Pattern forming process and shrink agent

A negative pattern is formed by applying a resist composition onto a substrate, exposing the resist film, and developing the exposed resist film in an organic solvent developer. The process further involves coating the negative pattern with a shrink agent solution of a polymer comprising recurring units capable of forming lactam under the action of acid in a C7-C16 ester or C7-C16 ketone solvent, baking the coating, and removing the excessive shrink agent via organic solvent development for thereby shrinking the size of spaces in the pattern.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2014-223972 filed in Japan on Nov. 4, 2014, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a shrink agent and a pattern forming process comprising forming a resist pattern via resist coating, exposure and development, coating the resist pattern with a shrink agent, baking, and developing the shrink agent for shrinking the size of spaces in the resist pattern.

BACKGROUND ART

While the effort to reduce the pattern rule is in rapid progress to meet the recent demand for higher integration level and operating speed of LSIs, the photolithography is on widespread use. The photolithography has the essential limit of resolution determined by the wavelength of a light source. One micropatterning approach to go beyond the limit of resolution is by combining ArF excimer laser immersion lithography with double patterning. One typical version of double patterning is litho-etch-litho-etch (LELE) process involving forming a pattern via exposure, transferring the pattern to a hard mask on a substrate by etching, effecting second exposure at a half-pitch shifted position, and etching the hard mask. This process has the problem of misalignment between two exposures or overlay error. Another version of double patterning is self-aligned double patterning (SADP) process involving the steps of transferring a resist pattern to a hard mask, growing a film on opposite sides of hard mask features, and leaving sidewalls of film for thereby doubling pattern size. The SADP process needs exposure only once and mitigates the problem of overlay error. To simplify the process, a modified version of the SADP process of forming a silicon oxide film on sidewalls of resist pattern features as developed rather than sidewalls of hard mask features for thereby doubling pattern size is also proposed. Since the SADP process is successful in reducing the pitch of line pattern to half, the pitch can be reduced to ¼ by repeating the SADP process twice.

Not only shrinking of line patterns, but also shrinking of hole patterns is necessary. Unless the hole pattern is shrunk, shrinkage over the entire chip is incomplete. One known method of shrinking a hole pattern is RELACS® method described in JP-A H10-073927. This method intends to reduce the size of a hole pattern by coating a resist pattern as developed with a water-soluble material containing a crosslinker, and baking the coating to form a crosslinked layer on the resist surface for causing the resist pattern to be thickened. JP-A 2008-275995 describes a water-soluble shrink material comprising an amino-containing polymer or polyamine, which bonds to the resist surface via neutralization reaction with carboxyl groups on the resist surface, for thereby thickening the resist film. It is also proposed in Proc. SPIE Vol. 8323 p83230W-1 (2012) to shrink a hole pattern by utilizing the direct self-assembly (DSA) of a block copolymer.

Shrinkage by the RELACS® method has the problem that since a crosslinker becomes active with an acid catalyst within resist, the size of holes is non-uniform after shrinkage if acid diffusion is non-uniform. In the shrink method based on neutralization and bonding of water-soluble amino polymer, the pattern is thickened as direct reflection of irregularities on the resist surface so that dimensional variations of the resist pattern as developed and dimensional variations after shrinkage are identical. The shrink method utilizing the DSA function of a block copolymer has advantages including an increased amount of shrinkage and a minimal dimensional variation after shrinkage, but some problems. Namely, if the DSA is applied to holes of different size, shrinkage cannot be induced for those holes of the size that causes a contradictory assembly of block copolymer. If the DSA is applied to a trench pattern, shape deformation becomes a problem, for example, a plurality of hole patterns are formed.

There is a need for a shrink agent which can shrink a trench pattern without changing the shape of the resist pattern, and improve the dimensional variation and edge roughness (LWR) of the resist pattern after development.

CITATION LIST

SUMMARY OF INVENTION

As discussed above, the method of applying a RELACS® material of crosslink type or neutralizing reaction-mediated bond type onto a resist pattern causes no pattern deformation, but fails to reduce the dimensional variation of the resist pattern. The DSA method can reduce the dimensional variation of a hole pattern as developed, but invites pattern deformation when applied to a trench pattern as developed.

An object of the invention is to provide a shrink agent which when coated onto a resist pattern as developed, can reduce the dimensional variation of the resist pattern, and when applied to a trench pattern, can shrink the trench size without causing pattern deformation; and a pattern forming process using the same.

In one aspect, the invention provides a pattern forming process comprising the steps of applying a resist composition comprising a polymer comprising recurring units having an acid labile group-substituted carboxyl group, an acid generator and an organic solvent, onto a substrate, prebaking to form a resist film; exposing the resist film to high-energy radiation, baking the film; developing the exposed resist film in an organic solvent-based developer to form a negative resist pattern; applying a shrink agent onto the negative resist pattern, baking; and removing the excessive shrink agent with the organic solvent-based developer for thereby shrinking the size of spaces in the pattern. The shrink agent used herein is a solution of a polymer comprising recurring units (a1) having the general formula (1) in a solvent selected from the group consisting of ester solvents of 7 to 16 carbon atoms and ketone solvents of 7 to 16 carbon atoms.

Herein R1is hydrogen or methyl; R2is a straight or branched C2-C8alkylene group; R3is a straight, branched or cyclic C1-C8alkyl group which may contain an ether moiety, ester moiety or halogen, or an acid labile group; X1is phenylene or —C(═O)—O—R4—; R4is a single bond, a straight, branched or cyclic C1-C8alkylene group, or phenylene group.

In a preferred embodiment, the polymer in the resist composition comprises recurring units (a2) having the general formula (2).

Herein R5is hydrogen or methyl, R6is an acid labile group, Z is a single bond or —C(═O)—O—R7—, R7is a straight, branched or cyclic C1-C10alkylene group which may contain ether or ester, or naphthylene group, and 0<a2<1.0.

Typically, the high-energy radiation in the exposure step is i-line of wavelength 364 nm, KrF excimer laser of wavelength 248 nm, ArF excimer laser of wavelength 193 nm, EUV of wavelength 13.5 nm, or EB.

In another aspect, the invention provides a shrink agent comprising a polymer comprising recurring units (a1) having the general formula (1), defined above, and at least one solvent selected from ester solvents of 7 to 16 carbon atoms and ketone solvents of 7 to 16 carbon atoms.

The shrink agent may further comprise at least one of salt compounds having the general formulae (3)-1 and (3)-2:
R8—CO2−M+(3)-1
R9—SO3−M+(3)-2
wherein R8and R9each are a straight, branched or cyclic C1-C20alkyl group, C2-C20alkenyl group or C6-C20aryl group which may contain fluorine, ether, ester, lactone ring, lactam ring, carbonyl, amino or hydroxyl, and M is sulfonium, iodonium or ammonium.

Advantageous Effects of Invention

The process of the invention involves forming a resist film of a photoresist composition comprising a polymer having an acid labile group-substituted carboxyl group and an acid generator, forming a negative tone pattern from the resist film via exposure and organic solvent development, coating the resist pattern with a shrink agent, i.e., a solution of a polymer comprising recurring units capable of forming lactam under the action of acid as represented by formula (1) in an ester solvent of 7 to 16 carbon atoms or ketone solvent of 7 to 16 carbon atoms which does not dissolve the resist pattern, baking, and removing the excessive shrink agent via organic solvent development again. The size of spaces in the resist pattern can be shrunk in a precisely size-controlled manner.

DESCRIPTION OF PREFERRED EMBODIMENTS

The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. “Optional” or “optionally” means that the subsequently described event or circumstances may or may not occur, and that description includes instances where the event or circumstance occurs and instances where it does not. As used herein, the notation (Cn-Cm) means a group containing from n to m carbon atoms per group. As used herein, the term “film” is used interchangeably with “coating” or “layer.”

The abbreviations and acronyms have the following meaning.EB: electron beamMw: weight average molecular weightMn: number average molecular weightMw/Mn: molecular weight distribution or dispersityGPC: gel permeation chromatographyPEB: post-exposure bakePAG: photoacid generatorLWR: line width roughnessLER: line edge roughness

Seeking a shrink material capable of effectively shrinking a resist pattern as developed and a shrink process using the same, the inventors have found the following. A photoresist composition comprising a polymer having an acid labile group-substituted carboxyl group and an acid generator is coated to form a resist film. The resist film is processed via exposure and organic solvent development to form a negative tone resist pattern. Thereafter, the size of spaces in the resist pattern can be shrunk in a precisely size-controlled manner by coating the resist pattern with a shrink agent, i.e., a solution of a polymer comprising recurring units capable of forming lactam under the action of acid as represented by formula (1) in an ester solvent of 7 to 16 carbon atoms or ketone solvent of 7 to 16 carbon atoms, baking, and removing the excessive shrink agent via organic solvent development.

The shrink agent used in the pattern forming process of the invention is a solution of a polymer in a solvent. The polymer is defined as comprising recurring units (a1) capable of forming lactam under the action of acid, represented by the general formula (1).

Herein R1is hydrogen or methyl. R2is a straight or branched C2-C8alkylene group. R3is a straight, branched or cyclic C1-C8alkyl group which may contain an ether moiety, ester moiety or halogen, or an acid labile group. X1is phenylene or —C(═O)—O—R4— wherein R4is a single bond, a straight, branched or cyclic C1-C8alkylene group, or phenylene group.

Under the action of acid, the recurring unit (a1) of formula (1) forms a lactam ring according to the following scheme.

It should be avoided that when the shrink agent solution is applied onto a resist pattern, the resist pattern is dissolved in the solvent of the shrink agent. To this end, the solvent of the shrink agent must be selected from those solvents that do not dissolve the resist film. The solvents that do not dissolve the resist film include ether solvents of 6 to 12 carbon atoms, alcohol solvents of 4 to 10 carbon atoms, hydrocarbon solvents of 6 to 12 carbon atoms, ester solvents of 7 to 16 carbon atoms, ketone solvents of 7 to 16 carbon atoms, and water. Although a number of water-based shrink agents are already proposed as alluded to previously, they are difficult to quickly apply to large-diameter wafers because of the high surface tension of water. A problem arises particularly in the case of a fine hole pattern formed via negative development. When holes are filled with the shrink agent by spin coating, the water solvent having a high surface tension prevents the shrink agent from burying in the holes to the bottom. In contrast, when a shrink agent dissolved in an organic solvent having a lower surface tension than water is applied, the ability to fill or bury to the hole bottom is improved. Also the organic solvent used in the shrink agent must dissolve the base polymer of the shrink agent. As the solvent capable of dissolving a polymer comprising recurring units having formula (1), ester solvents of 7 to 16 carbon atoms and ketone solvents of 7 to 16 carbon atoms must be selected among the aforementioned organic solvents.

The recurring unit (a1) is derived from a monomer Mal having the following formula.

Examples of monomer Mal are shown below. Herein R1and R3are as defined above.

In addition to the recurring units (a1) of formula (1), the polymer for the shrink agent may further comprise recurring units of at least one type selected from recurring units (a3) and (a4) having a substituted carboxyl and hydroxyl group, represented by the general formula (4).

Herein R9and R11each are hydrogen or methyl. R10and R13each are an acid labile group. X2is a single bond, a phenylene or naphthylene group, or —C(═O)—O—R14—, wherein R14is a straight, branched or cyclic C1-C10alkylene group which may contain ether, ester, lactone ring or hydroxyl, or a phenylene or naphthylene group. X3is a single bond, a phenylene or naphthylene group which may contain nitro, cyano or halogen, or —C(═O)—O—R15—, —C(═O)—NH—R15—, —O—R15—, or —S—R15—, wherein R15is a straight, branched or cyclic C1-C10alkylene group which may contain ether, ester, lactone ring or hydroxyl, or a phenylene or naphthylene group which may contain a straight, branched or cyclic C1-C6alkyl, alkoxy, acyl, acyloxy, C2-C6alkenyl, alkoxycarbonyl, C6-C10aryl, nitro, cyano, or halogen. R12is a single bond, a di to penta-valent, straight, branched or cyclic C1-C16aliphatic hydrocarbon group, or phenylene group, which may contain an ether or ester moiety. The subscripts a3 and a4 are numbers in the range: 0≦a3<1.0, 0≦a4<1.0, 0≦a3+a4<1.0, preferably 0<a3+a4<1.0, and n is 1 to 4.

In addition to the recurring units (a1) of formula (1), the polymer may further comprise recurring units (a5) and/or (a6) adapted to cyclize to form lactone under the action of acid, represented by the general formula (5).

Herein R16and R22each are hydrogen or methyl. R17and R18are each independently hydrogen, fluorine, or a straight, branched or cyclic, C1-C8monovalent hydrocarbon group. R19, R23and R25are each independently hydrogen or a straight, branched or cyclic, C1-C20monovalent hydrocarbon group in which any constituent —CH2— moiety may be replaced by —O— or —C(═O)—, or whose hydrogen may be replaced by halogen. R20and R21are each independently hydrogen or a straight, branched or cyclic, C1-C8monovalent hydrocarbon group, or R20and R21may bond together to form a C3-C17non-aromatic ring with the carbon atom to which they are attached. R24is an acid labile group. X4and X5are each independently a straight, branched or cyclic, C1-C20divalent hydrocarbon group in which any constituent —CH2— moiety may be replaced by —O— or —C(═O)—. The subscripts k1and k2each are 0 or 1, a5 and a6 are numbers in the range: 0≦a5<1.0, 0≦a6<1.0, and 0≦a5+a6<1.0, preferably 0<a5+a6<1.0.

In addition to the recurring units, the polymer may further comprise recurring units (b) having a hydroxyl, carboxyl, lactone ring, lactam ring, sultone ring, sulfone, sulfonic acid ester, sulfonamide, carboxylic acid amide, nitro, cyano, thienyl, furyl, pyrrole, acid anhydride, imide, —NH—(C═O)—O—, —S—(C═O)—O, or —ON(═O2)—. Examples of the monomer from which recurring units (b) are derived are shown below.

In the polymer comprising the aforementioned recurring units (a1), (a3), (a4), (a5) and (b), additional recurring units may be copolymerized. Exemplary are recurring units (c) having a non-leaving hydrocarbon group as described in JP-A 2008-281980. Suitable non-leaving hydrocarbon groups include those described in JP-A 2008-281980, and indenes, acenaphthylenes, and norbornadienes. By copolymerizing recurring units (c) having a non-leaving hydrocarbon group, the polymer is improved in solubility in the C7-C16ester and C7-C16ketone solvents, and also improved in dry etching resistance when the substrate is etched through the pattern after shrinkage.

Further, recurring units (d) having an oxirane or oxetane ring may be copolymerized. Once recurring units (d) having an oxirane or oxetane ring are copolymerized, crosslinking can take place at the interface between the shrink agent and the resist film, leading to an increase of shrinkage. Examples of the monomers from which recurring units (d) having an oxirane or oxetane ring are derived are shown below. Note that R41is hydrogen or methyl.

The acid labile group R3in recurring unit (a1), the acid labile groups R10and R13substituting on the carboxyl and hydroxyl groups in formula (4), and the acid labile group R24in formula (5) in the polymer for the shrink agent, and the acid labile group R6substituting on the carboxyl group in the base polymer for the photoresist (to be described later) may be selected from a variety of such groups while they may be the same or different. Preferred acid labile groups include groups of formula (AL-10), acetal groups of formula (AL-11), tertiary alkyl groups of formula (AL-12), and oxoalkyl groups of 4 to 20 carbon atoms.

In formulae (AL-10) and (AL-11), R51and R54each are a monovalent hydrocarbon group, typically a straight, branched or cyclic alkyl group of 1 to 40 carbon atoms, more specifically 1 to 20 carbon atoms, which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. The subscript “a5” is an integer of 0 to 10, preferably 1 to 5. R52and R53each are hydrogen or a monovalent hydrocarbon group, typically a straight, branched or cyclic C1-C20alkyl group, which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. Alternatively, a pair of R52and R53, R52and R54, or R53and R54, taken together, may form a ring, specifically aliphatic ring, with the carbon atom or the carbon and oxygen atoms to which they are attached, the ring having 3 to 20 carbon atoms, especially 4 to 16 carbon atoms.

In formula (AL-12), R55, R56and R57each are a monovalent hydrocarbon group, typically a straight, branched or cyclic C1-C20alkyl group, which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. Alternatively, a pair of R55and R56, R55and R57, or R56and R57, taken together, may form a ring, specifically aliphatic ring, with the carbon atom to which they are attached, the ring having 3 to 20 carbon atoms, especially 4 to 16 carbon atoms.

Illustrative examples of the groups of formula (AL-10) include tert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl, tert-amyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl, 2-tetrahydropyranyloxycarbonylmethyl and 2-tetrahydrofuranyloxycarbonylmethyl as well as substituent groups of the following formulae (AL-10)-1 to (AL-10)-10.

In formulae (AL-10)-1 to (AL-10)-10, R58is independently a straight, branched or cyclic C1-C8alkyl group, C6-C20aryl group or C7-C20aralkyl group; R59is hydrogen or a straight, branched or cyclic C1-C20alkyl group; RHis a C6-C20aryl group or C7-C20aralkyl group; and “a5” is an integer of 0 to 10 as defined above.

Illustrative examples of the acetal group of formula (AL-11) include those of the following formulae (AL-11)-1 to (AL-11)-112.

The polymer may be crosslinked within the molecule or between molecules with acid labile groups of formula (AL-11a) or (AL-11b).

Herein R61and R62each are hydrogen or a straight, branched or cyclic C1-C8alkyl group, or R61and R62, taken together, may form a ring with the carbon atom to which they are attached, and R61and R62are straight or branched C1-C8alkylene groups when they form a ring. R63is a straight, branched or cyclic C1-C10alkylene group. Each of b5 and d5 is 0 or an integer of 1 to 10, preferably 0 or an integer of 1 to 5, and c5 is an integer of 1 to 7. “A” is a (c5+1)-valent aliphatic or alicyclic saturated hydrocarbon group, aromatic hydrocarbon group or heterocyclic group having 1 to 50 carbon atoms, which may be separated by a heteroatom such as oxygen, sulfur or nitrogen or in which some of the hydrogen atoms attached to carbon atoms may be substituted by hydroxyl, carboxyl, carbonyl radicals or fluorine atoms. “B” is —CO—O—, —NHCO—O— or —NHCONH—.

Preferably, “A” is selected from divalent to tetravalent, straight, branched or cyclic C1-C20alkylene, alkanetriyl and alkanetetrayl groups, and C6-C30arylene groups, which may be separated by a heteroatom such as oxygen, sulfur or nitrogen or in which some of the hydrogen atoms attached to carbon atoms may be substituted by hydroxyl, carboxyl, acyl radicals or halogen atoms. The subscript c5 is preferably an integer of 1 to 3.

The crosslinking acetal groups of formulae (AL-11a) and (AL-11b) are exemplified by the following formulae (AL-11)-113 through (AL-11)-120.

Illustrative examples of the tertiary alkyl of formula (AL-12) include tert-butyl, triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl, 1-ethylcyclopentyl, and tert-amyl groups as well as those of (AL-12)-1 to (AL-12)-16.

Herein R64is independently a straight, branched or cyclic C1-C8alkyl, C6-C20aryl or C7-C20aralkyl group, or two R64may bond together to form a ring. R65and R67each are hydrogen, methyl or ethyl. R66is a C6-C20aryl or C7-C20aralkyl group.

Also included are acid labile groups of the formula (AL-12)-17.

Herein R64is as defined above, R68is a single bond or a straight, branched or cyclic C1-C20alkylene group or arylene group which may contain a heteroatom such as oxygen, sulfur or nitrogen, and b6 is an integer of 0 to 3. With acid labile groups of formula (AL-12)-17 containing R68representative of a di- or poly-valent alkylene or arylene group, the polymer may be crosslinked within the molecule or between molecules. It is noted that formula (AL-12)-17 is applicable to all the foregoing acid labile groups.

The groups represented by R64, R65, R66and R67may contain a heteroatom such as oxygen, nitrogen or sulfur. Such groups are exemplified by those of the following formulae (AL-13)-1 to (AL-13)-7.

Of the acid labile groups of formula (AL-12), groups of exo-form structure having the following formula (AL-12)-19 are preferred.

Herein R69is a straight, branched or cyclic C1-C8alkyl group or optionally substituted C6-C20aryl group. R70to R75, R78, and R79are each independently hydrogen or a monovalent C1-C15hydrocarbon group, typically alkyl, which may contain a heteroatom, R76and R77are hydrogen; or a pair of R70and R71, R72and R74, R72and R75, R73and R75, R73and R79, R74and R78, R76and R77, or R77and R78may bond together to form a ring, typically aliphatic ring, with the carbon atom to which they are attached, and in this case, the ring-forming participant is a divalent C1-C15hydrocarbon group, typically alkylene, which may contain a heteroatom. Also, a pair of R70and R79, R76and R79, or R72and R74which are attached to vicinal carbon atoms may bond together directly to form a double bond. The formula also represents an enantiomer.

The ester form monomers from which recurring units having an exo-form structure represented by the formula (AL-12)-19 shown below are derived are described in U.S. Pat. No. 6,448,420 (JP-A 2000-327633).

R is hydrogen or methyl. Illustrative non-limiting examples of suitable monomers are given below.

Also included in the acid labile groups of formula (AL-12) are acid labile groups having furandiyl, tetrahydrofurandiyl or oxanorbornanediyl as represented by the following formula (AL-12)-20.

Herein, R80and R81are each independently a monovalent hydrocarbon group, typically a straight, branched or cyclic C1-C10alkyl group. R80and R81, taken together, may form an aliphatic hydrocarbon ring of 3 to 20 carbon atoms with the carbon atom to which they are attached. R82is a divalent group selected from furandiyl, tetrahydrofurandiyl and oxanorbornanediyl. R83is hydrogen or a monovalent hydrocarbon group, typically a straight, branched or cyclic C1-C10alkyl group, which may contain a heteroatom.

Recurring units substituted with an acid labile group having furandiyl, tetrahydrofurandiyl or oxanorbornanediyl as represented by the formula:

(wherein R, R80to R83are as defined above) are derived from monomers, examples of which are shown below. Note that Me is methyl and Ac is acetyl.

Of the acid labile groups of tertiary alkyl form having formula (AL-12), those acid labile groups having a branched alkyl directly attached to the ring offer high solubility in organic solvents. Such acid labile groups are exemplified below. In the following formula, the line segment protruding out of the bracket denotes a valence bond.

On the other hand, the base resin in the resist composition used to form a resist pattern is a polymer comprising recurring units (a2) having an acid labile group-substituted carboxyl group, preferably represented by the general formula (2).

Herein R5is hydrogen or methyl. R6is an acid labile group. Z is a single bond or —C(═O)—O—R7— wherein R7is a straight, branched or cyclic C1-C10alkylene group which may contain an ether or ester moiety, or naphthylene group, and a2 is a number in the range: 0<a2<1.0.

In the polymer comprising recurring units (a2) for use in the resist composition, recurring units (b) as described above may be copolymerized for improving the insolubility of the exposed region in organic solvent developer, improving adhesion to the substrate, and preventing pattern collapse. Further, there may be copolymerized recurring units having an adhesive group selected from among hydroxyl, lactone ring, ether, ester, carbonyl and cyano groups as described in JP-A 2012-037867, paragraphs [0076]-[0084], an indene, acenaphthylene, chromone, coumarin, and norbornadiene as described in paragraph [0085], a styrene, vinylnaphthalene, vinylanthracene, vinylpyrene, and methyleneindane as described in paragraph [0088], and an acid generator in the form of an onium salt having polymerizable olefin as described in paragraphs [0089]-[0091].

The following discussion applies to both the polymer serving as the shrink agent and the polymer serving as the base resin in the resist composition, both used in the patterning process. The polymer should preferably have a weight average molecular weight (Mw) in the range of 1,000 to 500,000, and more preferably 2,000 to 100,000, as measured by GPC versus polystyrene standards. If Mw is too low, in the case of shrink agent, the amount of shrinkage may become excessive or even uncontrollable due to an extended acid diffusion distance, and in the case of resist composition, the diffusion distance of acid generated by PAG may be extended to invite a drop of resolution. If Mw is too high, in the case of shrink agent, the solubility of the polymer in stripper solvent may be reduced, leaving scum in spaces at the end of removal step, and in the case of resist composition, a footing phenomenon is likely to occur after pattern formation.

If a polymer has a wide molecular weight distribution or dispersity (Mw/Mn), which indicates the presence of lower and higher molecular weight polymer fractions, there is a possibility that foreign matter is left on the pattern or the pattern profile is degraded. The influences of molecular weight and dispersity become stronger as the pattern rule becomes finer. Therefore, the multi-component copolymer should preferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in order to provide a resist composition suitable for micropatterning to a small feature size.

It is understood that a blend of two or more polymers which differ in compositional ratio, molecular weight or dispersity is acceptable.

The polymers used herein may be synthesized by any desired method, for example, by dissolving one or more monomers in an organic solvent, adding a radical initiator thereto, and effecting heat polymerization. The monomers used herein include monomers corresponding to recurring units (a1), (b) and other units in the case of shrink agent polymer, and monomers corresponding to acid labile group-bearing recurring units (a2), adhesive group-bearing recurring units (b) and the like in the case of resist polymer, and other unsaturated bond-bearing monomers. Examples of the organic solvent which can be used for polymerization include toluene, benzene, tetrahydrofuran, diethyl ether and dioxane. Examples of the polymerization initiator used herein include 2,2′-azobisisobutyronitrile (AIBN), 2,2′-azobis(2,4-dimethyl-valeronitrile), dimethyl 2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide. Preferably the system is heated at 50 to 80° C. for polymerization to take place. The reaction time is 2 to 100 hours, preferably 5 to 20 hours. The acid labile group that has been incorporated in the monomer may be kept as such, or the acid labile group may be once removed with an acid catalyst and the resulting polymer be protected or partially protected. In the polymer serving as the shrink agent, recurring units (a1) and (b) may be arranged randomly or blockwise.

The shrink agent used in the pattern forming process further contains an organic solvent and optionally a salt, basic compound and surfactant.

In the shrink agent solution, the solvent is preferably used in an amount of 100 to 100,000 parts, more preferably 200 to 50,000 parts by weight per 100 parts by weight of the polymer.

To the shrink agent, a salt and basic compound may be added if desired. The salt that can be added is typically selected from sulfonium salts and iodonium salts which are typically added to resist compositions, and ammonium salts. The basic compound that can be added may be selected from those basic compounds which are typically added to resist compositions, for example, primary, secondary and tertiary aliphatic amines, mixed amines, aromatic amines, heterocyclic amines, nitrogen-containing compounds having carboxyl group, nitrogen-containing compounds having sulfonyl group, nitrogen-containing compounds having hydroxyl group, nitrogen-containing compounds having hydroxyphenyl group, alcoholic nitrogen-containing compounds, amide derivatives, and imide derivatives. The addition of the salt or basic compound is effective for suppressing excessive diffusion of acid from within the resist film and for controlling the amount of shrinkage. The surfactant that can be added may be selected from those surfactants which are typically added to resist compositions.

As the salt, salt compounds having the general formulae (3)-1 and (3)-2 are preferred.
R8—CO2−M+(3)-1
R9—SO3−M+(3)-2
Herein R8and R9each are a straight, branched or cyclic C1-C20alkyl group, C2-C20alkenyl group or C6-C20aryl group which may contain fluorine, ether moiety, ester moiety, lactone ring, lactam ring, carbonyl moiety, amino moiety or hydroxyl moiety, and M is sulfonium, iodonium or ammonium.

Examples of the anion: R8—CO2−are shown below.

Examples of the anion: R9—SO3−are shown below.

Of the salt compounds of formula (3)-1, sulfonium, iodonium and ammonium salts of carboxylic acid represented by formulae (P1a-1) to (P1a-3) are preferred. Of the salt compounds of formula (3)-2, sulfonium, iodonium and ammonium salts of sulfonic acid represented by formulae (P1b-1) to (P1b-3) are preferred. Acid diffusion may be effectively controlled by adding these salts.

Herein R101a, R101b, R101cand R101dare each independently a straight, branched or cyclic C1-C12alkyl, alkenyl, oxoalkyl or oxoalkenyl, C6-C20aryl, or C7-C12aralkyl or aryloxoalkyl group, in which some or all hydrogen atoms may be replaced by alkoxy or other groups, R101band R101cmay bond together to form a ring which may contain an ether, ester, sultone or amino moiety, each of R101band R101cis C1-C10alkylene or arylene when they form a ring. R8is as defined above.

In the shrink agent, preferably the salt is used in an amount of 0 to 50 parts by weight, the basic compound is used in an amount of 0 to 30 parts by weight, and the surfactant is used in an amount of 0 to 10 parts, more preferably 0 to 5 parts by weight, all per 100 parts by weight of the polymer. When added, each additive is preferably used in an amount of at least 0.1 part by weight.

The resist composition comprises the polymer as base resin, an organic solvent, and an acid generator (i.e., compound capable of generating an acid in response to high-energy radiation), and optionally, a dissolution regulator, basic compound, surfactant, acetylene alcohol, and other components.

Specifically, the resist composition contains an acid generator such that it may function as a chemically amplified resist composition. The acid generator is typically a compound capable of generating an acid in response to actinic light or radiation, known as photoacid generator (PAG). An appropriate amount of the PAG used is 0.5 to 30 parts, more preferably 1 to 20 parts by weight per 100 parts by weight of the base resin. The PAG is any compound capable of generating an acid upon exposure to high-energy radiation. Suitable PAGs include sulfonium salts, iodonium salts, sulfonyldiazomethane, N-sulfonyloxyimide, and oxime-O-sulfonate acid generators. The acid generators may be used alone or in admixture of two or more. Exemplary of the acid generated by PAG are sulfonic acids, imidic acids and methide acids. Of these, sulfonic acids which are fluorinated at α-position are most commonly used. Where the acid labile group is an acetal group susceptible to deprotection, fluorination at α-position is not always necessary. Where the base polymer has recurring units of acid generator copolymerized therein, the acid generator need not be separately added.

Examples of the organic solvent used herein are described in JP-A 2008-111103, paragraphs [0144] to [0145] (U.S. Pat. No. 7,537,880). Specifically, exemplary solvents include ketones such as cyclohexanone and methyl-2-n-amyl ketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol; 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; esters such as propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate, tert-butyl propionate, and propylene glycol mono-tert-butyl ether acetate; and lactones such as γ-butyrolactone, and mixtures thereof. Where an acid labile group of acetal form is used, a high-boiling alcohol solvent such as diethylene glycol, propylene glycol, glycerol, 1,4-butanediol or 1,3-butanediol may be added for accelerating deprotection reaction of acetal.

Exemplary basic compounds include primary, secondary and tertiary amine compounds, specifically amine compounds having a hydroxyl, ether, ester, lactone, cyano or sulfonate group, as described in JP-A 2008-111103, paragraphs [0146] to [0164], and compounds having a carbamate group, as described in JP 3790649. Also, onium salts such as sulfonium salts, iodonium salts and ammonium salts of sulfonic acids which are not fluorinated at α-position as described in US 2008153030 (JP-A 2008-158339) and similar onium salts of carboxylic acid as described in JP 3991462 and JP 4226807 may be used as the quencher. They may also be added to the shrink agent.

Where the acid labile group is an acetal group which is very sensitive to acid, the acid for eliminating the protective group need not necessarily be a sulfonic acid which is fluorinated at α-position, imidic acid or methide acid. Even with a sulfonic acid which is not fluorinated at α-position, deprotection reaction may take place in some cases. Since an onium salt of sulfonic acid cannot be used as the quencher in this event, an onium salt of imidic acid is preferably used alone.

Exemplary surfactants are described in JP-A 2008-111103, paragraphs [0165]-[0166]. Exemplary dissolution regulators are described in JP-A 2008-122932 (US 2008090172), paragraphs [0155]-[0178], and exemplary acetylene alcohols in paragraphs [0179]-[0182].

Also a polymeric additive may be added for improving the water repellency on surface of a resist film as spin coated. This additive may be used in the topcoatless immersion lithography. These additives have a specific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue and are described in JP-A 2007-297590 and JP-A 2008-111103. The water repellency improver to be added to the resist composition should be soluble in the organic solvent as the developer. The water repellency improver of specific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue is well soluble in the developer. A polymer having an amino group or amine salt copolymerized as recurring units may serve as the water repellent additive and is effective for preventing evaporation of acid during PEB and avoiding any hole pattern opening failure after development. An appropriate amount of the water repellency improver is 0.1 to 20 parts, preferably 0.5 to 10 parts by weight per 100 parts by weight of the base resin.

Notably, an appropriate amount of the organic solvent is 100 to 10,000 parts, preferably 300 to 8,000 parts by weight, and an appropriate amount of the basic compound is 0.0001 to 30 parts, preferably 0.001 to 20 parts by weight, per 100 parts by weight of the base resin. The dissolution regulator, surfactant and acetylene alcohol may be used in any suitable amounts, depending on their purpose of addition.

Referring toFIGS. 1 and 2, the pattern shrinking process of the invention is described. First, as shown inFIG. 1A, a chemically amplified resist composition is applied onto a processable substrate20on a substrate10to form a photoresist film30thereon. If necessary, a hard mask layer (not shown) may intervene between the resist film30and the processable substrate20. By standard techniques, the resist film30is subjected to exposure (FIG. 1B), PEB, and organic solvent development to form a negative resist pattern30a(FIG. 1C). A shrink agent40is applied onto the negative resist pattern30ato cover the pattern as shown inFIG. 2D. The shrink agent coating is baked, during which the heat functions to evaporate off the solvent and to cause the acid to diffuse from the resist pattern30into the shrink agent coating40. With the acid, the polymer in the shrink agent coating undergoes deprotection reaction. Thereafter, a solvent is applied to remove the excessive shrink agent40, leaving a shrink agent film40aover the resist pattern30a. This means that the resist pattern30ais thickened at50, that is, the width of spaces in the resist pattern is shrunk as shown inFIG. 2E. Using the shrunk pattern50as a mask, the processable substrate20is dry etched as shown inFIG. 2F.

The substrate10used herein is generally a silicon substrate. The processable substrate (or target film)20used herein includes SiO2, SiN, SiON, SiOC, p-Si, α-Si, TiN, WSi, BPSG, SOG, Cr, CrO, CrON, MoSi, low dielectric film, and etch stopper film. The hard mask may be of SiO2, SiN, SiON or p-Si. Sometimes, an undercoat in the form of carbon film or a silicon-containing intermediate film may be laid instead of the hard mask, and an organic antireflective coating may be interposed between the hard mask and the resist film.

While a resist film (30) of a chemically amplified resist composition is formed on a processable substrate (20) on a substrate (10) directly or via an intermediate intervening layer as mentioned above, the resist film preferably has a thickness of 10 to 1,000 nm and more preferably 20 to 500 nm. Prior to exposure, the resist film is heated or prebaked, preferably at a temperature of 50 to 180° C., especially 60 to 150° C. for a time of 10 to 300 seconds, especially 15 to 200 seconds.

Next the resist film is exposed to high-energy radiation having a wavelength of up to 400 nm, especially 140 to 250 nm. The high-energy radiation is typically i-line of wavelength 364 nm, KrF excimer laser of wavelength 248 nm, ArF excimer laser of wavelength 193 nm, EUV of wavelength 13.5 nm, or EB. The ArF 193-nm lithography is most preferred. The exposure may be done either in a dry atmosphere such as air or nitrogen stream or by immersion lithography in water. The ArF immersion lithography uses deionized water or liquids having a refractive index of at least 1 and highly transparent to the exposure wavelength such as alkanes as the immersion solvent. In the immersion lithography, the prebaked resist film is exposed to light through a projection lens, with pure water or another liquid introduced between the resist film and the projection lens. Since this allows lenses to be designed to a NA of 1.0 or higher, formation of finer feature size patterns is possible. The immersion lithography is important for the ArF lithography to survive to the 45-nm node. In the case of immersion lithography, deionized water rinsing (or post-soaking) may be carried out after exposure for removing water droplets left on the resist film, or a protective film may be applied onto the resist film after pre-baking for preventing any leach-out from the resist film and improving water slip on the film surface. The resist protective film used in the immersion lithography is preferably formed from a solution of a polymer having 1,1,1,3,3,3-hexafluoro-2-propanol residues which is insoluble in water, but soluble in an alkaline developer liquid, in a solvent selected from alcohols of 4 to 10 carbon atoms, ethers of 8 to 12 carbon atoms, and mixtures thereof. After formation of the photoresist film, deionized water rinsing (or post-soaking) may be carried out for extracting the acid generator and the like from the film surface or washing away particles, or after exposure, rinsing (or post-soaking) may be carried out for removing water droplets left on the resist film.

Exposure is preferably performed in an exposure dose of about 1 to 200 mJ/cm2, more preferably about 10 to 100 mJ/cm2. This is followed by baking (PEB) on a hot plate at 50 to 150° C. for 1 to 5 minutes, preferably at 60 to 120° C. for 1 to 3 minutes.

At the end of development, the resist film may be rinsed. As the rinsing liquid, a solvent which is miscible with the developer and does not dissolve the resist film is preferred. Suitable solvents include alcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12 carbon atoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, and aromatic solvents. Specifically, suitable alkanes of 6 to 12 carbon atoms include hexane, heptane, octane, nonane, decane, undecane, dodecane, methylcyclopentane, dimethylcyclopentane, cyclohexane, methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, and cyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene, heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene, cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atoms include hexyne, heptyne, and octyne. Suitable alcohols of 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-amyl alcohol, neopentyl alcohol, 2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol, cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 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. Suitable ether compounds of 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-amyl ether, and di-n-hexyl ether. Suitable aromatic solvents include toluene, xylene, ethylbenzene, isopropylbenzene, tert-butylbenzene, and mesitylene. The solvents may be used alone or in admixture. After the rinse liquid is applied, the substrate may be dried by spin drying and bake. However, rinsing is not essential. As long as the step of spin drying the substrate after the developer is applied thereto is included, the rinsing step may be omitted.

Following the development, the shrink agent of the invention is applied onto the resist pattern to form a shrink agent coating, preferably having a thickness of 1 to 100 nm, more preferably 1.5 to 50 nm. The shrink agent coating is baked at a temperature of 40 to 180° C. for 5 to 300 seconds. Bake functions to evaporate off the solvent and to induce acid diffusion from the resist film to the shrink agent and deprotection reaction to generate carboxyl and/or hydroxyl groups in the shrink agent coating, for thereby rendering the shrink agent coating insoluble in the organic solvent developer due to a polarity change by the generated lactam ring.

Finally, the excessive shrink agent is removed, preferably using the organic solvent developer. This means that development of the resist film and removal of the shrink agent can be performed with an identical organic solvent. The nozzle needed is only one.

EXAMPLE

Examples of the invention are given below by way of illustration and not by way of limitation. The abbreviation “pbw” is parts by weight, and PGMEA is propylene glycol monomethyl ether acetate. For all polymers, Mw and Mn are determined by GPC versus polystyrene standards.

Synthesis Example

Polymers (for use in shrink agent and resist composition) were synthesized by combining suitable monomers in tetrahydrofuran solvent, effecting copolymerization reaction, crystallizing from methanol, repeatedly washing with hexane, isolation and drying. There were obtained random copolymers, designated Polymers 1 to 8, Comparative Polymers 1, 2, Resist Polymer 1, and Water-repellent Polymer 1. The polymers were analyzed for composition by1H-NMR spectroscopy and for Mw and Mw/Mn by GPC. The polymers are identified below with their analytical data.

Examples 1 to 22 and Comparative Examples 1 to 4

A shrink agent solution was prepared by mixing the polymer synthesized above (Polymers 1 to 8 or Comparative Polymers 1, 2), additive (e.g., sulfonium salt), and solvent in accordance with the formulation of Tables 1 and 2, and filtering through a Teflon® filter having a pore size of 0.2 μm. Components shown in Tables 1 and 2 are identified below.

Acid Generator: PAG1 of the Following Structural Formula

A resist composition in solution form was prepared by dissolving a polymer (Resist Polymer 1), acid generator, quencher, and water-repellent polymer in a solvent in accordance with the formulation of Table 3, and filtering through a filter with a pore size of 0.2 μm. The solvent contained 100 ppm of surfactant FC-4430 (3M-Sumitomo Co., Ltd.).

On a silicon wafer, a spin-on carbon film ODL-102 (Shin-Etsu Chemical Co., Ltd.) was deposited to a thickness of 200 nm and a silicon-containing spin-on hard mask SHB-A940 was deposited thereon to a thickness of 35 nm. On this substrate for trilayer process, the resist composition in Table 3 was spin coated, then baked on a hot plate at 100° C. for 60 seconds to form a resist film of 100 nm thick. Using an ArF excimer laser immersion lithography scanner NSR-610C (Nikon Corp., NA 1.30, σ 0.98/0.78, dipole opening 20 deg., azimuthally polarized illumination), the resist film was exposed through a 6% halftone phase shift mask while varying the exposure dose. After the exposure, the resist film was baked (PEB) at 90° C. for 60 seconds and puddle developed in n-butyl acetate for 30 seconds to form a trench pattern having a space width of 45 nm and a pitch of 100 nm.

The shrink agent shown in Tables 1 and 2 was applied onto the resist pattern after development to cover the pattern. The shrink agent coating was baked at the temperature shown in Tables 4 and 5 for 60 seconds. This was followed by puddle development in n-butyl acetate for 20 seconds to remove the excessive shrink agent. Both after development and after shrink treatment, the pattern was observed under a CD-SEM (CG-4000 by Hitachi, Ltd.) to measure the size of trenches at a pitch of 100 nm and edge roughness. The results are shown in Tables 4 and 5.

Japanese Patent Application No. 2014-223972 is incorporated herein by reference.