Resist composition and pattern forming method

Abstract

To provide a resist composition which is excellent in sensitivity, resolution, and LWR, is stable, and is easy to handle in photolithography using a high-energy ray, and to provide a pattern forming method using the resist composition.SOLUTION: A resist composition comprises a zinc tetranuclear cluster.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] As the IoT market expands, there is a growing demand for higher integration, higher speeds, and lower power consumption in LSIs, leading to rapid progress in miniaturization of pattern rules. Logic devices, in particular, are driving this miniaturization. The most advanced miniaturization technology is ArF immersion lithography, with double patterning, triple patterning, and quadruple patterning being used to mass-produce 10nm-node devices, and studies are underway to develop 7nm-node devices using next-generation extreme ultraviolet (EUV) lithography with a wavelength of 13.5nm.

[0003] As miniaturization progresses, image blurring due to acid diffusion has become a problem (Non-Patent Document 1). It has been suggested that in order to ensure resolution in fine patterns for the 45-nm generation and beyond, not only is it important to improve dissolution contrast, as has been proposed previously, but also to control acid diffusion (Non-Patent Document 2). However, because chemically amplified resist compositions increase sensitivity and contrast through acid diffusion, attempts to minimize acid diffusion by lowering the post-exposure bake (PEB) temperature or shortening the PEB time result in significant decreases in sensitivity and contrast.

[0004] Adding an acid generator that generates bulky acid is effective in suppressing acid diffusion. Therefore, copolymerization of an onium salt acid generator with a polymerizable olefin into a polymer has been proposed. However, for resist film pattern formation for feature sizes of 16 nm and beyond, it is believed that chemically amplified resist compositions cannot be used to form patterns due to acid diffusion, and the development of non-chemically amplified resist compositions is desired.

[0005] One material for non-chemically amplified resist compositions is polymethyl methacrylate (PMMA). PMMA is a positive resist material whose main chain is cleaved by electron beam (EB) or EUV irradiation, reducing its molecular weight and improving its solubility in organic solvent developers. However, because it does not have a ring structure, it has the disadvantages of low etching resistance and large outgassing during exposure.

[0006] Hydrogen silsesquioxane (HSQ) is a material used in negative resist compositions that becomes insoluble in alkaline developers due to crosslinking caused by condensation of silanols generated by EB or EUV irradiation. Chlorine-substituted calixarenes also function as materials for negative resist compositions. These materials have small molecular size before crosslinking and are free of blurring due to acid diffusion, resulting in low edge roughness and extremely high resolution. They are therefore used as pattern transfer materials to indicate the resolution limit of exposure equipment. However, these materials have insufficient sensitivity, and further improvement is needed.

[0007] One of the challenges in developing materials for EUV lithography is the low photon count in EUV exposure. EUV energy is much higher than that of ArF excimer laser light, and the photon count in EUV exposure is one-fourteenth that of ArF exposure. Furthermore, the pattern dimensions formed with EUV exposure are less than half those of ArF exposure. This makes EUV exposure susceptible to variations in photon count. The variations in photon count in the extremely short wavelength radiation region are a physical phenomenon known as shot noise, and this effect cannot be eliminated. Therefore, so-called stochastics has attracted attention. While the effects of shot noise cannot be eliminated, methods for reducing this effect are being discussed. Shot noise not only increases dimensional uniformity (CDU) and line width roughness (LWR), but also causes hole blockage with a probability of one in several million. Blocked holes cause poor electrical conduction, preventing transistor operation and adversely affecting overall device performance.

[0008] As a method for reducing the effects of shot noise on the resist side, inorganic resist compositions containing elements with high EUV absorption have been proposed (Patent Document 1). However, although inorganic resist compositions have relatively high sensitivity, they are still not sufficient and have many issues, such as insufficient solubility in solvents used in resist compositions, storage stability, and defects.

[0009] Non-Patent Document 3 proposes a negative resist composition that uses a tin compound. This is a non-chemically amplified resist composition whose main component is tin, which has high EUV light absorption. Although the stochastics have been improved and sensitivity and resolution have been greatly improved, the composition has problems with stability, and its performance changes depending on the time elapsed after PEB (Post PEB Delay: PPD) after PEB. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-108781 [Non-patent literature]

[0011] [Non-Patent Document 1] SPIE Vol.5039 p1 (2003) [Non-patent document 2] SPIE Vol.6520 p65203L-1 (2007) [Non-patent document 3] SPIE Vol.9051 p90511B-1 (2014) Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a resist composition that is stable and easy to handle, and that exhibits excellent sensitivity, resolution, and LWR in photolithography using high-energy rays, particularly in EB lithography and EUV lithography, and a pattern formation method that uses the resist composition. [Means for solving the problem]

[0013] As a result of extensive research into achieving the above-mentioned object, the inventors of the present invention have discovered that a resist composition containing a tetranuclear zinc cluster as a main component is highly sensitive, exhibits excellent resolution and LWR, and also provides a resist film with excellent stability, making it extremely effective for precise microfabrication, leading to the completion of the present invention.

[0014] That is, the present invention provides the following resist composition and pattern forming method. 1. A resist composition containing a zinc tetranuclear cluster. 2. The resist composition of 1, wherein the zinc tetranuclear cluster is represented by the following formula (1): [ka] (In the formula, R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each independently a hydrogen atom or a hydrocarbyl group having 1 to 20 carbon atoms which may contain a heteroatom. 3. The resist composition of 2, wherein the zinc tetranuclear cluster is represented by the following formula (2): [ka] (In the formula, R 11 , R 12 , R 13 , R 14 , R 15 and R 16 are each independently a crosslinkable group-containing group having 1 to 20 carbon atoms.) 4. The resist composition according to any one of 1 to 3, further comprising a carboxylic acid compound. 5. The resist composition according to any one of 1 to 4, further comprising a photoacid generator. 6. A pattern forming method comprising the steps of forming a resist film on a substrate using a resist composition according to any one of 1 to 5, exposing the resist film to high-energy rays, and developing the exposed resist film to form a resist pattern. 7. The pattern formation method according to claim 6, wherein the high-energy radiation is EB or EUV. [Effects of the Invention]

[0015] The resist composition of the present invention is extremely useful for forming fine patterns, particularly in EB lithography and EUV lithography, because it combines high sensitivity and high resolution, has excellent LWR, and also has good stability. DETAILED DESCRIPTION OF THE INVENTION

[0016] [Resist composition] The resist composition of the present invention contains a tetranuclear zinc cluster.

[0017] [Tetranuclear zinc cluster] The synthesis of zinc tetranuclear clusters has been reported in the past. For example, in J. Am. Chem. Soc. 2008, 130, 2944, a zinc tetranuclear cluster Zn4(OCOCF3) with trifluoroacetic acid as a ligand was synthesized. 6O A transesterification reaction using this cluster has been reported. This cluster not only has excellent catalytic activity, but also has the advantage of being easy to synthesize.

[0018] Furthermore, zinc has a high absorption efficiency for EUV light, so the application of zinc tetranuclear clusters, which are easy to prepare and have a high absorption capacity for EUV light, to EUV lithography can be said to be very effective.

[0019] The zinc tetranuclear cluster is preferably one represented by the following formula (1). [ka]

[0020] In formula (1), R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each independently a hydrogen atom or a hydrocarbyl group having 1 to 20 carbon atoms which may contain a heteroatom. The hydrocarbyl group having 1 to 20 carbon atoms may be saturated or unsaturated and may be linear, branched, or cyclic. Specific examples thereof include alkyl groups having 1 to 20 carbon atoms such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, tert-pentyl, n-hexyl, n-octyl, 2-ethylhexyl, n-nonyl, and n-decyl; cyclopentyl, cyclohexyl, cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl, norbornyl, and tricyclo[5.2.1.0]. 2,6 ] cyclic saturated hydrocarbyl groups having 3 to 20 carbon atoms such as decanyl, adamantyl, and adamantylmethyl; alkenyl groups having 2 to 20 carbon atoms such as vinyl and 2-propenyl; aryl groups having 6 to 20 carbon atoms such as phenyl and naphthyl; and groups obtained by combining these. In addition, some or all of the hydrogen atoms in the hydrocarbyl groups may be substituted with groups containing heteroatoms such as oxygen, sulfur, nitrogen, and halogen atoms, and some of the -CH2- in the hydrocarbyl groups may be substituted with groups containing heteroatoms such as oxygen, sulfur, and nitrogen atoms, so that the hydrocarbyl groups may contain hydroxy groups, cyano groups, halogen atoms, carbonyl groups, ether bonds, thioether bonds, ester bonds, sulfonate ester bonds, carbonate bonds, carbamate bonds, lactone rings, sultone rings, carboxylic anhydrides (-C(=O)-OC(=O)-), and the like.

[0021] The zinc tetranuclear cluster is more preferably one represented by the following formula (2). [ka]

[0022] In formula (2), R 11 , R 12 , R 13 , R 14 , R 15 and R 16 are each independently a crosslinkable group-containing group having 1 to 20 carbon atoms. Examples of the crosslinkable group include a substituent having a double bond or a triple bond and a substituent having a cyclic ether structure. Specific examples of the crosslinkable group-containing group include a vinyl group, a 1-propenyl group, a 2-propenyl group, an isopropenyl group, an ethynyl group, a 1-(trifluoromethyl)vinyl group, a vinylphenyl group, a glycidyl group, and an oxetanylmethyl group. Clusters having such crosslinkable groups undergo a crosslinking reaction upon exposure, and as a result, the exposed portion has strong development resistance, thereby increasing contrast and further improving resolution.

[0023] Specific examples of the zinc tetranuclear cluster include, but are not limited to, the following: [ka]

[0024] [ka]

[0025] [ka]

[0026] The zinc tetranuclear clusters may be used alone or in combination of two or more.

[0027] [Organic solvents] The resist composition of the present invention contains an organic solvent. The organic solvent is not particularly limited as long as it can dissolve the zinc tetranuclear cluster and form a film. Examples of such organic solvents include ketones such as cyclohexanone and methyl-2-n-pentyl ketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, and diacetone alcohol; ethers such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, propylene glycol dimethyl ether, and diethylene glycol dimethyl ether; and propylene glycol monomethyl ether. Examples of suitable solvents include esters such as propylene glycol monoethyl ether acetate (PGMEA), propylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, methyl 2-hydroxyisobutyrate, tert-butyl acetate, cyclohexyl acetate, tert-butyl propionate, and propylene glycol mono-tert-butyl ether acetate; lactones such as γ-butyrolactone; carboxylic acids such as acetic acid and propionic acid; aromatics such as toluene, xylene, cresol, anisole, and benztrifluoride; and mixed solvents thereof.

[0028] The content of the organic solvent is preferably 200 to 20,000 parts by mass, more preferably 500 to 15,000 parts by mass, relative to 100 parts by mass of the zinc tetranuclear cluster.

[0029] The resist composition of the present invention is believed to exhibit contrast due to the change in development resistance between exposed and unexposed areas caused by photodecomposition of the zinc tetranuclear cluster, the main component, followed by an aggregation or crosslinking reaction between the partially destroyed clusters. Because this reaction is not catalytic, the resist composition of the present invention functions as a non-chemically amplified resist composition. Therefore, it is possible to resolve fine areas that are difficult to pattern using conventional chemically amplified resist compositions primarily composed of multi-component polymers. In particular, for EUV lithography, the zinc atoms have high EUV absorption, resulting in improved stochastics and a resist composition with excellent sensitivity and LWR. Furthermore, the zinc tetranuclear cluster has a thermally stable structure, resulting in excellent storage stability. Furthermore, there is no significant change in performance over time after PEB.

[0030] [Photoacid generator] The resist composition of the present invention may contain a photoacid generator as an additional component in addition to the zinc tetranuclear cluster and organic solvent. The use of a photoacid generator is expected to generate acid in exposed areas and promote the crosslinking reaction of the zinc compound. Such photoacid generators are not particularly limited as long as they generate acid upon irradiation with high-energy rays. Known photoacid generators for conventional chemically amplified resist compositions can be used, but those that generate sulfonic acid, imide acid, or methide acid are particularly preferred. Suitable photoacid generators include sulfonium salts, iodonium salts, sulfonyldiazomethane, N-sulfonyloxyimide, and oxime-O-sulfonate-type acid generators. Specific examples of the photoacid generator include those described in paragraphs

[0122] to

[0142] of JP 2008-111103 A and those described in paragraphs

[0127] to

[0193] of JP 2022-163697 A.

[0031] When the resist composition of the present invention contains the photoacid generator, its content is preferably 0.01 to 20 mass% of the total solid content. In the present invention, the solid content collectively refers to all components of the resist composition other than the solvent. The photoacid generator may be used alone or in combination of two or more.

[0032] [Carboxylic acid compounds] The resist composition of the present invention may contain a carboxylic acid compound as another component. By performing a film formation process in the presence of a carboxylic acid compound in the zinc tetranuclear cluster, some of the ligands in the cluster can be replaced with the coexisting carboxylic acid compound, thereby adjusting the lithography performance. Examples of such carboxylic acid compounds include, but are not limited to, carboxylic acids that can be precursors of the ligands of the zinc tetranuclear cluster.

[0033] When the resist composition of the present invention contains the carboxylic acid compound, the content thereof is preferably 1 to 200 mass % of the total solid content. The carboxylic acid compound may be used alone or in combination of two or more.

[0034] [Radical scavengers] The resist composition of the present invention may further contain a radical scavenger as an additional component. By adding a radical scavenger, it is possible to control the photoreaction during photolithography and adjust the sensitivity.

[0035] Examples of the radical scavenger include hindered phenols, quinones, hindered amines, and thiol compounds. Specific examples of the hindered phenols include dibutylhydroxytoluene and 2,2'-methylenebis(4-methyl-6-tert-butylphenol). Specific examples of the quinones include 4-methoxyphenol (methoquinone) and hydroquinone. Specific examples of the hindered amines include 2,2,6,6-tetramethylpiperidine and 2,2,6,6-tetramethylpiperidine-N-oxy radical. Specific examples of the thiols include dodecanethiol and hexadecanethiol.

[0036] When the resist composition of the present invention contains the radical scavenger, the content thereof is preferably 0.01 to 10 mass % of the total solid content. The radical scavenger may be used alone or in combination of two or more.

[0037] [Surfactants] The resist composition of the present invention may contain a surfactant as another component. Examples of the surfactant include those described in JP-A-2010-215608 and JP-A-2011-16746. Among these, preferred surfactants include FC-4430 (manufactured by 3M), Surflon (registered trademark) S-381 (manufactured by AGC Seimi Chemical Co., Ltd.), Olfine (registered trademark) E1004 (manufactured by Nissin Chemical Industry Co., Ltd.), KH-20, KH-30 (manufactured by AGC Seimi Chemical Co., Ltd.), and an oxetane ring-opening polymer represented by the following formula (surf-1): [ka]

[0038] In formula (surf-1), R represents a divalent to tetravalent aliphatic group having 2 to 5 carbon atoms. Examples of the divalent aliphatic group include an ethylene group, a 1,4-butylene group, a 1,2-propylene group, a 2,2-dimethyl-1,3-propylene group, and a 1,5-pentylene group, and examples of the trivalent or tetravalent aliphatic group include the following: [ka] (In the formula, the dashed lines represent bonds and are partial structures derived from glycerol, trimethylolethane, trimethylolpropane, and pentaerythritol, respectively.)

[0039] Among these, a 1,4-butylene group, a 2,2-dimethyl-1,3-propylene group, and the like are preferred.

[0040] Rf is a trifluoromethyl group or a pentafluoroethyl group, preferably a trifluoromethyl group. m is an integer of 0 to 3, n is an integer of 1 to 4, and the sum of n and m is the valence of R, which is an integer of 2 to 4. A is 1. B is an integer of 2 to 25, preferably an integer of 4 to 20. C is an integer of 0 to 10, preferably 0 or 1. The order of the structural units in formula (surf-1) is not specified, and they may be bonded in blocks or randomly. The production of partially fluorinated oxetane ring-opening polymer surfactants is described in detail in the specification of U.S. Pat. No. 5,650,483, etc.

[0041] When the resist composition of the present invention contains the surfactant, the content thereof is preferably 0.001 to 20 parts by mass, and more preferably 0.1 to 10 parts by mass, relative to 100 parts by mass of the zinc tetranuclear cluster. The surfactants may be used alone or in combination of two or more.

[0042] [Pattern formation method] When the resist composition of the present invention is used in the manufacture of various integrated circuits, known lithography techniques can be applied. For example, a pattern formation method can include a method comprising the steps of forming a resist film on a substrate using the resist composition, exposing the resist film to high-energy rays, and developing the exposed resist film.

[0043] First, the resist composition of the present invention is applied to a substrate for integrated circuit production (Si, SiO2, SiN, SiON, TiN, WSi, BPSG, SOG, organic antireflective coating, etc.) or a substrate for mask circuit production (Cr, CrO, CrON, MoSi2, SiO2, etc.) by an appropriate coating method such as spin coating, roll coating, flow coating, dip coating, spray coating, doctor coating, etc., to a coating thickness of 0.01 to 2 μm. This is then heated on a hot plate, preferably at 60 to 200°C for 10 seconds to 30 minutes, more preferably at 80 to 180°C for 30 seconds to 20 minutes, to form a resist film.

[0044] Next, the resist film is exposed to high-energy radiation. Examples of the high-energy radiation include ultraviolet radiation, far ultraviolet radiation, EB, EUV radiation with a wavelength of 3 to 15 nm, X-rays, soft X-rays, excimer laser light, gamma rays, and synchrotron radiation. When ultraviolet radiation, far ultraviolet radiation, EUV radiation, X-rays, soft X-rays, excimer laser light, gamma rays, and synchrotron radiation are used as the high-energy radiation, the exposure dose is preferably 1 to 200 mJ / cm, either directly or using a mask for forming a desired pattern. 2 approximately, more preferably 10 to 150 mJ / cm 2 When EB is used as the high energy beam, the exposure dose is preferably 0.1 to 5000 μC / cm 2 either directly or using a mask for forming a desired pattern. 2 approximately, more preferably 0.5 to 4000 μC / cm 2 The resist composition of the present invention is particularly suitable for fine patterning using high-energy rays such as EB or EUV.

[0045] To accelerate or complete the reaction after photodecomposition, PEB may be performed. When PEB is performed, it is preferably performed on a hot plate or in an oven after exposure, preferably at 30 to 200°C for 10 seconds to 30 minutes, more preferably at 60 to 180°C for 30 seconds to 20 minutes.

[0046] The development method performed after exposure or PEB may be either wet development or dry development. For wet development, alkali development or organic solvent development can be used, but organic solvent development is preferred when forming a pattern using the resist composition of the present invention. Wet development is performed on the exposed resist film by a conventional method such as dipping, puddling, or spraying, preferably for 3 seconds to 3 minutes, more preferably 5 seconds to 2 minutes, to form the desired pattern. Since the resist composition of the present invention is negative, the irradiated portions are insolubilized in the developer, while the unexposed portions are soluble.

[0047] The organic solvents used as developers include 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone, methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, butenyl acetate, isopentyl acetate, propyl formate, cyclohexyl acetate, butyl formate, isobutyl formate, pentyl formate, isopentyl formate, methyl valerate, methyl pentenoate, methyl crotonate, methyl chloroform ... Examples of organic solvents include ethyl lactate, methyl propionate, ethyl propionate, ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate, propyl lactate, butyl lactate, isobutyl lactate, pentyl lactate, isopentyl lactate, methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methyl benzoate, ethyl benzoate, phenyl acetate, benzyl acetate, methyl phenylacetate, ethyl phenylacetate, benzyl formate, phenylethyl formate, methyl 3-phenylpropionate, benzyl propionate, and 2-phenylethyl acetate. These organic solvents may be used alone or in combination of two or more.

[0048] After development, rinsing may be performed as necessary. A preferred rinsing solution is a solvent that is miscible with the developer but does not dissolve the resist film. Preferred examples of such solvents include alcohols having 3 to 10 carbon atoms, ether compounds having 8 to 12 carbon atoms, alkanes, alkenes, alkynes, and aromatic solvents having 6 to 12 carbon atoms.

[0049] Specific examples of the alcohol having 3 to 10 carbon atoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol, 2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, tert-pentyl alcohol, neopentyl alcohol, 2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol, cyclopentanol, 1-hexanol, 2-hexanol, and 3-hexanol. Examples of the alcohol include 2,3-dimethyl-2-butanol, 3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol, 2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol, 4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol, cyclohexanol, and 1-octanol.

[0050] Specific examples of the ether compound having 8 to 12 carbon atoms include di-n-butyl ether, diisobutyl ether, di-sec-butyl ether, di-n-pentyl ether, diisopentyl ether, di-sec-pentyl ether, di-tert-pentyl ether, and di-n-hexyl ether.

[0051] Specific examples of the alkanes having 6 to 12 carbon atoms include hexane, heptane, octane, nonane, decane, undecane, dodecane, methylcyclopentane, dimethylcyclopentane, cyclohexane, methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, cyclononane, etc. Specific examples of the alkenes having 6 to 12 carbon atoms include hexene, heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene, cycloheptene, cyclooctene, etc. Specific examples of the alkynes having 6 to 12 carbon atoms include hexyne, heptine, octyne, etc.

[0052] Specific examples of the aromatic solvent include toluene, xylene, ethylbenzene, isopropylbenzene, tert-butylbenzene, and mesitylene.

[0053] Rinsing can reduce the occurrence of resist pattern collapse and defects. Rinsing is not always necessary, and not performing rinsing can reduce the amount of solvent used.

[0054] Dry development can also be used as a development method in the pattern formation method of the present invention. Dry development is a development in which either the exposed or unexposed areas are removed by a gas etching process without using a developer. In the present invention, the desired pattern can be formed by removing the unexposed areas with an etching gas. For dry etching, a gas containing oxygen, hydrogen, ammonia, halogen, or the like, and a gas containing nitrogen, helium, argon, carbon dioxide, or carbon monoxide as a diluent is preferably used. [Example]

[0055] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0056] The tetranuclear zinc clusters used in the examples are represented by the following formulae (M-1) to (M-3). [ka]

[0057] As the zinc tetranuclear cluster (M-1), ZnTAC24 (registered trademark) manufactured by Tokyo Chemical Industry Co., Ltd. was used.

[0058] [1] Synthesis of tetranuclear zinc cluster [Synthesis Example 1] Synthesis of tetranuclear zinc cluster (M-2) 0.96 g of zinc tetranuclear cluster (M-1), 2.6 g of crotonic acid, and 30 g of toluene were mixed and stirred for 1 hour, and then the reaction solution was concentrated under reduced pressure. The concentrated residue was added to n-hexane and purified by recrystallization to obtain 0.71 g of zinc tetranuclear cluster (M-2).

[0059] [Synthesis Example 1] Synthesis of zinc tetranuclear cluster (M-3) 0.96 g of zinc tetranuclear cluster (M-1), 3.4 g of 3-oxetaneacetic acid, and 30 g of toluene were mixed and stirred for 1 hour, and then the reaction solution was concentrated under reduced pressure. The concentrated residue was added to n-hexane and purified by recrystallization to obtain 0.89 g of zinc tetranuclear cluster (M-3).

[0060] [2] Preparation of resist composition [Examples 1-1 to 1-7, Comparative Example 1-1] Resist compositions R-1 to R-7 of the present invention and comparative resist composition CR-1 were prepared by dissolving each component in a solvent according to the composition shown in Table 1 below, and filtering the resulting solution through a 0.2 μm Teflon (registered trademark) filter.

[0061] [Table 1]

[0062] In Table 1, component A is a metal cluster, component B is a photoacid generator, component C is a carboxylic acid compound, and component D is a radical scavenger. The structures of the zinc tetranuclear clusters (M-1) to (M-3) used as component A are as described above. Details of components B to D and the solvent are as follows:

[0063] P-1: Triphenylsulfonium tosylate CA-1: 4-vinylbenzoic acid CA-2: Propargylic acid Sc-1: Dibutylhydroxytoluene PGMEA: Propylene glycol monomethyl ether acetate

[0064] In Table 1, CM-1 (tin compound) used in the comparative examples was synthesized according to Angewandte Chemie, International Edition (2017), 56(34), 10140-10144. The structure of CM-1 is as follows. [ka]

[0065] [3] EB lithography evaluation [Examples 2-1 to 2-7, Comparative Example 2-1] Each resist composition (R-1 to R-7, CR-1) was spin-coated onto a Si substrate coated with a 60-nm-thick anti-reflective coating (DUV-42, manufactured by Nissan Chemical Industries, Ltd.) and prebaked at 100°C for 60 seconds using a hot plate to produce a 40-nm-thick resist film. The resist film was exposed using an Elionix EB lithography system (ELS-F125, accelerating voltage 125 kV), subjected to PEB on a hot plate at the temperature listed in Table 2 for 60 seconds, and developed for 30 seconds using 2-heptanone as the developer to form a pattern. As a result, a negative-tone line-and-space (LS) pattern with a space width of 20 nm and a pitch of 40 nm was obtained. The resulting LS pattern was evaluated for sensitivity, LWR, and limiting resolution according to the following methods. The results are shown in Table 2.

[0066] [Sensitivity evaluation] The LS pattern was observed under an electron microscope to determine the optimum exposure dose Eop (μC / cm) for obtaining an LS pattern with a space width of 20 nm and a pitch of 40 nm. 2 ) was calculated and used as the sensitivity.

[0067] [LWR rating] The LS pattern obtained by irradiating with the optimum exposure dose was measured at 10 points in the longitudinal direction of the space width using a CD-SEM (CG-5000) manufactured by Hitachi High-Tech Corporation, and the three-fold value (3σ) of the standard deviation (σ) was calculated from the results and used as the LWR. The smaller this value, the less roughness and the more uniform the space width pattern obtained.

[0068] [Limiting resolution evaluation] The limiting line width (nm) that can be resolved when forming a pattern by gradually increasing the exposure dose from the optimum exposure dose was determined using a critical dimension SEM (CG-6300) manufactured by Hitachi High-Technologies Corporation, and this was taken as the limiting resolution (nm). The smaller this value, the better the limiting resolution, indicating that finer patterns can be formed.

[0069] [Evaluation of post-exposure storage stability] After exposure at the optimum exposure dose, PEB and development were performed under the conditions described above. Two wafers were developed without post-PEB settling (PPD0h) and developed after 6 hours of PEB settling (PPD6h). The line widths of these wafers were measured using a Hitachi High-Technologies Corporation CD-SEM (CG-6300) to determine the change in line width (CD) (ΔPPD) due to post-exposure settling. The results are shown in Table 2.

[0070] [Table 2]

[0071] The results shown in Table 2 demonstrate that the resist composition of the present invention exhibits excellent LWR and limiting resolution when used in negative pattern formation by organic solvent development using EB lithography. Furthermore, there was little change in CD even after exposure and subsequent storage, demonstrating stability after pattern formation. Furthermore, because the resist composition of the present invention contains a high density of zinc atoms with high EUV light absorption, it is expected to exhibit significantly higher sensitivity in EUV lithography.

[0072] [4] Storage stability evaluation [Examples 3-1 to 3-7, Comparative Example 3-1] Resist compositions R-1 to R-7 and CR-1 were left at room temperature (20±5°C) for a specific period of time, and the occurrence of precipitation was visually confirmed. Those that could be stored for 6 months or more without precipitation were marked with a circle, and those that showed precipitation in less than 6 months were marked with an X. The results are shown in Table 3.

[0073] [Table 3]

[0074] The results shown in Table 3 demonstrate that the resist composition of the present invention has excellent storage stability and is easy to handle.

Claims

1. A resist composition comprising a zinc tetranuclear cluster.

2. 2. The resist composition according to claim 1, wherein the zinc tetranuclear cluster is represented by the following formula (1): 【Chemical 1】 (In the formula, R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each independently a hydrogen atom or a hydrocarbyl group having 1 to 20 carbon atoms which may contain a heteroatom.

3. 3. The resist composition according to claim 2, wherein the zinc tetranuclear cluster is represented by the following formula (2): 【Chemistry 2】 (In the formula, R 11 , R 12 , R 13 , R 14 , R 15 and R 16 are each independently a crosslinkable group-containing group having 1 to 20 carbon atoms.

4. 2. The resist composition according to claim 1, further comprising a carboxylic acid compound.

5. 2. The resist composition according to claim 1, further comprising a photoacid generator.

6. 6. A pattern forming method, comprising: a step of forming a resist film on a substrate using the resist composition according to claim 1; a step of exposing the resist film to high-energy rays; and a step of developing the exposed resist film to form a resist pattern.

7. 7. The pattern forming method according to claim 6, wherein the high-energy beam is an electron beam or extreme ultraviolet light.

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