RESIST COMPOSITION AND PATTERN FORMING PROCESS

Abstract

A resist composition is provided that comprises a hypervalent iodine compound having the formula (1), a carboxy group-containing polymer, and a solvent. In formula (1), n is an integer of 0 to 5, R.sup.1 and R.sup.2 are each independently halogen or a C.sub.1-C.sub.10 hydrocarbyl group which may contain a heteroatom, R.sup.1 and R.sup.2 may bond together to form a ring with the carbon atoms to which they are attached and the intervenient atoms. R.sup.3 is halogen or a C.sub.1-C.sub.40 hydrocarbyl group which may contain a heteroatom.

##STR00001##

Claims

1. A resist composition comprising a hypervalent iodine compound having the formula (1), a carboxy group-containing polymer, and a solvent: ##STR00055## wherein n is an integer of 0 to 5, R.sup.1 and R.sup.2 are each independently halogen or a C.sub.1-C.sub.10 hydrocarbyl group which may contain a heteroatom, R.sup.1 and R.sup.2 may bond together to form a ring with the carbon atoms to which they are attached and the intervenient atoms, and R.sup.3 is halogen or a C.sub.1-C.sub.40 hydrocarbyl group which may contain a heteroatom.

2. The resist composition of claim 1 wherein the carboxy group-containing polymer comprises a recurring unit having the formula (2): ##STR00056## wherein R.sup.A is a hydrogen atom, fluorine atom, methyl group, or trifluoromethyl group, X.sup.A is a single bond, phenylene group, naphthylene group, or *C(?O)OX.sup.A1 wherein X.sup.A1 is a C.sub.1-C.sub.10 saturated hydrocarbylene group, phenylene group, or naphthylene group, the C.sub.1-C.sub.10 saturated hydrocarbylene group may contain a hydroxy group, ether bond, ester bond, or lactone ring, and * designates a valence bond to a carbon atom in a main chain.

3. A pattern forming process comprising the steps of applying the resist composition of claim 1 onto a substrate to form a resist film thereon, exposing the resist film to an electron beam or an extreme ultraviolet radiation, and developing the exposed resist film in a developer.

4. The pattern forming process of claim 3 wherein the developer is an organic solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

Resist Composition

[0028] One embodiment of the invention is a resist composition based on a predetermined hypervalent iodine compound and a carboxy group-containing polymer.

Hypervalent Iodine Compound

[0029] The hypervalent iodine compound is a three-coordinate hypervalent iodine compound having the formula (1).

##STR00004##

[0030] In the formula (1), n is an integer of 0 to 5.

[0031] In the formula (1), R.sup.1 and R.sup.2 are each independently halogen or a C.sub.1-C.sub.10 hydrocarbyl group which may contain a heteroatom. R.sup.1 and R.sup.2 may bond together to form a ring with the carbon atoms to which they are attached and the intervenient atoms. Examples of the halogen include fluorine, chlorine, bromine, and iodine. The C.sub.1-C.sub.10 hydrocarbyl group may be saturated or unsaturated, and straight, branched, or cyclic. Examples thereof include C.sub.1-C.sub.10 alkyl groups 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; C.sub.3-C.sub.10 cyclic saturated hydrocarbyl groups such as cyclopentyl, cyclohexyl, cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl, norbornyl, tricyclo[5.2.1.0.sup.2,6]decanyl, and adamantyl; C.sub.2-C.sub.10 alkenyl groups such as vinyl and allyl; C.sub.6-C.sub.10 aryl groups such as phenyl and naphthyl; and combinations thereof. Also included are hydrocarbyl groups in which some or all of the hydrogen atoms are substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen, or halogen, and some constituent CH.sub.2 is replaced by a moiety containing a heteroatom such as oxygen, sulfur, or nitrogen, so that the group may contain hydroxy, cyano, halogen, carbonyl, ether bond, thioether bond, ester bond, sulfonic ester bond, carbonate bond, carbamate bond, lactone ring, sultone ring, or carboxylic anhydride (C(?O)OC(?O)). R.sup.1 and R.sup.2 are preferably C.sub.1-C.sub.4 hydrocarbyl groups.

[0032] In the formula (1), R.sup.3 is halogen or a C.sub.1-C.sub.40 hydrocarbyl group which may contain a heteroatom. When n is an integer of 2 to 5, a plurality of R.sup.3 may be the same or different. Examples of the halogen include fluorine, chlorine, bromine, and iodine. The C.sub.1-C.sub.40 hydrocarbyl group may be saturated or unsaturated, and straight, branched, or cyclic. Examples thereof include C.sub.1-C.sub.40 alkyl groups 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; C.sub.3-C.sub.40 cyclic saturated hydrocarbyl groups such as cyclopentyl, cyclohexyl, cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl, norbornyl, tricyclo[5.2.1.0.sup.2,6]decanyl, adamantyl, and adamantylmethyl; and C.sub.6-C.sub.40 aryl groups such as phenyl, naphthyl, and anthracenyl. Also included are hydrocarbyl groups in which some or all of the hydrogen atoms are substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen, or halogen, and some constituent CH.sub.2 is replaced by a moiety containing a heteroatom such as oxygen, sulfur, or nitrogen, so that the group may contain hydroxy, cyano, halogen, carbonyl, ether bond, thioether bond, ester bond, sulfonic ester bond, carbonate bond, carbamate bond, lactone ring, sultone ring, or carboxylic anhydride (C(?O)OC(?O)).

[0033] Examples of the hypervalent iodine compound having the formula (1) are shown below, but not limited thereto.

##STR00005## ##STR00006## ##STR00007## ##STR00008## ##STR00009## ##STR00010## ##STR00011## ##STR00012## ##STR00013## ##STR00014## ##STR00015## ##STR00016## ##STR00017## ##STR00018## ##STR00019##

Carboxy Group-Containing Polymer

[0034] The carboxy group-containing polymer preferably contains a carboxy group-containing recurring unit. Preferably, the carboxy group-containing recurring unit has the formula (2).

##STR00020##

[0035] In the formula (2), R.sup.A is a hydrogen atom, fluorine atom, methyl group, or trifluoromethyl group. X.sup.A is a single bond, phenylene group, naphthylene group, or *C(?O)OX.sup.A1. X.sup.A1 is a C.sub.1-C.sub.10 saturated hydrocarbylene group, phenylene group, or naphthylene group, and the saturated hydrocarbylene group may contain a hydroxy group, ether bond, ester bond, or lactone ring. * designates a valence bond to a carbon atom in a main chain.

[0036] Examples of the carboxy group-containing recurring unit are shown below, but not limited thereto. Herein R.sup.A is as defined above.

##STR00021## ##STR00022## ##STR00023##

[0037] The carboxy group-containing polymer may further contain a recurring unit other than the carboxy group-containing recurring unit (hereinafter, also referred to as another recurring unit). Another recurring unit is not particularly limited, and a recurring unit is preferable that is capable of improving the solubility, in a solvent, of an insoluble polymer containing only a recurring unit having a carboxy group. Another recurring unit preferably has a C.sub.1-C.sub.20 hydrocarbyl group which may contain at least one selected from a fluorine atom, a hydroxy group other than a phenolic hydroxy group, a cyano group, a carbonyl group, an ester bond, an ether bond, a sulfide bond, a carbonate bond, a lactone ring, and a sultone ring.

[0038] Examples of another recurring unit are shown below, but not limited thereto. Herein R.sup.A is as defined above.

##STR00024## ##STR00025## ##STR00026## ##STR00027## ##STR00028## ##STR00029## ##STR00030## ##STR00031## ##STR00032## ##STR00033## ##STR00034## ##STR00035## ##STR00036## ##STR00037## ##STR00038## ##STR00039##

##STR00040## ##STR00041## ##STR00042## ##STR00043## ##STR00044## ##STR00045## ##STR00046## ##STR00047## ##STR00048## ##STR00049## ##STR00050##

[0039] In the carboxy group-containing polymer, the carboxy group-containing recurring unit and another recurring unit are preferably present in a content ratio (molar ratio) of carboxy group-containing recurring unit: another recurring unit=10:90 to 90:10, more preferably 15:85 to 85:15, and still more preferably 20:80 to 80:20.

[0040] The carboxy group-containing polymer preferably has a weight average molecular weight (Mw) of 1000 to 500000, and more preferably 3000 to 100000. In the invention, Mw represents a value measured by gel permeation chromatography (GPC) versus polystyrene standards using tetrahydrofuran (THF) as a solvent.

[0041] If the carboxy group-containing 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 after exposure. The influences of Mw and Mw/Mn become stronger as the pattern rule becomes finer. Therefore, the carboxy group-containing polymer should preferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0 in order to provide a resist composition suitable for micropatterning to a small feature size.

[0042] Examples of the method of synthesizing the carboxy group-containing polymer include a method in which monomers corresponding to the foregoing recurring units are dissolved in an organic solvent, a radical polymerization initiator is added thereto, and the resulting mixture is heated for polymerization.

[0043] Examples of the organic solvent used in the polymerization reaction include toluene, benzene, THF, diethyl ether, dioxane, cyclohexane, cyclopentane, methyl ethyl ketone (MEK), propylene glycol monomethyl ether acetate (PGMEA), and ?-butyrolactone (GBL). Examples of the polymerization initiator include 2,2-azobisisobutyronitrile (AIBN), 2,2-azobis(2,4-dimethylvaleronitrile), dimethyl-2,2-azobis(2-methylpropionate), 1,1-azobis(1-acetoxy-1-phenylethane), benzoyl peroxide, and lauroyl peroxide. The amount of such an initiator added is preferably 0.01 to 25 mol % per total amount of monomers to be polymerized. The reaction temperature is preferably 50 to 150? C., and more preferably 60 to 100? C. The reaction time is preferably 2 to 24 hours, and more preferably 2 to 12 hours from the viewpoint of production efficiency.

[0044] The polymerization initiator may be added to the monomer solution before supply to a reaction vessel, or an initiator solution may be prepared separately from the monomer solution and each solution may be supplied to a reaction vessel independently. Radicals generated from the initiator during waiting time may promote a polymerization reaction to generate an ultrahigh polymer. Therefore, from the viewpoint of quality control, each of the monomer solution and the initiator solution is preferably prepared and added dropwise independently. The acid labile group introduced into the monomer may be used as it is, or may be protected or partially protected after polymerization. Further, a known chain transfer agent such as dodecyl mercaptan or 2-mercaptoethanol may be used in combination for adjusting the molecular weight. In this case, the amount of such a chain transfer agent added is preferably 0.01 to 20 mol % per total amount of monomers to be polymerized.

[0045] The amount of each monomer in the monomer solution is to be appropriately set, for example, so as to achieve the foregoing preferred content ratio of the recurring unit.

[0046] In the resist composition, the hypervalent iodine compound and the carboxy group-containing polymer are preferably present in a content ratio such that the molar ratio of the hypervalent iodine compound to the carboxylic acid-containing recurring unit in the polymer is 10:90 to 90:10, more preferably 20:80 to 80:20, and still more preferably 30:70 to 70:30. The hypervalent iodine compound may be used alone or in admixture of two or more having different composition ratios and different values of Mw and/or Mw/Mn. The carboxy group-containing polymer may be used alone or in admixture of two or more having different composition ratios and different values of Mw and/or Mw/Mn.

Solvent

[0047] The resist composition contains a solvent. The solvent is not particularly limited as long as the hypervalent iodine compound, the carboxy group-containing polymer, and other components described below are dissolvable therein and a film can be formed from the resulting solution. The solvent is preferably an organic solvent, and examples of the organic solvent include ketones such as cyclohexanone, methyl-2-n-pentyl ketone, and methyl isoamyl ketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, diacetone alcohol, 4-methyl-2-pentanol, and methyl 2-hydroxyisobutyrate; 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, 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; carboxylic acids such as formic acid, acetic acid, and propionic acid, lactones such as ?-butyrolactone, and mixtures thereof.

[0048] In the resist composition, the solvent is preferably present in such amounts that the resist composition may have a solids concentration of 0.1 to 20% by weight, more preferably 0.1 to 15% by weight, even more preferably 0.1 to 10% by weight. As used herein, the term solids is a general term for all components in the resist composition excluding the solvent.

Other Components

[0049] The resist composition may further contain a surfactant. The surfactant is preferably a fluorine-based and/or silicon-based surfactant. Exemplary surfactants are described, for example, in US 2008/0248425, paragraph [0276]. Also useful are surfactants other than the fluorine-based and/or silicon-based surfactants, as described, for example, in US 2008/0248425, paragraph [0280].

[0050] When used, the surfactant is preferably present in an amount of 0.0001 to 2% by weight based on the overall solids. The surfactant may be used alone or in admixture.

[0051] The resist composition may further contain a radical scavenger. When added, the radical scavenger is effective for controlling photo-reaction and adjusting sensitivity during photolithography.

[0052] Suitable radical scavengers include hindered phenols, quinones, hindered amines, and thiol compounds. Exemplary hindered phenols include dibutylhydroxytoluene (BHT) and 2,2-methylenebis(4-methyl-6-tert-butylphenol). Exemplary quinones include 4-methoxyphenol (or methoquinone) and hydroquinone. Exemplary hindered amines include 2,2,6,6-tetramethylpyperidine and 2,2,6,6-tetramethylpyperidine-N-oxy radical. Exemplary thiol compounds include dodecanethiol and hexadecanethiol.

[0053] When used, the radical scavenger is preferably present in an amount of 0.01 to 10% by weight based on the overall solids. The radical scavenger may be used alone or in admixture.

[0054] As described above, the resist composition contains the hypervalent iodine compound and the carboxy group-containing polymer as main components, but not a polymer containing an acid labile group and a photoacid generator as used in conventional chemically amplified resist compositions. Nevertheless, this resist composition works such that the region thereof exposed to EB or EUV turns soluble in the developer to form a positive tone pattern. Although its mechanism is not well understood, the following mechanism is presumed.

[0055] The hypervalent iodine compound is a three-coordinate compound having bonded thereto an aryl group and two carboxylate ligands as represented by the formula (1). When such a three-coordinate iodine compound is mixed with a carboxylic acid, replacement of carboxylate ligands takes place as equilibration reaction. If the original carboxylate ligands are removed by any suitable means, a hypervalent iodine compound having new ligands is created. For example, if iodobenzene diacetate which is relatively readily available as the hypervalent iodine compound is mixed with a carboxylic acid having a high molecular weight, and the resulting low-boiling acetic acid is removed, then ligand exchange is completed. Here, when the carboxylic acid is a polymer, the polymers are crosslinked by the hypervalent iodine compound to form a high molecular weight hypervalent iodine compound.

[0056] The polymers crosslinked by the hypervalent iodine compound are generated during film formation. This is because even if synthesized in advance, such crosslinked polymers are insoluble in most organic solvents, so that it is impossible to prepare their solution. This is presumed to be because the hypervalent iodine compound, which is originally low in solvent solubility due to the large polarization, further deteriorates in solubility by using a carboxylic acid-containing polymer that is a high molecular weight compound as a ligand. Therefore, it is desirable that the original low-molecular-weight carboxylic acid is removed during film formation and a subsequent bake step to complete a ligand exchange reaction and form a resist film in the step.

[0057] The resist film obtained from the inventive resist composition contains polymers crosslinked by the hypervalent iodine compound that are generated during film formation, and thus has extremely low organic solvent solubility. However, the iodine compound is decomposed with light to form a monovalent iodine compound, and at the same time, the crosslinking between the polymers is released to reduce the molecular weight. It is presumed that as a result, the exposed region becomes soluble in a developer which is an organic solvent and functions in positive tone.

[0058] From the foregoing presumption, the inventive resist composition is a non-chemically amplified resist composition, and does not need a polymer containing an acid labile group and a photoacid generator as used in conventional chemically amplified resist compositions. Therefore, a small size pattern can be resolved without an adverse effect (for example, image blur) due to acid diffusion.

[0059] The inventive resist composition is quite effective in the EUV lithography. This is because an iodine atom having a high absorptivity to EUV radiation is included. That is, shot noise is reduced, and higher resolution and lower LWR are achievable.

[0060] As the EUV lithography resist composition capable of forming a small size pattern, a metal resist composition based on a metal (specifically tin) compound having a high absorptivity to EUV radiation like iodine atom is known, for example, from Patent Document 2. However, the metal resist composition suffers from many problems including a lack of solvent solubility, poor shelf stability, and defects in the form of post-etching residues due to the containment of metal elements, as discussed previously. In contrast, since the inventive resist composition does not use metal elements, it is advantageous in defectiveness over the metal resist and eliminates the problem of solvent solubility. Using the inventive resist composition, a positive tone pattern is formed without development or through organic solvent development. In the step of forming contact holes, for example, the reversal processing step as conducted in negative tone development is unnecessary. From these aspects, the inventive resist composition is regarded more useful than the metal resist composition.

[0061] JP-A 2015-180928 and JP-A 2018-95853 describe a resist composition comprising a hypervalent iodine compound as an additive and a resist composition comprising a base polymer having a hypervalent iodine compound incorporated in its framework. It is described in these patent documents that these resist compositions are successful only in improving line edge roughness. They refer nowhere to a possibility of photo-decomposition of the hypervalent iodine compound and an ability to function as a non-chemically amplified resist material. Further, according to the description regarding the compounding amount and specific examples, the hypervalent iodine compound is not a main component in these resist compositions. It is then believed that a material capable of reducing shot noise during the EUV lithography and forming a small size pattern as the non-chemically amplified material is not conceivable from these patent documents. That is, the present invention provides a definitely novel resist composition and pattern forming process.

Pattern Forming Process

[0062] When the resist composition is used in the fabrication of various integrated circuits, any well-known lithography techniques are applicable. For example, the invention provides a pattern forming process comprising the steps of applying the resist composition onto a substrate to form a resist film thereon, exposing the resist film to high-energy radiation, and optionally developing the exposed resist film in a developer.

[0063] First, the resist composition is applied onto a substrate for integrated circuit fabrication (e.g., Si, SiO.sub.2, SiN, SiON, TiN, WSi, BPSG, SOG, or organic antireflective coating) or a substrate for mask circuit fabrication (e.g., Cr, CrO, CrON, MoSi.sub.2, or SiO.sub.2) by any suitable technique such as spin coating, roll coating, flow coating, dip coating, spray coating, or doctor coating. The coating is prebaked on a hot plate at a temperature of preferably 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 having a thickness of 0.01 to 2 ?m.

[0064] Next the resist film is exposed to high-energy radiation. The radiation is selected from among UV, deep UV, EB, EUV, X-ray, soft X-ray, excimer laser radiation, ?-ray, and synchrotron radiation. On use of UV, deep UV, EUV, X-ray, soft X-ray, excimer laser radiation, T-ray, and synchrotron radiation as the high-energy radiation, the resist film is exposed thereto directly or through a mask having the desired pattern so as to reach a dose of preferably about 1 to 300 mJ/cm.sup.2, more preferably about 10 to 200 mJ/cm.sup.2. On use of EB as the high-energy radiation, imagewise writing is performed directly or through a mask having the desired pattern so as to reach a dose of preferably about 0.1 to 2,000 ?C/cm.sup.2, more preferably about 0.5 to 1,500 ?C/cm.sup.2. The resist composition is best suited in micropatterning using EB or EUV as the high-energy radiation.

[0065] If necessary, the resist film is post-exposure baked (PEB). Preferably PEB is performed on a hot plate or in an oven at 30 to 150? C. for 10 seconds to 30 minutes, more preferably at 60 to 120? C. for 30 seconds to 20 minutes.

[0066] After the exposure or PEB, the resist film is developed in a developer to form a pattern, if necessary. In the practice of the invention, the exposed region of the resist film is solubilized through organic solvent development to form a positive tone pattern. The organic solvent used as the developer is preferably selected from 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone, methylcyclohexanone, acetophenone, methylacetophenone, isopropyl alcohol, n-butanol, n-pentanol, propyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, butenyl acetate, isopentyl acetate, propyl formate, butyl formate, isobutyl formate, pentyl formate, isopentyl formate, methyl valerate, methyl pentenoate, methyl crotonate, ethyl crotonate, 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, 2-phenylethyl acetate, 2-propanol, 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, diacetone alcohol, and 4-methyl-2-pentanol. These organic solvents may be used alone or in admixture of two or more.

[0067] At the end of development, the resist film is rinsed if necessary. 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.

[0068] Rinsing is effective for preventing the resist pattern from collapse or reducing defect formation. Rinsing is not essential. By omitting rinsing, the amount of the solvent used is saved.

EXAMPLES

[0069] Synthesis Examples, Examples, and Comparative Examples of the invention are given below by way of illustration and not by way of limitation.

[1] Synthesis of Polymer

[0070] The following monomers were used for synthesis of polymers.

##STR00051## ##STR00052##

Synthesis Example 1 Synthesis of Polymer P-1

[0071] In a nitrogen atmosphere, a monomer a-1 (56 g), a monomer b-1 (105 g), V-601 (manufactured by FUJIFILM Wako Pure Chemical Corporation) (5.4 g), and MEK (180 g) were put into a flask to prepare a monomer-polymerization initiator solution. In another flask under a nitrogen atmosphere, 55 g of MEK was put and heated to 80? C. while stirred, and then the monomer-polymerization initiator solution was added dropwise over 4 hours. After completion of the dropwise addition, stir of the polymerization liquid was continued for 2 hours while the liquid temperature was maintained at 80? C., and then the polymerization liquid was cooled to room temperature. The obtained polymerization liquid was added dropwise to 4000 g of vigorously stirred hexane, and the precipitated polymer was separated by filtration. The obtained polymer was washed twice with hexane (1200 g), and then vacuum-dried at 50? C. for 20 hours to obtain a polymer P-1 in the form of a white powder (yield: 155 g, yield rate: 96%). The polymer P-1 had a value of Mw of 7700, and a value of Mw/Mn of 1.82. The value of Mw was measured by GPC versus polystyrene standards using THF as a solvent.

##STR00053##

Synthesis Examples 2 to 12 Synthesis of Polymer P-2 to P-12

[0072] Polymers shown in Table 1 was synthesized in the same manner as in Synthesis Example 1 except that the kind and the compounding ratio of each monomer were changed.

TABLE-US-00001 TABLE 1 Introduction Introduction Unit ratio Unit ratio Polymer 1 (mol %) 2 (mol %) Mw Mw/Mn P-1 a-1 65 b-1 35 7,700 1.82 P-2 a-1 50 b-2 50 8,400 1.84 P-3 a-1 60 b-3 40 8,100 1.79 P-4 a-2 65 b-1 35 7,900 1.79 P-5 a-2 50 b-2 50 8,300 1.83 P-6 a-2 60 b-3 40 8,200 1.82 P-7 a-3 65 b-1 35 8,000 1.80 P-8 a-3 50 b-2 50 8,600 1.84 P-9 a-3 60 b-3 40 7,900 1.81 P-10 c-1 60 c-2 40 9,800 1.82 P-11 a-1 70 b-1 30 8,000 1.84 P-12 a-1 80 b-1 20 7,900 1.82

[2] Preparation of Resist Composition

Examples 1-1 to 1-15 and Comparative Examples 1-1 to 1-2

[0073] Resist compositions (R-01 to R-15) were prepared by dissolving a hypervalent iodine compound and a polymer in a solvent containing 0.01% by weight of a surfactant (PF-636, manufactured by OMNOVA Solutions Inc.) in accordance with the recipe shown in Table 2, and filtering the solution through a Teflon (registered trademark) filter having a pore size of 0.2 ?m. Separately, comparative resist compositions (CR-01 to CR-02) were prepared by dissolving a polymer, a photoacid generator, and a sensitivity modifier in a solvent containing 0.01% by weight of a surfactant (PF-636, manufactured by OMNOVA Solutions Inc.) in accordance with the recipe shown in Table 3, and filtering the solution through a Teflon (registered trademark) filter having a pore size of 0.2 ?m.

TABLE-US-00002 TABLE 2 Hypervalent iodine Resist compound Polymer Solvent 1 Solvent 2 composition (pbw) (pbw) (pbw) (pbw) Example 1-1 R-01 I-1 (10) P-1 (15) PGMEA (800) AcOH (200) 1-2 R-02 I-2 (13) P-1 (15) PGMEA (800) AcOH (200) 1-3 R-03 I-3 (11) P-1 (15) PGMEA (800) AcOH (200) 1-4 R-04 I-1 (10) P-2 (18) PGMEA (800) AcOH (200) 1-5 R-05 I-1 (10) P-3 (17) PGMEA (800) AcOH (200) 1-6 R-06 I-1 (10) P-4 (26) PGMEA (800) AcOH (200) 1-7 R-07 I-1 (10) P-5 (29) PGMEA (800) AcOH (200) 1-8 R-08 I-1 (10) P-6 (28) PGMEA (800) AcOH (200) 1-9 R-09 I-1 (10) P-7 (19) PGMEA (800) AcOH (200) 1-10 R-10 I-1 (10) P-8 (22) PGMEA (800) AcOH (200) 1-11 R-11 I-1 (10) P-9 (21) PGMEA (800) AcOH (200) 1-12 R-12 I-1 (9) P-11 (15) HBM (800) AcOH (200) 1-13 R-13 I-1 (8) P-12 (15) HBM (800) PA (200) 1-14 R-14 I-1 (10) P-1 (15) HBM (800) PA (200) 1-15 R-15 I-1 (10) P-1 (15) HBM (1000)

TABLE-US-00003 TABLE 3 Photoacid Sensitivity Resist Polymer generator modifier Solvent 1 Solvent 2 composition (pbw) (pbw) (pbw) (pbw) (pbw) Comparative 1-1 CR-01 P-1 PAG-1 Q-1 PGMEA GBL Example (80) (19) (6) (1890) (210) 1-2 CR-02 P-1 PAG-1 I-1 PGMEA GBL (80) (19) (5) (1890) (210)

[0074] In Tables 2 and 3, the hypervalent iodine compound (I-1 to I-3), the photoacid generator PAG-1, the sensitivity modifier Q-1, and the solvent are identified below.

##STR00054##

Solvent:

[0075] PGMEA (propylene glycol monomethyl ether acetate) [0076] AcOH (acetic acid) [0077] GBL (?-butyrolactone) [0078] HBM (methyl 2-hydroxyisobutyrate) [0079] PA (propionic acid)

[3] EUV Lithography Test (Line-and-Space)

Examples 2-1 to 2-15 and Comparative Examples 2-1 to 2-2

[0080] Each of the resist compositions (R-01 to R-15, CR-01 to CR-02) was spin coated on a silicon substrate having a 20-nm coating of silicon-containing spin-on hard mask SHB-A940 (Shin-Etsu Chemical Co., Ltd., silicon content 43 wt %) and prebaked (PAB) on a hotplate at the temperature shown in Table 4 for 60 seconds to form a resist film of 40 nm thick. Using an EUV scanner NXE3400 (ASML, NA 0.33, a 0.9, 900 dipole illumination), the resist film was exposed to EUV through a mask bearing a 36-nm 1:1 line-and-space (LS) pattern. The resist film was baked (PEB) on a hotplate at the temperature shown in Table 4 for 60 seconds and developed in the developer shown in Table 4 for 30 seconds to form a LS pattern having a space width of 18 nm and a pitch of 36 nm.

[0081] The obtained resist pattern was evaluated as follows. Table 4 shows the results.

Evaluation of Sensitivity

[0082] The LS pattern was observed under CD-SEM (CG-6300, Hitachi High-Tech Corporation), and the optimum dose (Eop, mJ/cm.sup.2) which provided an LS pattern with a space width of 18 nm and a pitch of 36 nm was determined and reported as sensitivity.

Evaluation of LWR

[0083] An LS pattern was formed by exposure in the optimum dose (Eop). The space width was measured under CD-SEM (CG-6300, Hitachi High-Tech Corporation) at longitudinally spaced apart 10 points, from which a 3-fold value (3a) of the standard deviation (?) was determined and reported as LWR. A smaller value indicates a pattern having a lower roughness and more uniform space width.

Evaluation of Maximum Resolution

[0084] An LS pattern was formed while increasing the exposure dose little by little from the optimum dose (Eop). The line width (nm) which could be resolved was determined under CD-SEM (CG-6300, Hitachi High-Tech Corporation) and reported as maximum resolution (nm). A smaller value indicates a pattern having a better maximum resolution and smaller feature size.

TABLE-US-00004 TABLE 4 Maximum Resist PAB/PEB Eop LWR resolution composition (? C.) Developer (mJ/cm.sup.2) (nm) (nm) Example 2-1 R-01 130/90 nBA 39 3.6 14 2-2 R-02 130/90 nBA 39 3.6 14 2-3 R-03 130/90 nBA 36 3.4 16 2-4 R-04 130/90 nBA 42 3.8 13 2-5 R-05 130/90 nBA 44 3.5 13 2-6 R-06 130/90 nBA 45 3.7 16 2-7 R-07 130/90 nBA 44 3.8 16 2-8 R-08 130/90 nBA 45 3.6 16 2-9 R-09 130/90 nBA 40 3.5 16 2-10 R-10 130/90 nBA 42 3.7 14 2-11 R-11 130/90 nBA 42 3.4 16 2-12 R-12 130/90 nBA 38 3.6 16 2-13 R-13 130/90 nBA 37 3.5 16 2-14 R-14 130/90 nBA 40 3.6 14 2-15 R-15 130/90 nBA 40 3.6 14 Comparative 2-1 RC-01 105/90 TMAH 80 4.5 18 Example 2-2 RC-02 105/90 TMAH 85 4.8 18

Developer:

[0085] nBA (butyl acetate) [0086] TMAH (2.38 wt % aqueous tetramethylammonium hydroxide solution)

[0087] It is evident from Table 4 that the resist compositions within the scope of the invention form LS patterns having satisfactory sensitivity, LWR, and resolution when processed by the EUV lithography.

[4] EUV Lithography Test (Contact Hole Pattern)

Examples 3-1 to 3-15 and Comparative Examples 3-1 to 3-2

[0088] Each of the resist compositions (R-01 to R-15, CR-01 to CR-02) was spin coated on a silicon substrate having a 20-nm coating of silicon-containing spin-on hard mask SHB-A940 (Shin-Etsu Chemical Co., Ltd., silicon content 43 wt %) and baked (PAB) on a hotplate at the temperature shown in Table 5 for 60 seconds to form a resist film of 50 nm thick. Using an EUV scanner NXE3400 (ASML, NA 0.33, a 0.9/0.6, quadrupole illumination), the resist film was exposed to EUV through a mask bearing a hole pattern with a pitch of 64 nm+20% bias (on-wafer size). After exposure, the resist film was baked (PEB) on a hotplate at the temperature shown in Table 5 for 60 seconds and developed in the developer shown in Table 5 for 30 seconds to form a hole pattern having a size of 32 nm.

[0089] The obtained resist pattern was evaluated as follows. Table 5 shows the results.

Evaluation of Sensitivity

[0090] The contact hole pattern was observed under CD-SEM (CG-6300, Hitachi High-Tech Corporation), and the optimum dose (Eop, mJ/cm.sup.2) which provided a hole pattern with a size of 22 nm was determined and reported as sensitivity.

Evaluation of CDU

[0091] The size of 50 holes which were printed at Eop was measured, from which a 3-fold value (3?) of the standard deviation (?) was computed and reported as CDU. A smaller value of CDU indicates a hole pattern with more uniform hole diameter.

Evaluation of Maximum Resolution

[0092] A hole pattern was formed while reducing the exposure dose little by little from the optimum dose (Eop). The hole diameter (nm) which could be resolved was determined under CD-SEM (CG-6300, Hitachi High-Tech Corporation) and reported as maximum resolution. A smaller value indicates a pattern having a better maximum resolution and smaller hole diameter.

TABLE-US-00005 TABLE 5 Maximum Resist PAB/PEB Eop LWR resolution composition (? C.) Developer (mJ/cm.sup.2) (nm) (nm) Example 3-1 R-01 130/90 nBA 24 2.7 26 3-2 R-02 130/90 nBA 26 2.7 26 3-3 R-03 130/90 nBA 26 2.8 28 3-4 R-04 130/90 nBA 28 2.8 24 3-5 R-05 130/90 nBA 28 2.7 26 3-6 R-06 130/90 nBA 26 2.9 28 3-7 R-07 130/90 nBA 25 2.9 26 3-8 R-08 130/90 nBA 27 2.7 26 3-9 R-09 130/90 nBA 28 2.6 28 3-10 R-10 130/90 nBA 29 2.8 28 3-11 R-11 130/90 nBA 28 2.6 26 3-12 R-12 130/90 nBA 23 2.7 28 3-13 R-13 130/90 nBA 23 2.6 28 3-14 R-14 130/90 nBA 25 2.8 26 3-15 R-15 130/90 nBA 25 2.6 25 Comparative 3-1 RC-01 105/90 TMAH 42 3.8 32 Example 3-2 RC-02 105/90 TMAH 40 4.0 32

[0093] It is evident from Table 5 that the resist compositions within the scope of the invention form contact hole patterns having satisfactory sensitivity, CDU, and resolution when processed by the EUV lithography.

[0094] Japanese Patent Application No. 2022-208497 is incorporated herein by reference. Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.