US 20140080064A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2014/0080064 A1 Hatakeyama (43) Pub. Date: Mar. 20, 2014
(54) RESIST PROTECTIVE FILM-FORMING Publication Classi?cation COMPOSITION AND PATTERNING PROCESS (51) Int. Cl. (71) Applicant: SHIN-ETSU CHEMICAL CO., LTD., G03F 7/11 (2006-01) Tokyo (JP) G03F 7/20 (2006.01) G03F 7/30 (2006.01) (72) Inventor: Jun Hatakeyama, Joetsu-shi (JP) (52) US‘ Cl‘ CPC .. G03F 7/11 (2013.01); G03F 7/30 (2013.01); G03F 7/20 (2013.01) (73) Assigneez SHIN_ETSU CHEMICAL CO” LTD” USPC ...... 430/296; 526/242; 526/243; 524/378; Tokyo (JP) 430/325; 430/322 (57) ABSTRACT A pattern is printed by forming a photoresist layer on a Wafer, (21) APP1~ NOJ 14/022-1445 forming a protective ?lm thereon, exposure, and develop ment. The protective ?lm is formed from a composition com prising a copolymer comprising recurring units derived from (22) Filed: Sep. 10, 2013 a styrene, indene, benZofuran or benZothiophene monomer having 1,1,1,3,3,3-hexa?uoro-2-propanol, and recurring (30) Foreign Application Priority Data units derived from a styrene, vinylnaphthalene, indene, ben Zofuran, benZothiophene, stilbene, styrylnaphthalene or Sep. 14, 2012 (JP) ...... 2012-202464 dinaphthylethylene monomer and an ether solvent. US 2014/0080064 A1 Mar. 20, 2014
RESIST PROTECTIVE FILM-FORMING pointed out that the sensitivity of resist material can be COMPOSITION AND PATTERNING PROCESS increased at the sacri?ce of resolution and edge roughness (LER, LWR). CROSS-REFERENCE TO RELATED [0008] EUV resist materials are susceptible to environmen APPLICATION tal impacts because of their high sensitivity. In general, an amine quencher is added to chemically ampli?ed resist mate [0001] This non-provisional application claims priority rials for rendering the resist materials unsusceptible to con under 35 U.S.C. §ll9(a) on Patent Application No. 2012 tamination With airborne amine. The amount of amine 202464 ?led in Japan on Sep. 14, 2012, the entire contents of quencher added to the EUV resist materials is only a fraction Which are hereby incorporated by reference. as compared With the ArF and other lithography resist mate rials. As a result, the EUV resist materials tend to take a T-top TECHNICAL FIELD pro?le under the in?uence of amine from the resist surface. [0002] This invention relates to a composition for forming [0009] For shutting off environmental impacts, it is effec a resist protective ?lm for use in the micropatterning step in tive to form a protective ?lm on top of the resist ?lm. Appli the fabrication of semiconductor devices, and a pattern form cation of a protective ?lm Was effective for the chemically ing process using the same. ampli?ed resist materials of the early stage based on a t-BOC protected polyhydroxystyrene and free of an amine quencher, BACKGROUND OF THE INVENTION used in the KrF excimer laser lithography. Also at the initial stage of the ArF immersion lithography, a protective ?lm Was [0003] In the drive for higher integration and operating applied to prevent the acid generator from leaching out in speeds in LSI devices, the pattern rule is made drastically Water and thus inhibit the pro?le from becoming T-topped. ?ner. The rapid advance toWard ?ner pattern rules is grounded Patent Document 1 discloses a protective ?lm material based on the development of a projection lens With an increased NA, on a homopolymer of styrene having l,l,l,3,3,3-hexa?uoro a resist material With improved performance, and a light 2-propanol or a copolymer thereof With methacrylate. source With a shorter Wavelength. [0010] With respect to the EUV lithography, it Was also [0004] Resist materials adapted for KrF excimer laser (248 proposed to form a protective ?lm on top of the resist ?lm (see nm) started use on the 0.3 pm process and entered the mass Patent Documents 2 to 4 and Non-Patent Document 1). The production phase on the 0.13 pm rule. A Wavelength change protective ?lm thus formed is effective for improving envi over from KrF to shorter Wavelength ArF excimer laser (193 ronmental resistance and reducing the outgassing from the nm) is expected to enable miniaturization of the design rule to resist ?lm. beloW 0.13 pm. Since commonly used novolak resins and [0011] EUV laser sources of the discharge-produced polyvinylphenol resins have very strong absorption in prox plasma (DPP) or laser-produced plasma (LPP) method emit imity to 193 nm, they cannot be used as the base resin for not only light of Wavelength 13.5 nm available for pattern resists. To ensure transparency and dry etching resistance, formation, but also broad light (though Weak) of Wavelength acrylic resins and alicyclic (typically cycloole?n) resins are 140 to 300 nm, knoWn as out-of-band (OOB) light. The broad investigated, leading to mass-scale production of devices by light has a loW intensity, but a Wide span of Wavelength and is the ArF lithography. not negligible as energy quantity. The EUV microstepper is [0005] For the next 45-nm node devices Which required an loaded With a Zr ?lter for cutting off OOB light, but the advancement to reduce the Wavelength of exposure light, the quantity of light is reduced thereby. The EUV scanner may F2 lithography of 157 nm Wavelength became a candidate. not be loaded With the ?lter because a reduction of light HoWever, for the reasons that the projection lens uses a large quantity is not permissible for the goal of enhancing the amount of expensive CaF2 single crystal, the scanner thus throughput. becomes expensive, hard pellicles are introduced due to the [0012] There is a need for a resist material Which is sensi extremely loW durability of soft pellicles, the optical system tive to EUV, but not to OOB light. For such resist materials, must be accordingly altered, and the etch resistance of resist the cation structure of sulfonium salt PAG is important. Patent is loW; the F2 lithography Was postponed and instead, the Document 5 (JP-A 2011-138107, paragraph early introduction of ArF immersion lithography Was advo [0013] describes a polymer-bound acid generator having cated. This enables mass-scale production of 45-nm node a high sensitivity to EUV light, but a loW sensitivity to devices. For the mass-scale production of 32-nm node OOB light. Non-Patent Document 1 describes the supe devices, the double patterning process utiliZing sideWall riority of a protective ?lm Which is formed on top of the spacer technology is used although the process suffers from resist layer for cutting off OOB light. complexity and length. [0014] As the resist protective ?lm, a number of materials [0006] For the fabrication of 32-nm node and subsequent have been proposed in the ArF immersion lithography appli devices, the EUV lithography using an exposure Wavelength cation. Among others, Patent Document 6 discloses a protec of 13.5 nm Which is shorter than the conventional lasers by tive ?lm material comprising recurring units of hexa?uoro one order of magnitude and thus featuring improved resolu alcohol-containing styrene although it is considered tion is expected rather than the double patterning process With practically unacceptable because of very high absorption at noticeable costs. Efforts are focused on the EUV lithography. Wavelength 193 nm. [0007] In the EUV lithography, a loW laser poWer and light [0015] In connection With a protective ?lm for use in the attenuation by re?ecting mirror lead to a reduced quantity of immersion lithography, it is pointed out in Patent Document 7 light. Then light With a loW intensity reaches the Wafer sur that the solvent for the coating of a protective ?lm dissolves face. It is urgently demanded to develop a high-sensitivity the resist ?lm surface to invite interrnixing betWeen the pro resist material in order to gain a throughput despite a loW light tective ?lm and the resist ?lm, resulting in a thickness loss of quantity. HoWever, a trade-off relationship of sensitivity is the resist pattern after development. The ?lm thickness loss US 2014/0080064 A1 Mar. 20, 2014
becomes outstanding particularly When alcohol solvents are ?uorine atoms possesses strong absorption. Nevertheless, the used. Ether solvents are effective for preventing a ?lm thick hexa?uoroalcohol-containing polymers are advantageous in ness loss. Polymers that are dissolvable in ether solvents that they are soluble in ether solvents that cause little or no include polymers containing hexa?uoroalcohol (HFA) as damages to the resist ?lm. described in Patent Document 5. However, since ?uorine [0028] It is reported that polyhydroxystyrene-based resist atoms have strong absorption to EUV light, a resist ?lm on materials have a high acid generation e?iciency upon EUV Which a protective ?lm is formed using a HFA-containing exposure. The EUV exposure brings about energy transfer polymer undesirably exhibits a loW sensitivity on patterning. from phenol group to the acid generator to exert a sensitiZing effect, leading to enhanced sensitivity. Therefore, polyhy CITATION LIST droxystyrene-based resist materials are investigated for the [0016] Patent Document 1: JP-A 2006-053300 purpose of enhancing the sensitivity of resist ?lm. [0017] Patent Document 2: JP-A 2006-058739 (WO [0029] JP 4425776 proposes a resist material based on a 20061 12306) polymer having an acid generator (PAG) bound to its back [0018] Patent Document 3: JP 4716047 bone. On use of a sulfonium or iodonium salt acid generator [0019] Patent Document 4: JP-A 2008-065304 Whose sulfonic acid is bound to the backbone, the distance of [0020] Patent Document 5: JP-A 2011-138107 acid diffusion is shortened, thereby minimiZing image blur [0021] Patent Document 6: JP-A 2005-352384 (US due to acid diffusion. This is advantageous in forming ?ne 7316886) siZe patterns. One shortcoming of the resist ?lm having PAG [0022] Patent Document 7: JP 4771083 (US 20070122741) bound thereto is a loW sensitivity. The sensitivity may be [0023] Non-Patent Document 1: Proc. SPIE Vol. 7969, enhanced by copolymeriZing hydroxystyrene having a phe p796916-1 (2011) nol group or the like. HoWever, copolymeriZation of a mono mer having a phenol group capable of enhancing an alkaline SUMMARY OF INVENTION dissolution rate is not desirable because a thickness loss of the resist pattern can occur. There is a need for a resist protective [0024] An object of the invention is to provide a resist ?lm-forming composition Which alloWs the resist ?lm to protective ?lm-forming composition Which is effective for exhibit a high sensitivity and minimiZes the thickness loss of mitigating the environmental impact on a resist ?lm, cutting the resist pattern as developed. off OOB light, reducing a ?lm thickness loss of the resist pattern, avoiding bridges betWeen pattern features, alloWing [0030] In one aspect, the invention provides a resist protec the resist ?lm to exhibit a high sensitivity, and suppressing tive ?lm-forming composition Which is used in a lithography outgassing from the resist ?lm. Another object is to provide a pattern forming process comprising the steps of forming a pattern forming process using the same. photoresist layer on a Wafer, forming a protective ?lm [0025] The inventors have found that a protective ?lm thereon, exposure, and development. The resist protective formed on a resist ?lm as de?ned beloW is effective for ?lm-forming composition comprises a copolymer compris mitigating the environmental impact on the resist ?lm, ing recurring units (p) derived from at least one monomer absorbing OOB light, reducing a ?lm thickness loss of the selected from the group consisting of a styrene, indene, ben resist pattern, and avoiding bridges betWeen pattern features. Zofuran and benZothiophene having 1,1,1,3,3,3-hexa?uoro The protective ?lm is made soluble in alkaline developer so 2-propanol, and recurring units (ql ), (q2), (q3) or (q4) derived that it can be stripped off at the same time as development of from at least one monomer selected from the group consisting the resist ?lm. Thus the process is simple as compared With of a styrene, vinylnaphthalene, indene, benZofuran, ben the protective ?lm of solvent stripping type, and the concomi Zothiophene, stilbene, styrylnaphthalene, and dinaphthyleth tant increase of the process cost is minimized. ylene, as represented by the general formula (1), as a base [0026] It is reported that at Wavelength 13.5 nm, hydrogen, resin. carbon, silicon and sulfur atoms have loW absorption and (1) oxygen and ?uorine atoms have high absorption. The ?uo ropolymer described in Patent Document 2 possesses notice able absorption at Wavelength 13.5 nm. If the resist protective 112 ?lm is absorptive, the sensitivity of the resist ?lm is shifted to the loWer side. In the EUV lithography With a loW laser poWer, the loW sensitivity of the resist ?lm is a problem. Then the resist protective ?lm must be highly transparent. Also since the aforementioned ?uoropolymer does not dissolve in alka line developer, a stripping cup specialiZed for the protective ?lm must be separately used prior to development. As such, the process is complicated. Since a protective ?lm Which can be stripped at the same time as development of the resist ?lm is desirable, the design of protective ?lm material needs to incorporate an alkali-soluble group into the material. The protective ?lm de?ned herein meets these requirements. [0027] Suitable alkali-soluble groups include carboxyl, phenol, sulfo, and hexa?uoroalcohol groups. From the stand point of transparency, the use of a hexa?uoroalcohol group as the alkali-soluble group in the protective ?lm is undesirable because the hexa?uoroalcohol group having as many as six US 2014/0080064 A1 Mar. 20, 2014
Herein R1 is hydrogen, hydroxyl, a straight, branched or The photoresist layer is formed from a resist composition cyclic Cl-Cl0 alkyl, alkoxy, acyloxy, cyano, nitro, amino comprising a polymer comprising recurring units (al) and/or group or halogen atom, m is l or 2; R2 and R3 each are (a2) having a carboxyl group and/or phenolic hydroxyl group hydrogen, or R2 and R3, taken together, may be methylene, Whose hydrogen is substituted by an acid labile group, as iOi or iSi to form a ring; R4 to R8 are each indepen represented by the general formula (2) and having a Weight dently hydrogen, hydroxyl, a straight, branched or cyclic average molecular Weight of 1,000 to 500,000, as a base resin. Cl-Cl0 alkyl, alkoxy, acyloxy, C2-C6 alkenyl, C6-Cl0 aryl, cyano, nitro, amino, tri?uoromethyl, ester group, or halogen atom; X1 is methylene, 40* or iSi; X2 and X3 each are (Z) phenylene or naphthylene; n is an integer of l to 5, 0.lsp
ester or ether moiety, A2 is hydrogen, CF3 or carbonyl group, Zothiophene having l,l,l,3,3,3-hexa?uoro-2-propanol for Z1 is a single bond, methylene, ethylene, phenylene, ?uori alkaline solubility. The recurring units (p) are represented by nated phenylene, 4OiRO32i, or iC(:O)iZ2iRO32, the folloWing general formula. Z2 is oxygen or NH, RO32 is a straight, branched or cyclic Cl-C6 alkylene, phenylene, ?uorinated phenylene, tri?uo romethyl-substituted phenylene or alkenylene group, Which may contain a carbonyl, ester, ether or hydroxyl moiety, M' is a non-nucleophilic counter ion, 0sbls0.5, 0sb2s0.5, 0sb3s0.5, and 0 [0041] The terms “a” and “an” herein do not denote a limi c1:3 tation of quantity, but rather denote the presence of at least one of the referenced item. “Optional” or “optionally” means C113 that the subsequently described event or circumstance may or may not occur, and that the description includes instances on C113 Where the event occurs and instances Where it does not. As used herein, the notation (CM-Cm) means a group containing c1:3 from n to m carbon atoms per group. on [0042] The abbreviations and acronyms have the folloWing meaning. C113 [0043] MW: Weight average molecular Weight [0044] Mn: number average molecular Weight 0 H [0045] MW/ Mn: molecular Weight distribution or dispersity [0046] GPC: gel permeation chromatography F3C c1:3 F 3 0 c1:3 [0047] PEB: post-exposure baking on on [0048] PAG: photoacid generator [0049] LER: line edge roughness c1:3 0 [0050] LWR: line Width roughness I H C113 Protective Film-Forming Composition C113 [0051] The resist protective ?lm-forming composition comprises as a base resin a polymer comprising recurring on units (p) derived from at least one hydrocarbon monomer on C113 on selected from among a styrene, indene, benZofuran and ben US 2014/0080064 A1 Mar. 20, 2014 -continued -continued c1:3 HO S S F3C F3C c1:3 on HO c1:3 C113 F3C c1:3 on [0053] The l,l,l,3,3,3-hexa?uoro-2-propanol (HFA) group has the drawback that the sensitivity of a resist ?lm is reduced due to the high absorption of EUV by ?uorine atoms. To mitigate the drawback, preferably recurring units having a C113 HFA group are derived from styrene or indene having little OH absorption to EUV, or copolymeriZed With a monomer having c1:3 an aromatic group containing more hydrocarbon. Suitable F3C c1:3 OH recurring units resulting from copolymeriZation of a mono mer having a hydrocarbon-rich aromatic group include recur ring units (ql) to (q4) derived from a monomer selected from c1:3 among a styrene, vinylnaphthalene, indene, benZofuran, ben HO Zothiophene, stilbene, styrylnaphthalene, and dinaphthyleth F3C ylene, as represented by the general formula (1). (1) 112 F3C c1:3 OH HO OH 3%C113 C113 C113 HO 0 31 O Herein R1, R2, R3, and m are as de?ned above. R4 to R8 are O o each independently hydrogen, hydroxyl, a straight, branched C113 or cyclic Cl-Cl0 alkyl group, alkoxy group, acyloxy group, C2-C6 alkenyl group, C6-Cl0 aryl group, cyano group, nitro group, amino group, tri?uoromethyl group, ester group (iOCORO wherein R0 is C 1 -C6 alkyl), or halogen atom. X1 is methylene, 40* or iSi. X2 and X3 each are phenylene or C113 naphthylene, n is an integer ofl to 5, 0.lsp HO C55 HO US 2014/0080064 A1 Mar. 20, 2014 contmued -cont1nued \ \ \ F F \ \ \ HO HO [0055] Examples of the monomer from Which recurring units (q2) are derived are shown below. hobohi?m US 2014/0080064 A1 Mar. 20, 2014 -continued i? (9-continued \0 (I) /O \ \ \ ? g9 O\ O\ O\ Er? H019 \E O \E i ri r? 3 | \ \ O\ § @2 6 0Y0 or? K3 \ 0T1? M9 0Y0 [0056] Examples of the monomer from Which recurring units (q3) are derived are shown below. F59Y ‘i @9601? US 2014/0080064 A1 Mar. 20, 2014 _ ?ntinued _ -continued S S S HO : g O l 5 O K 5 o HO i — TS f — s F — ‘S HO HO OH — — — OH O F O O — _ _ S F S S OH F — — — OH F O O O O — — _ S S O S F F F — — — F O o o _ _ _ \O O /o \o O O Y _ _ /o O f o O o CY — — O /( O 06$ i 3 o o O S S O o O A Y O O O _ _ _ Y0 O A [0057] Examples of the monomer from Which recurring units (q4) are derived are shown below. US 2014/0080064 A1 Mar. 20, 2014 10 3%-continued 5% 1i 0 OH 0/ o)k [0058] While the copolymer for the protective ?lm is char \ \ \ acteriZed by comprising recurring units (p) and (ql) to (q4), recurring units (r) having a carboxyl or sulfo group may be copolymeriZed therein for improving the alkaline solubility of the protective ?lm, as described in JP-A 2008-065304. [0059] Although recurring units (p) derived from at least one monomer selected from among a styrene, indene, benZo furan and benZothiophene having a l,l,l,3,3,3-hexa?uoro-2 OH /o Yo propanol group (simply, hexa?uoroalcohol group) may be 0 incorporated in a molar fraction of l (p:l ), it is preferred that the recurring units (p) be copolymeriZed With recurring units US 2014/0080064 A1 Mar. 20, 2014 (q1) to (q4) of other monomers and recurring units (r) having diethyl ether, dioxane and tetrahydrofuran. These solvents a carboxyl or sulfo group in a copolymerization ratio in the may be used alone or in admixture. A Well-knoWn molecular range: Weight modi?er such as dodecyl mercaptan may be used together. [0068] For the polymerization reaction, the reaction tem perature may vary With the type of initiator or the boiling and point of solvent. The temperature is typically 20 to 2000 C., preferably 50 to 1400 C. The reactor used herein is not par OsrsO . 6; ticularly limited. preferably [0069] From the polymer solution or dispersion thus obtained, the organic solvent or Water as the reaction medium may be removed by any Well-knoWn means, for example, by reprecipitation and ?ltration, or heat distillation in vacuum. [0070] The protective ?lm-forming composition is gener and 0srs0.5; ally formulated by dissolving the copolymer in a solvent. The solvent used herein is not particularly limited as long as it and more preferably does not dissolve the photoresist ?lm. Examples of the sol vent in Which the resist ?lm can be dissolved include ketones such as cyclohexanone and methyl-2 -n-amyl ketone, alcohols such as 3-methoxybutanol, 3-methyl-3 -methoxybutanol, and 1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethyl [0060] The polymer comprising recurring units (p) derived ene glycol monoethyl ether, propylene glycol dimethyl ether, from a monomer selected from a styrene, indene, benzofuran and diethylene glycol dimethyl ether; and esters such as pro and benzothiophene having 1,1,1,3,3,3-hexa?uoro-2-pro pylene glycol monomethyl ether acetate (PGMEA), propy panol should preferably have a Weight average molecular lene glycol monoethyl ether acetate, ethyl lactate, ethyl pyru Weight (MW) in the range of 1 ,000 to 10,000, as measured by vate, butyl acetate, methyl 3-methoxypropionate, ethyl GPC versus polystyrene standards. A polymer With a MW in 3-ethoxypropionate, tert-butyl acetate, tert-butyl propionate, excess of 10,000 may be less soluble in solvents and alkaline and propylene glycol mono-tert-butyl ether acetate. These developers. A polymer With a MW of less than 1,000 may solvents should not be used herein. alloW for intermixing With the resist ?lm, leading to a ?lm [0071] Examples of the solvent Which does not dissolve the thickness loss of the resist pattern after development. photoresist ?lm and Which can be preferably used herein [0061] The polymer for the protective ?lm is generally include ether solvents such as diisopropyl ether, diisobutyl synthesized by radical copolymerization initiated With such a ether, diisopentyl ether, di-n-pentyl ether, methyl cyclopentyl radical as 2,2'-azobisisobutyronitrile (AIBN) or ion polymer ether, methyl cyclohexyl ether, di-n-butyl ether, di-sec-butyl ization (anionic polymerization) in the presence of an alkyl ether, diisopentyl ether, di-sec-pentyl ether, di-tert-amyl lithium or similar catalyst. Such polymerization may be car ether, and di-n-hexyl ether. ried out by the standard procedure. [0072] Mixtures of the ether solvents With higher alcohols [0062] Suitable radical polymerization initiators include, of 4 or more carbon atoms are also useful. Suitable higher but are not limited to, azo compounds such as alcohols of 4 or more carbon atoms include 1-butyl alcohol, [0063] 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, 1-pen [0064] 2,2'-azobis(2,4-dimethylvaleronitrile), tanol, 2-pentanol, 3-pentanol, tert-amyl alcohol, neopentyl [0065] 2,2'-azobisisobutyronitrile (AIBN), alcohol, 2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl [0066] 2,2'-azobis(2,4,4-trimethylpentane), 3 -pentanol, cyclopentanol, 1 -hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol, 3,3-dimethyl-1-butanol, 3,3-dim peroxides such as tert-butyl peroxypivalate, lauroyl peroxide, ethyl-2-butanol, 2-ethyl-1-butanol, 2-methyl-1-pentanol, benzoyl peroxide, and tert-butyl peroxylaurate. Suitable 2-methyl-2 -pentanol, 2-methyl-3 -pentanol, 3 -methyl-1-pen Water-soluble initiators are persulfates such as potassium per tanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol, 4-methyl sulfate. Also useful are redox initiators Which are obtained by 1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol, combining a peroxide such as potassium persulfate or hydro cyclopentanol, and cyclohexanol. gen peroxide With a reducing agent such as sodium sul?te. The amount of the initiator used may vary With its type, [0073] With the higher alcohol of 4 or more carbon atoms, polymerization conditions or the like. Typically the initiator is an aromatic solvent may be blended for preventing intermix used in an amount of 0.001 to 5%, preferably 0.01 to 2% by ing With the resist ?lm. Suitable aromatic solvents include Weight based on the total Weight of monomers. toluene, xylene, mesitylene, ethylbenzene, propylbenzene, [0067] For the polymerization reaction, a solvent may be butylbenzene, tert-butylbenzene, and anisole. used. Any solvents may be used as long as they do not retard [0074] Preferably the ether solvent accounts for at least polymerization reaction. Suitable solvents include esters 50% by Weight, more preferably at least 60% by Weight based such as ethyl acetate and n-butyl acetate, ketones such as on the total Weight of the solvent mixture. acetone, methyl ethyl ketone, and methyl isobutyl ketone, [0075] The solvent (or solvent mixture) is preferably used aliphatic or aromatic hydrocarbons such as toluene, xylene in an amount of 100 to 30,000 parts, more preferably 200 to and cyclohexane, alcohols such as isopropyl alcohol and eth 20,000 parts by Weight per 100 parts by Weight of the base ylene glycol monomethyl ether, and ether solvents such as res1n. US 2014/0080064 A1 Mar. 20, 2014 [0076] An acid generator may be added to the protective group or a naphthylene group. Y2 is a single bond, an ester ?lm-forming composition. Typical of the acid generator used group or an amide group, 0sa1s0.9, 0sa2sa2s0.9, and 0 Resist Composition [0080] The photoresist composition used in the pattern forming process of the invention is typically a chemically ampli?ed positive resist composition. The resist composition used herein comprises a polymer comprising recurring units (a1) and/or (a2) having a carboxyl group and phenolic hydroxyl group Whose hydrogen is substituted by an acid labile group, respectively, as represented by the general for mula (2). (2) Y1 Y2 / a) O I R10 \ \ In formula (2), R9 and R1 l are each independently hydrogen or methyl. R10 and R12 each are an acid labile group. Y1 is a 0 / single bond, a C l-C l2 linking group having at least one ester, lactone ring, phenylene or naphthylene moiety, a phenylene US 2014/0080064 A1 Mar. 20, 2014 13 -continued -continued R9 R9 0 0 OK‘0 O R9 / R 10 i (I O O R10 R10 0 0/ 0 0/ R9 1R9 O O O 0 R10 / O O 0 R10 9 0\h w00 R0 0 0N 0 0 0 \ R m R10 m R m 0/ R/ / US 2014/0080064 A1 Mar. 20, 2014 14 -continued -continued R9 R9 R11 R11 0 0 )YO O O 0 O O R10 ORIZ @ORn 0 O/ i Rll 10 O O/R R9 R9 2Y0O O O ORIZ O O O Herein R1 1 and R12 are as de?ned above. \ R10 [0083] The acid labile groups represented by R10 and R12 in 10 formula (2) may be selected from a variety of such groups. O 0/ R 0 The acid labile groups may be the same or different and R9 preferably include groups of the folloWing formulae (A- l) to (A-3). 0 O (A- 1) O 0 (A-3) R10 0 o/ Herein R9 and R10 are as de?ned above. [0084] In formula (A-l), R30 is a tertiary alkyl group of 4 to [0082] The recurring units (a2) having an acid labile group 20 carbon atoms, preferably 4 to 15 carbon atoms, a trialkyl in formula (2) are recurring units having a phenolic hydroxyl silyl group in Which each alkyl moiety has 1 to 6 carbon group, typically hydroxystyrene or hydroxyphenyl(meth) atoms, an oxoalkyl group of 4 to 20 carbon atoms, or a group acrylate, in Which the hydrogen of its hydroxyl moiety is of formula (A-3). Exemplary tertiary alkyl groups are tert substituted by an acid labile group. Suitable monomers from butyl, tert-amyl, l,l-diethylpropyl, l-ethylcyclopentyl, l-bu Which the recurring units (a2) are derived are illustrated tylcyclopentyl, l -ethylcyclohexyl, l -butylcyclohexyl, beloW. l-ethyl-2-cyclopentenyl, l-ethyl-2-cyclohexenyl, and 2-me thyl-2-adamantyl. Exemplary trialkylsilyl groups are trim R11 ethylsilyl, triethylsilyl, and dimethyl-tert-butylsilyl. Exem R11 plary oxoalkyl groups are 3-oxocyclohexyl, 4-methyl-2 oxooxan-4-yl, and 5-methyl-2-oxooxolan-5-yl. Letter k is an ORIZ integer of 0 to 6. [0085] In formula (A-2), R31 and R32 are hydrogen or straight, branched or cyclic alkyl groups of l to 18 carbon ORlZ atoms, preferably 1 to 10 carbon atoms. Exemplary alkyl ORIZ groups include methyl, ethyl, propyl, isopropyl, n-butyl, sec butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, and US 2014/0080064 A1 Mar. 20, 2014 15 n-octyl. R33 is a monovalent hydrocarbon group of 1 to 18 -continued carbon atoms, preferably 1 to 10 carbon atoms, Which may (A-l )-4 R3 8 contain a heteroatom such as oxygen, examples of Which / include straight, branched or cyclic alkyl groups and substi tuted forms of such alkyl groups in Which some hydrogen atoms are replaced by hydroxyl, alkoxy, oxo, amino, alky lamino or the like. Illustrative examples of the substituted alkyl groups are shoWn beloW. (A-1)-6 T O O R37 [0086] A pair of R31 and R32, R31 and R33, or R32 and R33 may bond together to form a ring With the carbon and oxygen atoms to Which they are attached. Each of R3 l, R32 and R33 is a straight or branched alkylene group of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms When they form a ring, While the ring preferably has 3 to 10 carbon atoms, more preferably 4 to 10 carbon atoms. [0087] Examples of the acid labile groups of formula (A-l) include tert-butoxycarbonyl, tert-butoxycarbonylmethyl, R37 tert-amyloxycarbonyl, tert-amyloxycarbonylmethyl, (CH2)k 0 R37 [0088] 1 ,1 -diethylpropyloxycarbonyl, TW4 0 R37 [0089] 1 ,1 -diethylpropyloxycarbonylmethyl, [0090] 1 -ethylcyclopentyloxycarbonyl, [0091] 1 -ethylcyclopentyloxycarbonylmethyl, [0092] 1 -ethyl-2-cyclopentenyloxycarbonyl, 0 R37 [0093] 1 -ethyl-2-cyclopentenyloxycarbonylmethyl, [0094] 1 -ethoxyethoxycarbonylmethyl, [0095] 2-tetrahydropyranyloxycarbonylmethyl, and (CHZMYOQO [0096] 2-tetrahydrofuranyloxycarbonylmethyl groups. [0097] Also included are sub stituent groups having the for mulae (A-1)-1 to (A-1)-10. [0098] Herein R37 is each independently a straight, branched or cyclic Cl-Cl0 alkyl group or C6-C2O aryl group. (A-1)-1 R38 is hydrogen or a straight, branched or cyclic C l-C 10 alkyl ' R37 group. R39 is each independently a straight, branched or / (CH2)k O R38 cyclic C2-C 10 alkyl group or C6-C2O aryl group. The subscript / \H/ / k is an integer of 0 to 6. O [0099] Of the acid labile groups of formula (A-Z), the 37 (A-1)-2 straight and branched ones are exempli?ed by the folloWing R groups having formulae (A-2)-1 to (A-2)-69. //(CH2)k T O R37 0 R37 _ (A-1)-3 ' R37 / (CH2)k O R38 0 US 2014/0080064 A1 Mar. 20, 2014 -continued 5, and cl is an integer ofl to 7. “A” is a (cl +l)-Valent aliphatic (A-2)-67 or alicyclic saturated hydrocarbon group, aromatic hydrocar CH3 bon group or heterocyclic group having 1 to 50 carbon atoms, —CH—O Which may be separated by a heteroatom or in Which some hydrogen atoms attached to carbon atoms may be substituted by hydroxyl, carboxyl, carbonyl radicals or ?uorine atoms. “B” is %OiOi, iNHCOiOi or iNHCONHi. [0103] Preferably, “A” is selected from divalent to tetrava lent, straight, branched or cyclic Cl-C2O alkylene, alkyltriyl and alkyltetrayl groups, and C6-C3O arylene groups, Which may contain a heteroatom or in Which some hydrogen atoms attached to carbon atoms may be substituted by hydroxyl, H C (A-2)-68 carboxyl, acyl radicals or halogen atoms. The subscript cl is preferably an integer of l to 3. 3 \THZ [0104] The crosslinking acetal groups of formulae (A-2a) —CH—O and (A-2b) are exempli?ed by the folloWing formulae (A-2) 70 through (A-2)-77. (A-2)-69 H C CH3 3 \CH/ —CH—O CH3 CH3 [0100] Of the acid labile groups of formula (A-Z), the cyclic ones are, for example, tetrahydrofuran-2-yl, 2-methyltetrahy drofuran-2-yl, tetrahydropyran-2-yl, and 2-methyltetrahy dropyran-2-yl. [0101] Other examples of acid labile groups include those of the following formula (A-2a) or (A-2b) While the polymer may be crosslinked Within the molecule or betWeen mol ecules With these acid labile groups. CH3 [0102] Herein R40 and R41 each are hydrogen or a straight, branched or cyclic Cl-C8 alkyl group, or R40 and R41, taken together, may form a ring With the carbon atom to Which they are attached, and R40 and R41 are straight or branched C l-C8 alkylene groups When they form a ring. R42 is a straight, branched or cyclic C 1 -C 10 alkylene group. Each of bl and d1 [0105] In formula (A-3), R34, R35 and R36 each are a is 0 or an integer of l to 10, preferably 0 or an integer of l to monovalent hydrocarbon group, typically a straight,