-exposure treatment of heating (post-exposure bake, PEB) and / or irradiation with vacuum ultraviolet light. It is believed that the post-exposure treatment promotes the homogenization of the molecular weight distribution in the exposed part of the resist film and the smoothing of the exposed part, thereby reducing the amount of resist residue, and that the post-exposure treatment improves the strength of the resist pattern, thereby suppressing pattern collapse. In the post-exposure treatment step, both heating and irradiation with vacuum ultraviolet light may be performed. For example, the resist film may be heated and then irradiated with vacuum ultraviolet light.

[0074] <<Heating (Post Exposure Bake)>> When performing post-exposure treatment by heating, the heating temperature in the post-exposure treatment step (post-exposure bake temperature) must be 90° C. or higher and 150° C. or lower, and is preferably 100° C. or higher. If the post-exposure bake temperature is 90° C. or higher, the amount of resist residue can be reduced and pattern collapse can be suppressed. On the other hand, if the post-exposure bake temperature is 150° C. or lower, the resist pattern can be prevented from becoming unclear or disappearing due to melting of the copolymer whose main chain has been scission.

[0075] In addition, when performing post-exposure treatment by heating, the heating time in the post-exposure treatment step (post-exposure bake time) is preferably 10 seconds or more, more preferably 20 seconds or more, and even more preferably 40 seconds or more, and is preferably 5 minutes or less, more preferably 3 minutes or less, and even more preferably 2 minutes or less. If the post-exposure bake time is within the above range, the amount of resist residue can be further reduced, while pattern collapse can be sufficiently suppressed.

[0076] <<Vacuum ultraviolet irradiation>> When performing post-exposure treatment by irradiating vacuum ultraviolet rays, the wavelength of the vacuum ultraviolet rays is preferably 10 nm or more, more preferably 100 nm or more, even more preferably 150 nm or more, preferably 200 nm or less, and more preferably 180 nm or less. By using vacuum ultraviolet rays having a wavelength within the above range, the above-mentioned uniformity of the molecular weight distribution in the exposed part of the resist film and the smoothing of the exposed part are further promoted, and the crosslinking reaction of the carbonyl group (-CO-) of the copolymer in the resist film is also promoted, and the amount of resist residue can be further reduced while the pattern collapse can be sufficiently suppressed.

[0077] When performing post-exposure treatment by irradiating with vacuum ultraviolet rays, the irradiation time of the vacuum ultraviolet rays is not particularly limited and can be, for example, from 1 second to 100 seconds. Moreover, the irradiation of the vacuum ultraviolet rays can be performed using a known device.

[0078] <Developing process> In the developing step, the resist film that has been subjected to the post-exposure processing step is developed to form a developed film on the workpiece. Here, the development of the resist film can be carried out, for example, by contacting the resist film with a developer. The method of contacting the resist film with the developer is not particularly limited, and known methods such as immersing the resist film in the developer or applying the developer to the resist film can be used.

[0079] <<Developing conditions>> From the viewpoint of sufficiently improving the clarity of the resist pattern, the development is preferably carried out under conditions where the residual film ratio at an exposure dose of 0.60 Eth exceeds 0.850, and more preferably is 0.900 or greater. From the viewpoint of sufficiently improving the clarity of the resist pattern, the development is preferably carried out under conditions where the residual film ratio at an exposure dose of 0.80 Eth is 0.600 or more, and more preferably 0.700 or more. The developing conditions that satisfy the above-mentioned remaining film ratio can be determined by adjusting the type of developer, the temperature of the developer, the developing time, etc., according to the methods described in Japanese Patent Nos. 6,790,359 and 6,575,141.

[0080] [Developer] The developer can be appropriately selected according to the properties of the copolymer described above. Specifically, when selecting the developer, it is preferable to select a developer that does not dissolve the resist film before the exposure process, but can dissolve the exposed part of the resist film that has been through the exposure process and the post-exposure bake process. In addition, the developer may be used alone or in any ratio of two or more.

[0081] Examples of the developer include hydrofluorocarbons such as 1,1,1,2,3,4,4,5,5,5-decafluoropentane (CF3CFHCFHCF2CF3), 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane, 1,1,1,2,2,3,4,5,5,5-decafluoropentane, 1,1,1,3,3-pentafluorobutane, and 1,1,1,2,2,3,3,4,4-nonafluorohexane; 2,2-dichloro-1,1,1-trifluoroethane; 1,1-dichloro-1-fluoroethane; and 1,1-dichloro-2,2,3,3,3-pentafluorohexane. hydrochlorofluorocarbons such as 1,3-dichloro-1,1,2,2,3-pentafluoropropane (CClF2CF2CHClF) and hydrochlorofluorocarbons such as methyl nonafluorobutyl ether (CF3CF2CF2CF2OCH3), methyl nonafluoroisobutyl ether, ethyl nonafluorobutyl ether (CF3CF2CF2CF2OC2H5), ethyl nonafluoroisobutyl ether, perfluorohexyl methyl ether (CF3CF2CF(OCH3)C3F7), and CF4, C2F6, C3F8, C4F8, C4F 10 , C5F 12 , C6F 12 , C6F 14 , C7F 14 , C7F 16 , C8F 18 , C9F 20Fluorine-based solvents such as perfluorocarbons such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol), 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 1-hexanol, and other alcohols; acetates having an alkyl group such as amyl acetate and hexyl acetate; mixtures of fluorine-based solvents and alcohols; mixtures of fluorine-based solvents and acetates having an alkyl group; mixtures of alcohols and acetates having an alkyl group; mixtures of fluorine-based solvents, alcohols, and acetates having an alkyl group; and the like can be used. Among these, from the viewpoint of more efficiently forming a fine resist pattern with high resolution by EUV lithography, alcohols are preferred, alcohols having 2 to 6 carbon atoms are more preferred, ethanol, isopropyl alcohol, 1-butanol, 2-butanol, 1-pentanol, and 1-hexanol are even more preferred, and isopropyl alcohol is particularly preferred. The developer may be filtered before use, for example by the filtration method using a filter as explained in the above section "Preparation of a positive resist composition".

[0082] [Development time and temperature] The temperature of the developer during development is not particularly limited, but may be, for example, from 21° C. to 25° C. The development time may be, for example, from 15 seconds to 4 minutes.

[0083] <Developer removal process> In the developer removing step optionally included in the method for forming a resist pattern of the present invention, the developer is removed from the developed resist film to form a resist pattern on the workpiece. The developer can be removed by air blowing using a gas such as nitrogen, or by rinsing using a rinsing liquid. Here, in the rinsing process, the method for bringing the developed resist film into contact with a rinsing liquid is not particularly limited, and known methods such as immersing the resist film in a rinsing liquid or applying the rinsing liquid to the resist film can be used.

[0084] The rinse liquid is not particularly limited, and any rinse liquid can be used as long as it can remove the developer and resist residues adhering to the developed resist film.

[0085] The temperature of the rinse liquid during rinsing is not particularly limited, but may be, for example, 21° C. to 25° C. The rinsing time may be, for example, 5 seconds to 3 minutes.

[0086] The above-mentioned rinse liquid may be filtered before use. Examples of the filtration method include the filtration method using a filter explained in the above section "Preparation of a positive resist composition".

[0087] <Pre-irradiation process> In the pre-irradiation step optionally included in the resist pattern forming method of the present invention, the resist film obtained in the resist film forming step is irradiated with vacuum ultraviolet rays prior to the exposure step. By irradiating the resist film with vacuum ultraviolet rays, the strength of the finally obtained resist pattern can be improved and pattern collapse can be suppressed. The wavelength of the vacuum ultraviolet light irradiated onto the resist film and the irradiation time of the vacuum ultraviolet light are not particularly limited, and can be the same as those used in the irradiation of the vacuum ultraviolet light in the "post-exposure treatment step".

[0088] <Post-irradiation process> In the post-irradiation step optionally included in the resist pattern forming method of the present invention, the developed film formed on the workpiece is irradiated with vacuum ultraviolet rays. By irradiating the developed film with vacuum ultraviolet rays, the strength of the finally obtained resist pattern can be improved and pattern collapse can be suppressed. The wavelength of the vacuum ultraviolet light irradiated to the developed film and the irradiation time of the vacuum ultraviolet light are not particularly limited, and can be the same as those used in the irradiation of the vacuum ultraviolet light in the "post-exposure treatment step". In addition, in the case where the method for forming a resist pattern includes the above-described developer removal step, the post-irradiation step may be performed either before or after the developer removal step, or may be performed both before and after the developer removal step, so long as it is performed after the development step.

[0089] (Etching method) A resist pattern obtained by the above-mentioned method for forming a resist pattern can be used as a mask to etch a workpiece (for example, an underlayer film and / or a substrate), thereby forming a pattern on the workpiece. The number of etching steps is not particularly limited, and may be one or more. The etching step may be dry etching or wet etching, but dry etching is preferred. Dry etching can be performed using a known dry etching device. The etching gas used in dry etching can be appropriately selected depending on the elemental composition of the underlayer film and the substrate to be etched. Examples of the etching gas include fluorine-based gases such as CHF3, CF4, C2F6, C3F8, and SF6; chlorine-based gases such as Cl2 and BCl3; oxygen-based gases such as O2, O3, and H2O; reducing gases such as H2, NH3, CO, CO2, CH4, C2H2, C2H4, C2H6, C3H4, C3H6, C3H8, HF, HI, HBr, HCl, NO, NH3, and BCl3; and inert gases such as He, N2, and Ar. These gases may be used alone or in combination of two or more. For dry etching of inorganic underlayer films, oxygen-based gases are usually used. Furthermore, for dry etching of a substrate, a fluorine-based gas is usually used, and a mixture of a fluorine-based gas and an inert gas is preferably used.

[0090] Furthermore, if necessary, the underlayer film remaining on the substrate may be removed before or after etching the substrate. When the underlayer film is removed before etching the substrate, the underlayer film may be a patterned underlayer film or an unpatterned underlayer film.

[0091] Here, the method of removing the underlayer film includes, for example, the above-mentioned dry etching. In addition, in the case of an inorganic underlayer film, a liquid such as a basic liquid or an acid liquid, preferably a basic liquid, may be brought into contact with the underlayer film to remove the underlayer film. Here, the basic liquid is not particularly limited, and examples thereof include alkaline hydrogen peroxide and the like. The method of removing the underlayer film by wet stripping using alkaline hydrogen peroxide is not particularly limited as long as the underlayer film and alkaline hydrogen peroxide can be brought into contact with each other for a certain period of time under heating conditions, and examples thereof include a method of immersing the underlayer film in heated alkaline hydrogen peroxide, a method of spraying alkaline hydrogen peroxide on the underlayer film in a heated environment, and a method of coating the underlayer film with heated alkaline hydrogen peroxide. After performing any of these methods, the substrate is washed with water and dried to obtain a substrate from which the underlayer film has been removed.

[0092] Hereinafter, a series of steps of forming a resist pattern by the above-mentioned resist pattern forming method of the present invention and etching a workpiece (e.g., an underlayer film and / or a substrate) by using the obtained resist pattern as a mask will be described with reference to examples. Note that the resist pattern forming method and etching method of the present invention are not limited to the methods shown in the following examples.

[0093] <First aspect> In the first embodiment, a resist pattern is formed by a resist pattern forming method using EUV, and then etching is performed. Specifically, the first embodiment includes at least an underlayer film forming step, a coating step, a resist film forming step, an exposure step, a development step, a developer removing step, and an etching step.

[0094] First, in the underlayer film forming step, an inorganic material is applied onto a substrate and then baked to form an inorganic underlayer film. Next, in the coating step, a positive resist composition is coated on the inorganic underlayer film formed in the underlayer film forming step. Then, in the resist film forming step, a positive resist composition is applied onto the inorganic underlayer film, and dried to form a resist film. Then, in the exposure process, the resist film formed in the resist film formation process is irradiated with EUV light to draw the desired pattern. Furthermore, in the developing step, the resist film exposed in the exposure step is brought into contact with a developer to develop the resist film, thereby forming a resist pattern on the underlayer film. Then, in the developing solution removal step, the resist film developed in the developing step is brought into contact with a rinsing solution to rinse the developed resist film. Then, in an etching process, the underlying film is etched using the resist pattern as a mask to form a pattern in the underlying film. Next, the substrate is etched using the underlying film on which the pattern is formed as a mask to form a pattern on the substrate.

[0095] <Second aspect> In the second embodiment, a resist pattern is formed by a resist pattern forming method using an electron beam, and then etching is performed. Specifically, the second embodiment includes at least a coating step, a resist film forming step, an exposure step, a development step, a developer removing step, and an etching step.

[0096] First, in the coating step, a positive resist composition is coated onto a substrate. Next, in the resist film forming step, the positive resist composition on the substrate is dried to form a resist film. Then, in the exposure step, the resist film formed in the resist film forming step is irradiated with an electron beam to draw a desired pattern. Furthermore, in the development step, the resist film exposed in the exposure step is brought into contact with a developer to develop the resist film, thereby forming a resist pattern on the substrate. Then, in the developing solution removal step, the resist film developed in the developing step is brought into contact with a rinsing solution to rinse the developed resist film. Then, in an etching process, the substrate is etched using the resist pattern as a mask to form a pattern on the substrate. EXAMPLES

[0097] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following description, "%" representing an amount is based on mass unless otherwise specified. In the examples and comparative examples, the weight average molecular weight, number average molecular weight and molecular weight distribution of the copolymer, and the proportion of components of each molecular weight in the copolymer were measured by the following methods.

[0098] <Weight average molecular weight, number average molecular weight and molecular weight distribution> The weight average molecular weight (Mw) and number average molecular weight (Mn) of the copolymers obtained in the examples and comparative examples were measured using gel permeation chromatography, and the molecular weight distribution (Mw / Mn) was calculated. Specifically, a gel permeation chromatograph (Tosoh Corporation, HLC-8220) was used, and tetrahydrofuran was used as a developing solvent to determine the weight average molecular weight (Mw) and number average molecular weight (Mn) of the polymer in terms of standard polystyrene. Then, the molecular weight distribution (Mw / Mn) was calculated. <Proportion of each molecular weight component in the copolymer> A chromatogram of the copolymer was obtained using gel permeation chromatography (Tosoh Corporation, HLC-8220) and tetrahydrofuran as a developing solvent. From the obtained chromatogram, the total peak area (A), the sum of the peak areas of components with molecular weights of less than 10,000 (B), the sum of the peak areas of components with molecular weights of less than 50,000 (C), the sum of the peak areas of components with molecular weights of less than 100,000 (D), and the sum of the peak areas of components with molecular weights of more than 200,000 (E) were calculated. The proportion of each molecular weight component was calculated using the following formula. Percentage of components with molecular weight less than 10,000 (%) = (B / A) x 100 Percentage of components with molecular weight less than 50,000 (%) = (C / A) x 100 Percentage of components with molecular weight less than 100,000 (%) = (D / A) x 100 Percentage of components with molecular weights over 200,000 (%) = (E / A) x 100

[0099] Example 1 <Preparation of Copolymer> <<Preparation of an aqueous solution of partially hardened beef tallow fatty acid potassium soap with a solid content of 18%>> 100g of ion-exchanged water was prepared, heated to 70°C while stirring, and 8.40g of potassium hydroxide (49% aqueous solution) was added. Next, 19.6g of beef tallow 45° hardened fatty acid HFA (NOF Corp.) was added at a rate of 1.28g / min, and then 0.126g of potassium silicate was added. The mixture was stirred at 80°C for more than 2 hours to obtain an aqueous solution of semi-hardened beef tallow fatty acid potassium soap with a solid content of 18%. <<Synthesis of Polymers>> In a glass ampoule containing a stirrer, 3.00 g of α-chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (see formula below) as monomer (a) and 1.066 g of α-methylstyrene as monomer (b) were added. In addition, 6.771 g of ion-exchanged water was added to 0.5463 g of the aqueous solution of the semi-hardened beef tallow fatty acid potassium soap with a solid content of 18% prepared above to prepare a monomer composition, and the ampoule was sealed and pressurized and depressurized with nitrogen gas 10 times to remove oxygen from the system. [ka] The system was then heated to 75°C and polymerization reaction was carried out for 1 hour. Next, 10g of tetrahydrofuran was added to the system, and the resulting solution was dropped into 300mL of methanol to precipitate a polymer. The precipitated polymer was then collected by filtration. The resulting polymer was a copolymer containing 50 mol% each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units. [Purification of polymer] The polymer recovered by filtration was then dissolved in 10 g of tetrahydrofuran (THF), and the resulting solution was dropped into 100 g of a mixed solvent of THF and methanol (MeOH) (THF:MeOH (mass ratio) = 30:70), and a white coagulated product (a copolymer containing α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units) was precipitated. The solution containing the precipitated copolymer was then filtered using a Kiriyama funnel to obtain a white copolymer. Next, the polymer recovered by filtration was dissolved in 10 g of THF, and the resulting solution was dropped into 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) = 33:67), and a white coagulated product was precipitated. Furthermore, the polymer recovered by filtration was dissolved in 10 g of THF, and the obtained solution was added dropwise to 100 g of a mixed solvent of THF and MeOH (THF:MeOH (mass ratio) = 33:67) to precipitate a white coagulant (a copolymer containing α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units). The resulting copolymer had a weight average molecular weight of 363,867, a number average molecular weight of 267,588 and a molecular weight distribution of 1.360. The proportions of components with different molecular weights in the resulting copolymer were as follows: Percentage of components with molecular weight less than 10,000 (%) = 0.00% Percentage of components with molecular weight less than 50,000 (%) = 0.10% Percentage of components with molecular weight less than 100,000 (%) = 1.69% Percentage of components with molecular weights over 200,000 (%) = 87.68% <Preparation of Positive Resist Composition> The obtained copolymer was dissolved in isoamyl acetate (manufactured by Tokyo Chemical Industry Co., Ltd.) as a solvent to prepare a resist solution (positive resist composition) with a copolymer concentration of 2 mass %. <Creating a sensitivity curve> Using a spin coater (MS-A150, manufactured by Mikasa), the positive resist composition was applied onto a silicon wafer with a diameter of 4 inches (application step). The applied positive resist composition was then heated on a hot plate at a temperature of 120°C for 1 minute to form a resist film on the silicon wafer (resist film formation step). The thickness of the resist film was 50 nm. The weight average molecular weight and number average molecular weight of the copolymer contained in the resist film, as well as the density of the resist film (film density), were measured. The weight average molecular weight and molecular weight distribution after pre-baking, as well as the film density, are shown in Table 1. Then, using an electron beam lithography device (ELS-S50, manufactured by Elionix), multiple patterns (dimensions 500 μm×500 μm) with different doses of electron beam were written on the resist film (exposure process), and the exposed resist film was heated on a hot plate at 90° C. for 1 minute (post-exposure process). The resist film after the post-exposure process was developed at 23° C. for 1 minute using isopropyl alcohol as a developer (development process). Thereafter, the developer was removed by nitrogen blowing to form a resist pattern (developer removal process). The electron beam dose was 4 μC / cm 2 to 200μC / cm 2 Within the range of 4μC / cm 2 Each was made different. Next, the thickness of the resist film in the written area was measured with an optical film thickness meter (Lambda Ace, manufactured by SCREEN Semiconductor Solutions), and a sensitivity curve was created showing the relationship between the common logarithm of the total electron beam irradiation dose and the remaining film rate of the resist film after development (= (film thickness of the resist film after development / film thickness of the resist film formed on the silicon wafer). <Clarity (γ value)> For the sensitivity curve obtained as described above (horizontal axis: common logarithm of the total electron beam irradiation dose, vertical axis: remaining film ratio of the resist film (0 ≤ remaining film ratio ≤ 1.00)), the γ value was determined using the following formula. In the following formula, E0 is the logarithm of the total irradiation dose obtained when substituting 0 for the remaining film ratio in the quadratic function obtained by fitting the sensitivity curve to a quadratic function in the range of the remaining film ratio of 0.20 to 0.80 (function of the remaining film ratio and the common logarithm of the total irradiation dose). Also, E1 is the logarithm of the total irradiation dose obtained when substituting 1.00 for the remaining film ratio in the straight line (approximate line of the slope of the sensitivity curve) connecting the point with a remaining film ratio of 0 and the point with a remaining film ratio of 0.50 on the obtained quadratic function (function of the remaining film ratio and the common logarithm of the total irradiation dose). And the following formula represents the slope of the above straight line between the remaining film ratios of 0 and 1.00. [Number] The larger the value of the γ value, the larger the slope of the sensitivity curve, indicating that a pattern with high clarity can be formed well. <Eth, remaining film ratios at irradiation doses of 0.60Eth and 0.80Eth> The total electron beam irradiation dose Eth (μC / cm 2 ) was determined when the remaining film ratio of the straight line (approximate line of the slope of the sensitivity curve) obtained during the calculation of the above γ value becomes 0. Then, from the sensitivity curve, the remaining film ratio at an irradiation dose of 0.60Eth and the remaining film ratio at an irradiation dose of 0.80Eth were read. The results are shown in Table 1. <Amount of resist residue (residue reduction)> The above sensitivity curve was used for evaluation as follows. The minimum value of the absolute value of the slope of the tangent line of the sensitivity curve in the range where the remaining film ratio exceeds 0.2 and is 0.8 or less (the first range) is S1, and the minimum value of the absolute value of the slope of the tangent line of the sensitivity curve in the range where the remaining film ratio is 0.2 or less (the second range) is S2. S1 and S2 were compared and evaluated according to the following criteria. Note that S2 being less than or equal to S1 means that there is a shoulder in the second range of the sensitivity curve and there is a large amount of resist residue. A: S2 > S1 B: S2 ≤ S1 <Pattern collapse suppression> Using a spin coater (MS-A150, manufactured by Mikasa), the positive resist composition was applied to a silicon wafer having a diameter of 4 inches to a thickness of 50 nm (application step). Next, the applied positive resist composition was heated on a hot plate at a temperature of 120° C. for 1 minute to form a resist film on the silicon wafer (resist film formation step). The resist film had a thickness of 50 nm. Then, the resist film was exposed to an optimum exposure dose (Eop) using an electron beam lithography device (ELS-S50, manufactured by Elionix) to draw a pattern (exposure step). The exposed resist film was heated on a hot plate at 90° C. for 1 minute (post-exposure treatment step). The resist film after the post-exposure treatment was subjected to a development treatment at a temperature of 23° C. for 1 minute using isopropyl alcohol as a developer (development step). Then, the developer was removed by nitrogen blowing to form a resist pattern (developer removal step). The resist patterns were then observed for pattern collapse. The optimum exposure dose (Eop) was appropriately set to approximately twice the Eth. The lines (unexposed areas) and spaces (exposed areas) of the resist pattern were each set to 20 nm. The suppression of pattern collapse was evaluated according to the following criteria. A: No pattern collapse B: Pattern collapsed

[0100] (Examples 2 to 121) Except for changing at least one of the pre-bake temperature, pre-bake time, post-exposure bake temperature, and post-exposure bake time as shown in Tables 1 to 4, the preparation of a copolymer, the preparation of a positive resist composition, and the formation of a resist pattern were carried out in the same manner as in Example 1, and various evaluations were carried out in the same manner as in Example 1. The results are shown in Tables 1 to 4.

[0101] (Comparative Examples 1 to 64) Except for changing at least one of the pre-bake temperature, pre-bake time, post-exposure bake temperature and post-exposure bake time as shown in Tables 5 and 6, or not performing post-exposure treatment (post-exposure bake), the copolymer was prepared, the positive resist composition was prepared and the resist pattern was formed in the same manner as in Example 1, and various evaluations were performed in the same manner as in Example 1. The results are shown in Tables 5 and 6. In Comparative Example 1, since the pre-bake temperature was low at 90° C., the solvent could not be sufficiently removed in the resist film forming step, and a good resist film could not be formed. In addition, in Comparative Examples 13, 25, 28, 31, 34, 37, 40, 43, 46, 49, 51, 53, 55, 57, 59, 61, and 63, the post-exposure bake temperature was high at 160° C., so that the resist pattern disappeared in the development step. Furthermore, in Comparative Example 64, the pre-bake temperature was as high as 260° C., so that the copolymer was carbonized in the resist film forming process, and a good resist film could not be formed.

[0102] In addition, the "film reduction rate" of the resist film shown in each table is calculated as film reduction rate (%) = (50 - T) / 50 × 100, where T is the thickness of the resist film obtained in the resist film formation process in each Example and Comparative Example, and T is the thickness of the resist film in Example 1 (50 nm).

[0103] [Table 1]

[0104] [Table 2]

[0105] [Table 3]

[0106] [Table 4]

[0107] [Table 5]

[0108] [Table 6]

[0109] It can be seen from Tables 1 to 4 that in Examples 1 to 121, resist patterns with excellent clarity and reduced amounts of resist residues could be formed, and that in Examples 1 to 121, collapse of the resist pattern could be suppressed. [Industrial Applicability]

[0110] According to the method of forming a resist pattern of the present invention, the amount of resist residue can be reduced while ensuring the clarity of the resulting resist pattern.

Claims

1. A method for producing a positive resist composition comprising: applying a copolymer containing α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units, and a solvent, onto a workpiece; a step of drying the positive resist composition applied onto the workpiece at a temperature of 120° C. or higher and 250° C. or lower to form a resist film; exposing the resist film to light; a step of performing a post-exposure treatment on the resist film after the exposure, the post-exposure treatment including heating the resist film at a temperature of 90° C. or more and 150° C. or less; developing the resist film after the post-exposure treatment; A method for forming a resist pattern comprising the steps of:

2. The method for forming a resist pattern according to claim 1 , wherein the developing is carried out under conditions such that a residual film ratio at an exposure dose of 0.60 Eth exceeds 0.

850.

3. 3. The method for forming a resist pattern according to claim 1, wherein the developing is carried out under conditions such that a residual film ratio at an exposure dose of 0.80 Eth is 0.600 or more.

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