ONIUM SALT, CHEMICALLY AMPLIFIED POSITIVE RESIST COMPOSITION, AND RESIST PATTERN FORMING PROCESS

Abstract

The onium salt is capable of generating an acid having an adequate acid strength and low diffusion, a chemically amplified positive resist composition comprising the onium salt, and a resist pattern forming process using the composition. The alkanesulfone type onium salt whose anion has a bulky substituent at ?-position of a sulfo group and a bulky aromatic ring structure is capable of generating an acid having an adequate acid strength and controlled diffusion. A chemically amplified positive resist composition comprising the onium salt is provided.

Claims

1. An onium salt having the formula (A): ##STR00398## wherein n1 is an integer of 0 to 2, n2 is an integer of 2 to 5 in case of n1=0, an integer of 2 to 7 in case of n1=1, and an integer of 2 to 9 in case of n1=2, L is a single bond, ether bond, ester bond, sulfonic ester bond, carbonate bond or carbamate bond, R.sup.1 and R.sup.2 are each independently hydrogen or a C.sub.3-C.sub.20 branched or cyclic hydrocarbyl group which may contain a heteroatom, excluding that both R.sup.1 and R.sup.2 are hydrogen, R.sup.1 and R.sup.2 may bond together to form a ring with the carbon atom to which they are attached, R.sup.3 is each independently iodine or a C.sub.3-C.sub.20 branched or cyclic hydrocarbyl group which may contain a heteroatom, at least one R.sup.3 is attached to a carbon atom adjoining the carbon atom to which L is attached, and Z.sup.+ is an onium cation.

2. The onium salt of claim 1 having the formula (A1): ##STR00399## wherein L, R.sup.1, R.sup.2, R.sup.3, and Z.sup.+ are as defined above, and n3 is an integer of 1 to 4.

3. The onium salt of claim 2 having the formula (A2): ##STR00400## wherein n3, R.sup.1, R.sup.2, R.sup.3, and Z.sup.+ are as defined above.

4. The onium salt of claim 1 wherein Z.sup.+ is an onium cation having the formula (cation-1) or (cation-2): ##STR00401## wherein R.sup.ct1 to R.sup.ct5 are each independently a C.sub.1-C.sub.30 hydrocarbyl group which may contain a heteroatom, and R.sup.ct1 and R.sup.ct2 may bond together to form a ring with the sulfur atom to which they are attached.

5. A photoacid generator comprising the onium salt of claim 1.

6. A chemically amplified positive resist composition comprising the photoacid generator of claim 5.

7. The chemically amplified positive resist composition of claim 6, further comprising a base polymer containing a polymer which is decomposed under the action of acid to increase its solubility in alkaline developer.

8. The chemically amplified positive resist composition of claim 7 wherein the polymer comprises repeat units having the formula (B1): ##STR00402## wherein a1 is 0 or 1, a2 is an integer of 0 to 2, a3 is an integer satisfying 0?a3?5+2(a2)?a4, a4 is an integer of 1 to 3, R.sup.A is hydrogen, fluorine, methyl or trifluoromethyl, R.sup.11 is halogen, an optionally halogenated C.sub.2-C.sub.8 saturated hydrocarbylcarbonyloxy group, optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyl group, or optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyloxy group, and A.sup.1 is a single bond or C.sub.1-C.sub.10 saturated hydrocarbylene group in which some constituent CH.sub.2 may be replaced by O.

9. The chemically amplified positive resist composition of claim 7 wherein the polymer further comprises repeat units having the formula (B2-1): ##STR00403## wherein b1 is 0 or 1, b2 is an integer of 0 to 2, b3 is an integer satisfying 0 b3 5+2(b2)?b4, b4 is an integer of 1 to 3, b5 is 0 or 1, R.sup.A is hydrogen, fluorine, methyl or trifluoromethyl, R.sup.12 is halogen, an optionally halogenated C.sub.2-C.sub.8 saturated hydrocarbylcarbonyloxy group, optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyl group, or optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyloxy group, A.sup.2 is a single bond or C.sub.1-C.sub.10 saturated hydrocarbylene group in which some constituent CH.sub.2 may be replaced by O, X is an acid labile group when b4 is 1, and X is each independently hydrogen or an acid labile group, at least one being an acid labile group, when b4 is 2 or 3.

10. The chemically amplified positive resist composition of claim 7 wherein the polymer further comprises repeat units having the formula (B2-2): ##STR00404## wherein c1 is an integer of 0 to 2, c2 is an integer of 0 to 2, c3 is an integer of 0 to 5, c4 is an integer of 0 to 2, R.sup.A is hydrogen, fluorine, methyl or trifluoromethyl, R.sup.13 and R.sup.14 are each independently a C.sub.1-C.sub.10 hydrocarbyl group which may contain a heteroatom, R.sup.13 and R.sup.14 may bond together to form a ring with the carbon atom to which they are attached, R.sup.15 is each independently fluorine, C.sub.1-C.sub.5 fluorinated alkyl group or C.sub.1-C.sub.5 fluorinated alkoxy group, R.sup.16 is each independently a C.sub.1-C.sub.10 hydrocarbyl group which may contain a heteroatom, and A.sup.3 is a single bond, phenylene group, naphthylene group, or *C(?O)O-A.sup.31-, wherein A.sup.31 is a C.sub.1-C.sub.20 aliphatic hydrocarbylene group which may contain hydroxy, ether bond, ester bond or lactone ring, or a phenylene or naphthylene group, * designates a point of attachment to the carbon atom in the backbone.

11. The chemically amplified positive resist composition of claim 7 wherein the polymer further comprises repeat units of at least one type selected from repeat units having the formula (B3), repeat units having the formula (B4), and repeat units having the formula (B5): ##STR00405## wherein d is an integer of 0 to 6, e is an integer of 0 to 4, f1 is 0 or 1, f2 is an integer of 0 to 2, and f3 is an integer of 0 to 5, R.sup.A is hydrogen, fluorine, methyl or trifluoromethyl, R.sup.17 and R.sup.18 are each independently hydroxy, halogen, an optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyl group, optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyloxy group, or optionally halogenated C.sub.2-C.sub.8 saturated hydrocarbylcarbonyloxy group, R.sup.19 is a C.sub.1-C.sub.20 saturated hydrocarbyl group, C.sub.1-C.sub.20 saturated hydrocarbyloxy group, C.sub.2-C.sub.20 saturated hydrocarbylcarbonyloxy group, C.sub.2-C.sub.20 saturated hydrocarbyloxyhydrocarbyl group, C.sub.2-C.sub.20 saturated hydrocarbylthiohydrocarbyl group, halogen, nitro group, or cyano group, R.sup.19 may be a hydroxy group when f2 is 1 or 2, and A.sup.4 is a single bond or C.sub.1-C.sub.10 saturated hydrocarbylene group in which some constituent CH.sub.2 may be replaced by O.

12. The chemically amplified positive resist composition of claim 7 wherein the polymer further comprises repeat units of at least one type selected from repeat units having the formulae (B6) to (B13): ##STR00406## ##STR00407## wherein R.sup.A is each independently hydrogen, fluorine, methyl or trifluoromethyl, Y.sup.1 is a single bond, a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene group, naphthylene group or C.sub.7-C.sub.18 group obtained by combining the foregoing, *OY.sup.11, *C(?O)OY.sup.11, or *C(?O)NHY.sup.11, Y.sup.11 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene group, naphthylene group or C.sub.7-C.sub.18 group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond or hydroxy moiety, Y.sup.2 is a single bond or **Y.sup.21C(?O)O, Y.sup.21 is a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom, Y.sup.3 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, trifluoromethyl-substituted phenylene, *OY.sup.31, *C(?O)OY.sup.31, or *C(?O)NHY.sup.31, Y.sup.31 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene group, fluorinated phenylene group, trifluoromethyl-substituted phenylene group, or C.sub.7-C.sub.20 group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond or hydroxy moiety, * designates a point of attachment to the carbon atom in the backbone, ** designates a point of attachment to the oxygen in the formula, Y.sup.4 is a single bond or C.sub.1-C.sub.30 hydrocarbylene group which may contain a heteroatom, g1 and g2 are each independently 0 or 1, g1 and g2 are 0 when Y.sup.4 is a single bond, R.sup.21 to R.sup.38 are each independently halogen or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, R.sup.21 and R.sup.22 may bond together to form a ring with the sulfur atom to which they are attached, R.sup.23 and R.sup.24, R.sup.26 and R.sup.27, or R.sup.29 and R.sup.30 may bond together to form a ring with the sulfur atom to which they are attached, R.sup.HF is hydrogen or trifluoromethyl, and Xa.sup.? is a non-nucleophilic counter ion.

13. The chemically amplified positive resist composition of claim 7, further comprising an organic solvent.

14. The chemically amplified positive resist composition of claim 7, further comprising a fluorinated polymer comprising repeat units of at least one type selected from repeat units having the formula (D1), repeat units having the formula (D2), repeat units having the formula (D3) and repeat units having the formula (D4) and optionally repeat units of at least one type selected from repeat units having the formula (D5) and repeat units having the formula (D6): ##STR00408## wherein x is an integer of 1 to 3, y is an integer satisfying 0?y?5+2z?x, z is 0 or 1, h is an integer of 1 to 3, R.sup.B is each independently hydrogen, fluorine, methyl or trifluoromethyl, R.sup.C is each independently hydrogen or methyl, R.sup.101, R.sup.102, R.sup.104 and R.sup.105 are each independently hydrogen or a C.sub.1-C.sub.10 saturated hydrocarbyl group, R.sup.103, R.sup.106, R.sup.107 and R.sup.108 are each independently hydrogen, a C.sub.1-C.sub.15 hydrocarbyl group, C.sub.1-C.sub.15 fluorinated hydrocarbyl group, or acid labile group, and when R.sup.103, R.sup.106, R.sup.107 and R.sup.108 each are a hydrocarbyl or fluorinated hydrocarbyl group, an ether bond or carbonyl moiety may intervene in a carbon-carbon bond, R.sup.109 is hydrogen or a C.sub.1-C.sub.5 straight or branched hydrocarbyl group in which a heteroatom-containing moiety may intervene in a carbon-carbon bond, R.sup.110 is a C.sub.1-C.sub.5 straight or branched hydrocarbyl group in which a heteroatom-containing moiety may intervene in a carbon-carbon bond, R.sup.111 is a C.sub.1-C.sub.20 saturated hydrocarbyl group in which at least one hydrogen is substituted by fluorine, and in which some constituent CH.sub.2 may be replaced by an ester bond or ether bond, Z.sup.1 is a C.sub.1-C.sub.20 (h+1)-valent hydrocarbon group or C.sub.1-C.sub.20 (h+1)-valent fluorinated hydrocarbon group, Z.sup.2 is a single bond, *C(?O)O or *C(?O)NH, * designates a point of attachment to the carbon atom in the backbone, Z.sup.3 is a single bond, O, *C(?O)?OZ.sup.31Z.sup.32 or *C(?O)NHZ.sup.31Z.sup.32, Z.sup.31 is a single bond or C.sub.1-C.sub.10 saturated hydrocarbylene group, Z.sup.32 is a single bond, ester bond, ether bond, or sulfonamide bond, and * designates a point of attachment to the carbon atom in the backbone.

15. The chemically amplified positive resist composition of claim 7, further comprising a quencher.

16. The chemically amplified positive resist composition of claim 7, further comprising a photoacid generator other than the photoacid generator.

17. A resist pattern forming process comprising the steps of: applying the chemically amplified positive resist composition of claim 7 onto a substrate to form a resist film thereon, exposing the resist film to high-energy radiation, and developing the exposed resist film in an alkaline developer.

18. The process of claim 17 wherein the high-energy radiation is EUV or EB.

19. The process of claim 17 wherein the substrate has the outermost surface of a chromium-containing material.

20. The process of claim 17 wherein the substrate is a photomask blank.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0089] As used herein, the singular forms a, an and the include plural referents unless the context clearly dictates otherwise. 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. The notation (Cn-Cm) means a group containing from n to m carbon atoms per group. In chemical formulae, the broken line () and asterisk (*) each designate a point of attachment, namely valence bond. Me stands for methyl and Ac for acetyl. As used herein, the term fluorinated refers to a fluorine-substituted or fluorine-containing compound or group. The terms group and moiety are interchangeable.

[0090] The abbreviations and acronyms have the following meaning. [0091] PAG: photoacid generator [0092] Mw: weight average molecular weight [0093] Mn: number average molecular weight [0094] Mw/Mn: molecular weight distribution or dispersity [0095] GPC: gel permeation chromatography [0096] PEB: post-exposure baking [0097] LER: line edge roughness [0098] CDU: critical dimension uniformity

[0099] It is understood that for some structures represented by chemical formulae, there can exist enantiomers and diastereomers because of the presence of asymmetric carbon atoms. In such a case, a single formula collectively represents all such isomers. The isomers may be used alone or in admixture.

Onium Salt

[0100] One embodiment of the invention is an onium salt having the formula (A).

##STR00012##

[0101] In formula (A), n1 is an integer of 0 to 2. The relevant structure represents a benzene ring in case of n1=0, a naphthalene ring in case of n1=1, and an anthracene ring in case of n1=2. From the aspect of solvent solubility, a benzene ring corresponding to n1=0 is preferred. The subscript n2 is an integer of 2 to 5 in case of n1=0, an integer of 2 to 7 in case of n1=1, and an integer of 2 to 9 in case of n1=2.

[0102] In formula (A), L is a single bond, ether bond, ester bond, sulfonic ester bond, carbonate bond or carbamate bond. Inter alia, an ester bond and sulfonic ester bond are preferred, with sulfonic ester bond being more preferred.

[0103] In formula (A), R.sup.1 and R.sup.2 are each independently hydrogen or a C.sub.3-C.sub.20 branched or cyclic hydrocarbyl group which may contain a heteroatom, excluding that both R.sup.1 and R.sup.2 are hydrogen. When both R.sup.1 and R.sup.2 are hydrogen or a straight hydrocarbyl group, the structure in proximity to SO.sub.3.sup.? group becomes less bulky, suggesting that apparent acid diffusion is not restrained and lithography performance is degraded.

[0104] The hydrocarbyl groups R.sup.1 and R.sup.2 may be saturated or unsaturated. Examples thereof include, but are not limited to, C.sub.3-C.sub.20 branched alkyl groups such as isopropyl, sec-butyl, tert-butyl, tert-pentyl, and 2-ethylhexyl; C.sub.3-C.sub.20 cyclic aliphatic hydrocarbyl groups such as cyclopentyl, cyclohexyl, cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl, norbornyl, oxanorbornyl, tricyclo[5.2.1.0.sup.2,6]decyl, and adamantyl; C.sub.6-C.sub.20 aryl groups such as phenyl, naphthyl and anthracenyl, and combinations thereof. In the hydrocarbyl group, some or all of the hydrogen atoms may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, and some constituent CH.sub.2 may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain a hydroxy moiety, cyano moiety, fluorine, chlorine, bromine, iodine, carbonyl moiety, ether bond, ester bond, sulfonic ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (C(?O)OC(?O)) or haloalkyl moiety. Suitable halogen atoms include fluorine, chlorine, bromine, and iodine, with fluorine and iodine being preferred.

[0105] R.sup.1 and R.sup.2 may bond together to form a ring with the carbon atom to which they are attached. Examples of the ring include cyclopropane, cyclobutane, cyclopentane, cyclohexane, norbornane, and adamantane rings. In the ring, some or all of the hydrogen atoms may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, and some constituent CH.sub.2 may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the ring may contain a hydroxy moiety, cyano moiety, fluorine, chlorine, bromine, iodine, carbonyl moiety, ether bond, ester bond, sulfonic ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (C(?O)OC(?O)) or haloalkyl moiety.

[0106] In formula (A), R.sup.3 is each independently iodine or a C.sub.3-C.sub.20 branched or cyclic hydrocarbyl group which may contain a heteroatom. At least one R.sup.3 is attached to a carbon atom adjoining the carbon atom to which L is attached. Examples of the hydrocarbyl group are as exemplified above for the hydrocarbyl groups R.sup.1 and R.sup.2.

[0107] Examples of the structure that R.sup.3 forms with the aromatic ring in formula (A) are shown below, but not limited thereto. Herein, the broken line designates a point of attachment to L.

##STR00013## ##STR00014## ##STR00015## ##STR00016## ##STR00017## ##STR00018## ##STR00019## ##STR00020## ##STR00021## ##STR00022## ##STR00023## ##STR00024## ##STR00025## ##STR00026## ##STR00027## ##STR00028##

[0108] Preferably, the onium salt of formula (A) has the formula (A1).

##STR00029##

[0109] Herein L, R.sup.1, R.sup.2, R.sup.3, and Z.sup.+ are as defined above, and n3 is an integer of 1 to 4.

[0110] More preferably, the onium salt of formula (A1) has the formula (A2).

##STR00030##

[0111] Herein n3, R.sup.1, R.sup.2, R.sup.3, and Z.sup.+ are as defined above.

[0112] Preferred examples of the anion in the onium salt having formula (A) are shown below, but not limited thereto.

##STR00031## ##STR00032## ##STR00033## ##STR00034## ##STR00035## ##STR00036## ##STR00037## ##STR00038## ##STR00039## ##STR00040## ##STR00041## ##STR00042## ##STR00043## ##STR00044## ##STR00045## ##STR00046## ##STR00047## ##STR00048## ##STR00049## ##STR00050##

##STR00051## ##STR00052## ##STR00053## ##STR00054## ##STR00055## ##STR00056## ##STR00057## ##STR00058## ##STR00059## ##STR00060## ##STR00061## ##STR00062## ##STR00063## ##STR00064## ##STR00065## ##STR00066## ##STR00067## ##STR00068## ##STR00069## ##STR00070## ##STR00071## ##STR00072## ##STR00073## ##STR00074## ##STR00075## ##STR00076## ##STR00077## ##STR00078## ##STR00079## ##STR00080## ##STR00081## ##STR00082## ##STR00083## ##STR00084## ##STR00085## ##STR00086## ##STR00087## ##STR00088##

##STR00089## ##STR00090## ##STR00091## ##STR00092## ##STR00093## ##STR00094## ##STR00095## ##STR00096## ##STR00097## ##STR00098## ##STR00099## ##STR00100## ##STR00101## ##STR00102## ##STR00103## ##STR00104## ##STR00105## ##STR00106## ##STR00107## ##STR00108## ##STR00109## ##STR00110## ##STR00111## ##STR00112## ##STR00113## ##STR00114## ##STR00115## ##STR00116## ##STR00117## ##STR00118## ##STR00119## ##STR00120## ##STR00121## ##STR00122## ##STR00123## ##STR00124##

##STR00125## ##STR00126## ##STR00127## ##STR00128## ##STR00129## ##STR00130## ##STR00131## ##STR00132## ##STR00133## ##STR00134## ##STR00135## ##STR00136## ##STR00137## ##STR00138## ##STR00139## ##STR00140## ##STR00141## ##STR00142## ##STR00143## ##STR00144## ##STR00145## ##STR00146## ##STR00147## ##STR00148## ##STR00149## ##STR00150## ##STR00151## ##STR00152## ##STR00153## ##STR00154## ##STR00155## ##STR00156## ##STR00157## ##STR00158## ##STR00159## ##STR00160## ##STR00161## ##STR00162## ##STR00163## ##STR00164## ##STR00165## ##STR00166## ##STR00167## ##STR00168## ##STR00169## ##STR00170## ##STR00171## ##STR00172##

##STR00173## ##STR00174## ##STR00175## ##STR00176## ##STR00177## ##STR00178## ##STR00179## ##STR00180## ##STR00181## ##STR00182## ##STR00183## ##STR00184## ##STR00185## ##STR00186## ##STR00187## ##STR00188## ##STR00189## ##STR00190## ##STR00191## ##STR00192## ##STR00193## ##STR00194## ##STR00195## ##STR00196## ##STR00197## ##STR00198## ##STR00199## ##STR00200## ##STR00201## ##STR00202## ##STR00203## ##STR00204## ##STR00205## ##STR00206## ##STR00207## ##STR00208## ##STR00209## ##STR00210##

[0113] In formula (A), Z.sup.+ is an onium cation. The preferred onium cation is a sulfonium cation having the formula (cation-1) or iodonium cation having the formula (cation-2).

##STR00211##

[0114] In formulae (cation-1) and (cation-2), R.sup.ct1 to R.sup.ct5 are each independently halogen or a C.sub.1-C.sub.30 hydrocarbyl group which may contain a heteroatom.

[0115] Suitable halogen atoms include fluorine, chlorine, bromine and iodine.

[0116] The hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C.sub.1-C.sub.30 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and tert-butyl; C.sub.3-C.sub.30 cyclic saturated hydrocarbyl groups such as cyclopropyl, cyclopentyl, cyclohexyl, cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl, and adamantyl; C.sub.2-C.sub.30 alkenyl groups such as vinyl, allyl, propenyl, butenyl, and hexenyl; C.sub.3-C.sub.30 cyclic unsaturated hydrocarbyl groups such as cyclohexenyl; C.sub.6-C.sub.30 aryl groups such as phenyl, naphthyl and thienyl; C.sub.7-C.sub.30 aralkyl groups such as benzyl, 1-phenylethyl and 2-phenylethyl, and combinations thereof. Inter alia, aryl groups are preferred. In the hydrocarbyl group, some or all of the hydrogen atoms may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen and some constituent CH.sub.2 may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain a hydroxy, cyano, fluorine, chlorine, bromine, iodine, carbonyl, ether bond, ester bond, sulfonic ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (C(?O)OC(?O)), or haloalkyl moiety.

[0117] Also, R.sup.ct1 and R.sup.ct2 may bond together to form a ring with the sulfur atom to which they are attached. Examples of the sulfonium cation having formula (cation-1) wherein R.sup.ct1 and R.sup.ct2 form a ring are shown below.

##STR00212##

[0118] Herein the broken line designates a point of attachment to R.sup.ct3.

[0119] Examples of the sulfonium cation having formula (cation-1) are shown below, but not limited thereto.

##STR00213## ##STR00214## ##STR00215## ##STR00216## ##STR00217## ##STR00218## ##STR00219##

##STR00220## ##STR00221## ##STR00222## ##STR00223## ##STR00224## ##STR00225## ##STR00226## ##STR00227## ##STR00228## ##STR00229## ##STR00230## ##STR00231## ##STR00232## ##STR00233## ##STR00234## ##STR00235## ##STR00236##

##STR00237## ##STR00238## ##STR00239## ##STR00240## ##STR00241## ##STR00242## ##STR00243## ##STR00244## ##STR00245## ##STR00246## ##STR00247## ##STR00248## ##STR00249## ##STR00250## ##STR00251## ##STR00252## ##STR00253## ##STR00254## ##STR00255## ##STR00256## ##STR00257##

[0120] Examples of the iodonium cation having formula (cation-2) are shown below, but not limited thereto.

##STR00258## ##STR00259## ##STR00260## ##STR00261##

[0121] Specific structures of the onium salt include arbitrary combinations of the anion with the cation, both as exemplified above.

[0122] The onium salt is synthesized by any well-known methods. For example, it is described how to prepare an onium salt having formula (A) wherein L is a sulfonic ester bond, that is, the following formula (A).

##STR00262##

[0123] Herein n1, n2, R.sup.1, R.sup.2, R.sup.3, and Z.sup.+ are as defined above, M.sup.+ is a lithium, sodium or potassium ion, and X.sup.? is a halide ion or methylsulfate ion.

[0124] The first step is to react sulfonic acid chloride (S-1) with hydroxysulfonic acid salt (S-2) to form sulfonic acid salt (S-3). The reaction may be conducted in a standard way, typically by sequentially or simultaneously adding sulfonic acid chloride (S-1), hydroxysulfonic acid salt (S-2), and a base to a solvent, and optionally cooling or heating.

[0125] Examples of the solvent which can be used in the first step include water; ethers such as tetrahydrofuran (THF), diethyl ether, diisopropyl ether, di-n-butyl ether and 1,4-dioxane; hydrocarbons such as n-hexane, n-heptane, benzene, toluene, and xylene; aprotic polar solvents such as acetonitrile, dimethyl sulfoxide (DMSO), and N,N-dimethylformamide (DMF); and chlorine organic solvents such as methylene chloride, chloroform and carbon tetrachloride. A suitable solvent may be chosen from these solvents in accordance with reaction conditions while the solvents may be used alone or in admixture.

[0126] Examples of the base which can be used in the first step include ammonia; amines such as triethylamine, pyridine, lutidine, collidine, and N,N-dimethylaniline; hydroxides such as sodium hydroxide, potassium hydroxide, and tetramethylammonium hydroxide; and carbonates such as potassium carbonate and sodium hydrogencarbonate. These bases may be used alone or in admixture.

[0127] The second step is ion exchange reaction between sulfonic acid salt (S-3) and onium salt (S-4) to form onium salt (A). The sulfonic acid salt (S-3) may be one obtained through the first step, ordinary aqueous work-up, and isolation, whereas the reaction product obtained at the end of reaction may be used without post-treatment.

[0128] When sulfonic acid salt (S-3) as isolated is used, the desired onium salt (A) is obtained by dissolving sulfonic acid salt (S-3) in a solvent, mixing the solution with onium salt (S-4), and optionally cooling or heating the reaction mixture. Examples of the solvent include water; ethers such as THF, diethyl ether, diisopropyl ether, di-n-butyl ether and 1,4-dioxane; hydrocarbons such as n-hexane, n-heptane, benzene, toluene, and xylene; aprotic polar solvents such as acetonitrile, DMSO, and DMF; and chlorine organic solvents such as methylene chloride, chloroform and carbon tetrachloride. Finally, the onium salt (A) is recovered from the reaction mixture through ordinary aqueous workup. If necessary, the salt may be purified by a standard technique such as distillation, recrystallization or chromatography.

[0129] When the reaction product obtained at the end of reaction is used without post-treatment, the desired onium salt (A) is obtained by adding onium salt (S-4) to the reaction mixture in which the reaction to synthesize sulfonic acid salt (S-3) is terminated, and optionally cooling or heating the reaction mixture. In this step, there may be added a solvent, examples of which include water; ethers such as THF, diethyl ether, diisopropyl ether, di-n-butyl ether and 1,4-dioxane; hydrocarbons such as n-hexane, n-heptane, benzene, toluene, and xylene; aprotic polar solvents such as acetonitrile, DMSO, and DMF; and chlorine organic solvents such as methylene chloride, chloroform and carbon tetrachloride. Finally, the onium salt (A) is recovered from the reaction mixture through ordinary aqueous workup. If necessary, the salt may be purified by a standard technique such as recrystallization or chromatography.

[0130] Since the onium salt having formula (A) is an onium salt of a non-fluorinated sulfonic acid, it generates an acid having an adequate strength upon exposure to high-energy radiation. Since the onium salt has a bulky substituent at ?-position of SO.sub.3 group, the generated sulfonic acid is blocked in its surrounding. Since the onium salt possesses a bulky substituent at ?-position and another bulky substituent on aromatic ring, the rotation of the bond axis of L linking them is restrained by the steric hindrance. Thus, excessive diffusion of the generated acid is restrained. By virtue of the synergy of these effects, the contrast between exposed and unexposed regions is improved, and a small-size pattern with reduced roughness can be formed. In addition, since the onium salt is fully lipophilic, its preparation and handling are easy, and an appropriate dissolution inhibition is displayed in the unexposed region.

[0131] The onium salt effectively functions as a photoacid generator.

Resist Composition

[0132] Another embodiment of the invention is a chemically amplified positive resist composition essentially comprising (A) a photoacid generator in the form of the onium salt having formula (A) defined above.

(A) Photoacid Generator

[0133] In the chemically amplified positive resist composition, the PAG (A) is preferably present in an amount of 0.1 to 40 parts by weight, more preferably 1 to 20 parts by weight per 80 parts by weight of a base polymer (B) to be described later. The range of the PAG ensures that it generates an acid in an amount necessary for the deprotection of acid labile groups and provides for storage stability. The PAG may be used alone or in admixture.

(B) Base Polymer

[0134] In a preferred embodiment, the resist composition further comprises (B) a base polymer containing a polymer which is decomposed under the action of acid to increase its solubility in alkaline developer.

[0135] The polymer preferably comprises repeat units having the following formula (B1). Notably, the unit having formula (B1) is also referred to as unit B 1.

##STR00263##

[0136] In formula (B1), a1 is 0 or 1. The subscript a2 is an integer of 0 to 2. The structure represents a benzene skeleton when a2=0, a naphthalene skeleton when a2=1, and an anthracene skeleton when a2=2. The subscript a3 is an integer satisfying 0?a3?5+2(a2)?a4, and a4 is an integer of 1 to 3. In case of a2=0, preferably a3 is an integer of 0 to 3, and a4 is an integer of 1 to 3. In case of a2=1 or 2, preferably a3 is an integer of 0 to 4, and a4 is an integer of 1 to 3.

[0137] In formula (B1), R.sup.A is hydrogen, fluorine, methyl or trifluoromethyl.

[0138] In formula (B1), R.sup.11 is halogen, an optionally halogenated C.sub.2-C.sub.8 saturated hydrocarbylcarbonyloxy group, optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyl group, or optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyloxy group. The saturated hydrocarbyl group and saturated hydrocarbyl moiety in the saturated hydrocarbyloxy group and saturated hydrocarbylcarbonyloxy group may be straight, branched or cyclic, and examples thereof include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, butyl, pentyl, hexyl, and structural isomers thereof, cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl, and combinations thereof. A carbon count within the upper limit ensures good solubility in alkaline developer. A plurality of R.sup.11 may be identical or different when a3 is 2 or more.

[0139] In formula (B1), A.sup.1 is a single bond or C.sub.1-C.sub.10 saturated hydrocarbylene group in which some constituent CH.sub.2 may be replaced by O. The saturated hydrocarbylene group may be straight, branched or cyclic and examples thereof include C.sub.1-C.sub.10 alkanediyl groups such as methylene, ethane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, and structural isomers thereof; C.sub.3-C.sub.10 cyclic saturated hydrocarbylene groups such as cyclopropanediyl, cyclobutanediyl, cyclopentanediyl, and cyclohexanediyl; and combinations thereof. For the saturated hydrocarbylene group containing an ether bond, in case of a1=1 in formula (B1), the ether bond may be incorporated at any position excluding the position between the ?-carbon and ?-carbon relative to the ester oxygen. In case of a1=0, the atom that bonds with the main chain becomes an ethereal oxygen, and a second ether bond may be incorporated at any position excluding the position between the ?-carbon and ?-carbon relative to that ethereal oxygen. Saturated hydrocarbylene groups having no more than 10 carbon atoms are desirable because of a sufficient solubility in alkaline developer.

[0140] Preferred examples of the repeat units B1 wherein a1=0 and A.sup.1 is a single bond (meaning that the aromatic ring is directly bonded to the main chain of the polymer), that is, repeat units free of a linker: C(?O)O-A.sup.1- include units derived from 3-hydroxystyrene, 4-hydroxystyrene, 5-hydroxy-2-vinylnaphthalene, and 6-hydroxy-2-vinylnaphthalene. Repeat units having the formula (B1-1) are especially preferred.

##STR00264##

[0141] Herein R.sup.A and a4 are as defined above.

[0142] Preferred examples of the repeat units B1 wherein a1=1, that is, having a linker: C(?O)O-A.sup.1- are shown below, but not limited thereto. Herein R.sup.A is as defined above.

##STR00265##

[0143] The content of repeat units B1 is preferably 30 to 90 mol %, more preferably 40 to 85 mol % of the overall repeat units of the polymer. When the polymer further contains repeat units having formula (B3) and/or repeat units having formula (B4), which provide the polymer with higher etch resistance, the repeat units having a phenolic hydroxy group as a substituent, the total content of repeat units B1 and repeat units B3 and/or B4 is preferably in the range. The repeat units B1 may be used alone or in admixture of two or more.

[0144] In a preferred embodiment, the polymer further contains repeat units B2 having an acidic functional group protected with an acid labile group (i.e., repeat units protected with an acid labile group and adapted to turn alkali soluble under the action of acid) in order that the positive resist composition in an exposed region turn soluble in alkaline developer.

[0145] Typical of the repeat unit B2 is a unit having the formula (B2-1), also referred to as repeat unit B2-1.

##STR00266##

[0146] In formula (B2-1), b1 is 0 or 1. The subscript b2 is an integer of 0 to 2. The structure represents a benzene skeleton when b2=0, a naphthalene skeleton when b2=1, and an anthracene skeleton when b2=2. The subscript b3 is an integer meeting 0?b3?5+2(b2)?b4. The subscript b4 is an integer of 1 to 3, and b5 is 0 or 1. When b2=0, preferably b3 is an integer of 0 to 3 and b4 is an integer of 1 to 3. When b2=1 or 2, preferably b3 is an integer of 0 to 4 and b4 is an integer of 1 to 3.

[0147] In formula (B2-1), R.sup.A is hydrogen, fluorine, methyl or trifluoromethyl.

[0148] In formula (B2-1), R.sup.12 is halogen, an optionally halogenated C.sub.2-C.sub.8 saturated hydrocarbylcarbonyloxy group, optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyl group, or optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyloxy group. The saturated hydrocarbyl group and saturated hydrocarbyl moiety in the saturated hydrocarbyloxy group and saturated hydrocarbylcarbonyloxy group may be straight, branched or cyclic, and examples thereof include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, butyl, pentyl, hexyl, and structural isomers thereof, cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl, and combinations thereof. A carbon count within the upper limit ensures good solubility in alkaline developer. A plurality of R.sup.12 may be identical or different when b3 is 2 or more.

[0149] In formula (B2-1), A.sup.2 is a single bond or a C.sub.1-C.sub.10 saturated hydrocarbylene group in which some constituent CH.sub.2 may be replaced by O. The saturated hydrocarbylene group may be straight, branched or cyclic and examples thereof include C.sub.1-C.sub.10 alkanediyl groups such as methylene, ethane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, and structural isomers thereof; C.sub.3-C.sub.10 cyclic saturated hydrocarbylene groups such as cyclopropanediyl, cyclobutanediyl, cyclopentanediyl, and cyclohexanediyl; and combinations thereof. For the saturated hydrocarbylene group containing an ether bond, in case of b1=1 in formula (B2-1), the ether bond may be incorporated at any position excluding the position between the ?-carbon and ?-carbon relative to the ester oxygen. In case of b1=0, the atom that bonds with the main chain becomes an ethereal oxygen, and a second ether bond may be incorporated at any position excluding the position between the ?-carbon and ?-carbon relative to that ethereal oxygen. Saturated hydrocarbylene groups having no more than 10 carbon atoms are desirable because of a sufficient solubility in alkaline developer.

[0150] In formula (B2-1), X is an acid labile group when b4=1, and hydrogen or an acid labile group, at least one X being an acid labile group, when b4=2 or 3. That is, repeat units B2-1 have phenolic hydroxy groups bonded to an aromatic ring, at least one of which is protected with an acid labile group, or repeat units B2-1 have a carboxy group bonded to an aromatic ring, which is protected with an acid labile group. The acid labile group used herein is not particularly limited as long as it is commonly used in a number of well-known chemically amplified resist compositions and eliminated under the action of acid to release an acidic group.

[0151] Typical of the acid labile group is a tertiary saturated hydrocarbyl group. The tertiary saturated hydrocarbyl group is preferably of 4 to 18 carbon atoms because a monomer for use in polymerization is recoverable by distillation.

[0152] The saturated hydrocarbyl group bonded to the tertiary carbon atom in the tertiary saturated hydrocarbyl group is preferably of 1 to 15 carbon atoms. The C.sub.1-C.sub.15 saturated hydrocarbyl group may be straight, branched or cyclic and contain an oxygen-containing functional group such as an ether bond or carbonyl group in its carbon-carbon bond. The saturated hydrocarbyl groups bonded to the tertiary carbon atom may bond together to form a ring with the tertiary carbon atom to which they are attached.

[0153] Examples of the alkyl substituent include methyl, ethyl, propyl, adamantyl, norbornyl, tetrahydrofuran-2-yl, 7-oxanorbornan-2-yl, cyclopentyl, 2-tetrahydrofuryl, tricyclo[5.2.1.0.sup.2,6]decyl, 8-ethyl-8-tricyclo[5.2.1.0.sup.2,6]decyl, 3-methyl-3-tetracyclo[4.4.0.1.sup.2,5.1.sup.7,10,]dodecyl, tetracyclo[4.4.0.1.sup.2,5. 1.sup.7,10]dodecyl, and 3-oxo-1-cyclohexyl.

[0154] Examples of the tertiary saturated hydrocarbyl group include, but are not limited to, tert-butyl, tert-pentyl, 1-ethyl-1-methylpropyl, 1,1-diethylpropyl, 1,1,2-trimethylpropyl, 1-adamantyl-1-methylethyl, 1-methyl-1-(2-norbornyl)ethyl, 1-methyl-1-(tetrahydrofuran-2-yl)ethyl, 1-methyl-1-(7-oxanorbornan-2-yl)ethyl, 1-methylcyclopentyl, 1-ethylcyclopentyl, 1-propylcyclopentyl, 1-cyclopentylcyclopentyl, 1-cyclohexylcyclopentyl, 1-(2-tetrahydrofuryl)cyclopentyl, 1-(7-oxanorbornan-2-yl)cyclopentyl, 1-methylcyclohexyl, 1-ethylcyclohexyl, 1-cyclopentylcyclohexyl, 1-cyclohexylcyclohexyl, 2-methyl-2-norbornyl, 2-ethyl-2-norbornyl, 8-methyl-8-tricyclo[5.2.1.0.sup.2,6]decyl, 8-ethyl-8-tricyclo[5.2.1.0.sup.2,6]decyl, 3-methyl-3-tetracyclo[4.4.0.1.sup.2,5. 1.sup.7,10]dodecyl, 3-ethyl-3-tetracyclo[4.4.0.1.sup.2,5 1.sup.7,10]dodecyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl, 1-methyl-3-oxo-1-cyclohexyl, 1-methyl-1-(tetrahydrofuran-2-yl)ethyl, 5-hydroxy-2-methyl-2-adamantyl, and 5-hydroxy-2-ethyl-2-adamantyl.

[0155] A group having the following formula (B2-1-1) is also suitable as the acid labile group. The group having formula (B2-1-1) is often used as the acid labile group. It is a good choice of the acid labile group that ensures to form a pattern having a relatively rectangular pattern-substrate interface in a consistent manner. An acetal structure is formed when X is a group having formula (B2-1-1).

##STR00267##

[0156] In formula (B2-1-1), R.sup.L1 is hydrogen or a C.sub.1-C.sub.10 saturated hydrocarbyl group. The saturated hydrocarbyl group may be straight, branched or cyclic.

[0157] A choice of R.sup.L1 may depend on the designed sensitivity of labile group to acid. For example, hydrogen is selected when the acid labile group is designed to ensure relatively high stability and to be decomposed with strong acid. A straight alkyl group is selected when the acid labile group is designed to have relatively high reactivity and high sensitivity to pH changes. Although the choice varies with a particular combination of acid generator and quencher in the resist composition, R.sup.L1 is preferably a group in which the carbon in bond with acetal carbon is secondary, when R.sup.L2 is a relatively large alkyl group substituted at the end and the acid labile group is designed to undergo a substantial change of solubility by decomposition. Examples of R.sup.L1 bonded to acetal carbon via secondary carbon include isopropyl, sec-butyl, cyclopentyl, and cyclohexyl, but are not limited thereto.

[0158] In formula (B2-1-1), R.sup.L2 is a C.sub.1-C.sub.30 hydrocarbyl group. The hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Illustrative are C.sub.1-C.sub.30 saturated hydrocarbyl groups and C.sub.6-C.sub.30 aryl groups. R.sup.L2 is preferably a C.sub.1-C.sub.6 hydrocarbyl group for acquiring a higher resolution in forming small-size patterns. When R.sup.L2 is a 6 hydrocarbyl group, the alcohol created after a progress of acid-aided deprotection reaction is water soluble. Then, when a positive pattern is formed using an alkaline developer, the alcohol is dissolved in the developer so that defects remaining in the exposed region are minimized.

[0159] Preferred examples of the group having formula (B2-1-1) are given below, but not limited thereto. Herein RL is as defined above.

##STR00268## ##STR00269##

[0160] Another acid labile group which can be used herein is a phenolic hydroxy group whose hydrogen is substituted by CH.sub.2COO-(tertiary saturated hydrocarbyl group). The tertiary saturated hydrocarbyl group may be the same as the foregoing tertiary saturated hydrocarbyl group used for the protection of a phenolic hydroxy group.

[0161] Another example of repeat unit B2 is a repeat unit having the following formula (B2-2), referred to as repeat unit B2-2. The repeat unit B2-2 which enables to increase the dissolution rate in the exposed region is a useful choice of the acid labile group-containing unit which affords satisfactory performance against line width variations during develop loading.

##STR00270##

[0162] In formula (B2-2), c1 is an integer of 0 to 2, c2 is an integer of 0 to 2, c3 is an integer of 0 to 5, and c4 is an integer of 0 to 2.

[0163] In formula (B2-2), R.sup.A is hydrogen, fluorine, methyl or trifluoromethyl.

[0164] In formula (B2-2), R.sup.13 and R.sup.14 are each independently a C.sub.1-C.sub.10 hydrocarbyl group which may contain a heteroatom. R.sup.13 and R.sup.14 may bond together to form a ring with the carbon atom to which they are attached.

[0165] In formula (B2-2), R.sup.11 is each independently fluorine, C.sub.1-C.sub.5 fluorinated alkyl group or C.sub.1-C.sub.5 fluorinated alkoxy group.

[0166] In formula (B2-2), R.sup.16 is each independently a C.sub.1-C.sub.10 hydrocarbyl group which may contain a heteroatom.

[0167] In formula (B2-2), A.sup.3 is a single bond, phenylene group, naphthylene group, or *C(?O)O-A.sup.3-. A.sup.31 is a C.sub.1-C.sub.20 aliphatic hydrocarbylene group which may contain hydroxy, ether bond, ester bond or lactone ring, or phenylene or naphthylene group, and * is a point of attachment to the carbon atom in the backbone.

[0168] Preferred examples of the repeat unit B2-2 are shown below, but not limited thereto. Herein R.sup.A is as defined above.

##STR00271##

[0169] The content of repeat units B2 is preferably 5 to 95 mol %, more preferably 20 to 80 mol % based on the overall repeat units of the polymer. Each of repeat units B2 may be of one type or a mixture of two or more types.

[0170] In a preferred embodiment, the polymer further comprises repeat units of at least one type selected from units having the formulae (B3), (B4) and (B5). These repeat units are simply referred to as repeat units B3, B4 and B5, respectively.

##STR00272##

[0171] In formulae (B3) and (B4), d is an integer of 0 to 6 and e is an integer of 0 to 4.

[0172] In formulae (B3) and (B4), R.sup.17 and R.sup.18 are each independently hydroxy, halogen, an optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyl group, optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyloxy group, or optionally halogenated C.sub.2-C.sub.8 saturated hydrocarbylcarbonyloxy group. The saturated hydrocarbyl group, saturated hydrocarbyloxy group and saturated hydrocarbylcarbonyloxy group may be straight, branched or cyclic. When d is 2 or more, a plurality of groups R.sup.17 may be identical or different. When e is 2 or more, a plurality of groups R.sup.18 may be identical or different.

[0173] In formula (B5), f1 is 0 or 1. The subscript f2 is an integer of 0 to 2, and the corresponding structure represents a benzene skeleton when f2=0, a naphthalene skeleton when f2=1, and an anthracene skeleton when f2=2. The subscript f3 is an integer of 0 to 5. In case of f2=0, preferably f3 is an integer of 0 to 3. In case of f2=1 or 2, preferably f3 is an integer of 0 to 4.

[0174] In formula (B5), R.sup.A is hydrogen, fluorine, methyl or trifluoromethyl.

[0175] In formula (B5), R.sup.19 is a C.sub.1-C.sub.20 saturated hydrocarbyl group, C.sub.1-C.sub.20 saturated hydrocarbyloxy group, C.sub.2-C.sub.20 saturated hydrocarbylcarbonyloxy group, C.sub.2-C.sub.20 saturated hydrocarbyloxyhydrocarbyl group, C.sub.2-C.sub.20 saturated hydrocarbylthiohydrocarbyl group, halogen atom, nitro group, or cyano group. In case of f2=1 or 2, R.sup.19 may also be hydroxy. The saturated hydrocarbyl group, saturated hydrocarbyloxy group, saturated hydrocarbylcarbonyloxy group, saturated hydrocarbyloxyhydrocarbyl group, and saturated hydrocarbylthiohydrocarbyl group may be straight, branched or cyclic. When f3 is 2 or more, a plurality of groups R.sup.19 may be identical or different.

[0176] In formula (B5), A.sup.4 is a single bond or a C.sub.1-C.sub.10 saturated hydrocarbylene group in which some constituent CH.sub.2 may be replaced by O. The saturated hydrocarbylene group may be straight, branched or cyclic. Examples thereof are as exemplified above for A.sup.1 in formula (B1).

[0177] When repeat units of at least one type selected from repeat units B3 to B5 are incorporated, better performance is obtained because not only the aromatic ring possesses etch resistance, but the cyclic structure incorporated into the main chain also exerts the effect of improving etch resistance and resistance to EB irradiation during pattern inspection step.

[0178] The content of repeat units B3 to B5 is preferably at least 5 mol % based on the overall repeat units of the polymer for obtaining the effect of improving etch resistance. Also, the content of repeat units B3 to B5 is preferably up to 25 mol %, more preferably up to 20 mol % based on the overall repeat units of the polymer. When the relevant units are free of functional groups or have a functional group other than hydroxy, their content of up to 25 mol % is preferred because the risk of forming development defects is eliminated. Each of the repeat units B3 to B5 may be of one type or a combination of plural types.

[0179] It is preferred that the polymer comprise repeat units B1, repeat units B2, and repeat units of at least one type selected from repeat units B3 to B5, because both etch resistance and high resolution are achievable. The total content of these repeat units is preferably at least 60 mol %, more preferably at least 70 mol %, even more preferably at least 80 mol %, most preferably at least 90 mol % based on the overall repeat units of the polymer.

[0180] In another preferred embodiment, the polymer further comprises repeat units of at least one type selected from repeat units having the formula (B6), repeat units having the formula (B7), repeat units having the formula (B8), repeat units having the formula (B9), repeat units having the formula (B10), repeat units having the formula (B11), repeat units having the formula (B12), and repeat units having the formula (B13), shown below. Notably these repeat units are also referred to as repeat units B6 to B13.

##STR00273## ##STR00274##

[0181] In formulae (B6) to (B13), R.sup.A is each independently hydrogen, fluorine, methyl or trifluoromethyl. Y.sup.1 is a single bond, a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene group, naphthylene group or C.sub.7-C.sub.18 group obtained by combining the foregoing, *OY.sup.11, *C(?O)OY.sup.11, or *C(?O)NHY.sup.11, wherein Y.sup.11 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene group, naphthylene group or C.sub.7-C.sub.18 group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond or hydroxy moiety. Y.sup.2 is a single bond or **-Y.sup.21C(?O)O, wherein Y.sup.21 is a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom. Y.sup.3 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, trifluoromethyl-substituted phenylene, *OY.sup.31, *C(?O)OY.sup.31, or *C(?O)NHY.sup.31, wherein Y.sup.31 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene group, fluorinated phenylene group, trifluoromethyl-substituted phenylene group, or C.sub.7-C.sub.20 group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond or hydroxy moiety. The asterisk (*) designates a point of attachment to the carbon atom in the backbone and ** designates a point of attachment to the oxygen atom in the formula. Y.sup.4 is a single bond or C.sub.1-C.sub.30 hydrocarbylene group which may contain a heteroatom, g1 and g2 are each independently 0 or 1, g1 and g2 are 0 when Y.sup.4 is a single bond.

[0182] In formulae (B6) and (B10), Xa.sup.? is a non-nucleophilic counter ion. Examples of the non-nucleophilic counter ion Xa.sup.? are as described in JP-A 2010-113209 and JP-A 2007-145797.

[0183] In formulae (B7) and (B11) wherein Y.sup.2 is Y.sup.21C(?O)O, Y.sup.21 is a hydrocarbylene group which may contain a heteroatom. Illustrative, non-limiting examples of the hydrocarbylene group Y.sup.21 are given below.

##STR00275##

[0184] In formulae (B7) and (B11), R.sup.HF is hydrogen or trifluoromethyl. Examples of the repeat units B7 and B11 wherein R.sup.HF is hydrogen are as described in JP-A 2010-116550. Examples of the repeat units B7 and B11 wherein R.sup.HF is trifluoromethyl are as described in JP-A 2010-077404. Examples of the repeat units B8 and B12 are as described in JP-A 2012-246265 and JP-A 2012-246426.

[0185] The C.sub.1-C.sub.30 hydrocarbylene group which may contain a heteroatom, represented by Y.sup.4, may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C.sub.1-C.sub.30 alkanediyl groups such as methylene, ethane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl, dodecane-1,12-diyl, tridecane-1,13-diyl, tetradecane-1,14-diyl, pentadecane-1,15-diyl, hexadecane-1,16-diyl, and heptadecane-1,17-diyl; C.sub.3-C.sub.30 cyclic saturated hydrocarbylene groups such as cyclopentanediyl, cyclohexanediyl, norbornanediyl and adamantanediyl; C.sub.6-C.sub.30 arylene groups such as phenylene, methylphenylene, ethylphenylene, n-propylphenylene, isopropylphenylene, n-butylphenylene, isobutylphenylene, sec-butylphenylene, tert-butylphenylene, naphthylene, methylnaphthylene, ethylnaphthylene, n-propylnaphthylene, isopropylnaphthylene, n-butylnaphthylene, isobutylnaphthylene, sec-butylnaphthylene, and tert-butylnaphthylene; and combinations thereof.

[0186] In these hydrocarbylene groups, some or all of the hydrogen atoms may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, or some constituent CH.sub.2 may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain a hydroxy, cyano, fluorine, chlorine, bromine, iodine, carbonyl, ether bond, ester bond, sulfonic ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (C(?O)OC(?O)) or haloalkyl moiety.

[0187] The repeat units B9 and B13 are capable of generating an acid having difluoromethyl at ?-position of sulfonyl group upon exposure to high-energy radiation such as UV, deep UV, EB, EUV, X-ray, ?-ray, or synchrotron radiation. The generated acid has an acid strength suitable for inducing deprotection on a polymer comprising repeat units A2. When a polymer comprising repeat units B9 or B13 is used as the base polymer in the resist composition, the movement and diffusion of the generated acid can be adequately controlled.

[0188] A photoacid generator capable of generating an arenesulfonic acid upon exposure to high-energy radiation is commonly used for inducing deprotection to a polymer comprising repeat units protected with an acetal, tertiary alkyl or tert-butoxycarbonyl group. However, when arenesulfonic acid-generating units are incorporated into a polymer with the intention of exerting the desired effects, the polymer is sometimes not dissolvable in a solvent because of its low solvent solubility. Since a polymer having repeat units B9 or B13 is fully lipophilic, its preparation and handling are easy and a resist composition is readily prepared therefrom.

[0189] Preferred examples of the anion in the monomer from which repeat units B9 or B13 are derived are shown below, but not limited thereto.

##STR00276## ##STR00277## ##STR00278## ##STR00279## ##STR00280## ##STR00281##

[0190] In formulae (B6) to (B13), R.sup.21 to R.sup.38 are each independently halogen or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom.

[0191] Suitable halogen atoms include fluorine, chlorine, bromine and iodine.

[0192] The C.sub.1-C.sub.20 hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C.sub.1-C.sub.20 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.20 cyclic saturated hydrocarbyl groups such as cyclopentyl, cyclohexyl, cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl, norbornyl, tricyclo[5.2.1.0.sup.2,6]decyl, adamantyl and adamantylmethyl; and C.sub.6-C.sub.20 aryl groups such as phenyl, naphthyl, and anthracenyl. In the foregoing hydrocarbyl groups, some or all of the hydrogen atoms may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, and some constituent CH.sub.2 may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain a hydroxy, fluorine, chlorine, bromine, iodine, cyano, nitro, carbonyl, ether bond, ester bond, sulfonic ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (C(?O)OC(?O)) or haloalkyl moiety.

[0193] Also, R.sup.21 and R.sup.22 may bond together to form a ring with the sulfur atom to which they are attached. R.sup.23 and R.sup.24, R.sup.26 and R.sup.27, or R.sup.29 and R.sup.30 may bond together to form a ring with the sulfur atom to which they are attached. Examples of the ring thus formed are as exemplified above for the ring that R.sup.ct1 and R.sup.ct2 in formula (cation-1), taken together, form with the sulfur atom to which they are attached.

[0194] Exemplary structures of the sulfonium cation in formulae (B7) to (B9) are as exemplified above for the sulfonium cation having formula (cation-1), but not limited thereto. Exemplary structures of the iodonium cation in formulae (B11) to (B13) are as exemplified above for the iodonium cation having formula (cation-2), but not limited thereto.

[0195] Of repeat units B6 to B13, repeat units B9 are preferred for the processing of photomask blanks because an optimum acid strength is available from the design of an acid labile group on the polymer.

[0196] The repeat units B6 to B13 are capable of generating an acid upon exposure to high-energy radiation. It is believed that binding of the relevant units to a polymer enables to appropriately control acid diffusion and to form a pattern with reduced LER. Since the acid-generating unit is bound to a polymer, the phenomenon that acid volatilizes from the exposed region and re-deposits on the unexposed region during bake in vacuum is suppressed. This is effective for reducing LER and for suppressing profile degradation due to unwanted film thickness loss in the unexposed region.

[0197] When repeat units B6 to B13 are included, their content is preferably 0.1 to 30 mol %, more preferably 0.5 to 20 mol % based on the overall repeat units of the polymer. Each of repeat units B6 to B13 may be of one type or a combination of plural types.

[0198] The content of repeat units having an aromatic ring structure is preferably at least 65 mol %, more preferably at least 75 mol %, even more preferably at least 85 mol % based on the overall repeat units of the polymer. When the polymer does not contain repeat units B6 to B13, it is preferred that all units have an aromatic ring structure.

[0199] The polymer may further comprise (meth)acrylate units protected with an acid labile group or (meth)acrylate units having an adhesive group such as lactone structure or hydroxy group other than phenolic hydroxy as commonly used in the art. These repeat units are effective for fine adjustment of properties of a resist film, but not essential.

[0200] Examples of the (meth)acrylate unit having an adhesive group include repeat units having the following formulae (B14) to (B16), which are also referred to as repeat units B14 to B16. While these units do not exhibit acidity, they may be used as auxiliary units for providing adhesion to substrates or adjusting solubility.

##STR00282##

[0201] In formulae (B14) to (B16), R.sup.A is each independently hydrogen, fluorine, methyl or trifluoromethyl. R.sup.41 is O or methylene. R.sup.42 is hydrogen or hydroxy. R.sup.43 is a C.sub.1-C.sub.4 saturated hydrocarbyl group, and k is an integer of 0 to 3.

[0202] When repeat units B14 to B16 are included, their content is preferably 0 to 20 mol %, more preferably 0 to 10 mol % based on the overall repeat units of the polymer. Each of repeat units B14 to B16 may be of one type or a combination of plural types.

[0203] The polymer may be synthesized by combining suitable monomers optionally protected with a protective group, copolymerizing them in the standard way, and effecting deprotection reaction if necessary. The copolymerization reaction is preferably radical or anionic polymerization though not limited thereto. For the polymerization reaction, reference may be made to JP-A 2004-115630, for example.

[0204] The polymer should preferably have a Mw of 1,000 to 50,000, and more preferably 2,000 to 20,000. A Mw of at least 1,000 eliminates the risk that pattern features are rounded at their top, inviting degradations of resolution and LER. A Mw of up to 50,000 eliminates the risk that LER is degraded when a pattern with a line width of up to 100 nm is formed. As used herein, Mw is measured by GPC versus polystyrene standards using tetrahydrofuran (THF) or dimethylformamide (DMF) solvent.

[0205] The polymer preferably has a narrow molecular weight distribution or dispersity (Mw/Mn) of 1.0 to 2.0, more preferably 1.0 to 1.9. A polymer with such a narrow dispersity eliminates the risk that foreign particles are left on the pattern after development and the pattern profile is aggravated.

[0206] The base polymer is designed such that the dissolution rate in alkaline developer is preferably up to 10 nm/min, more preferably up to 7 nm/min, even more preferably up to 5 nm/min. In the advanced generation of lithography wherein the coating film on the substrate is in a thin film range of up to 100 nm, the influence of pattern film thickness loss during alkaline development becomes strong. When the polymer has an alkaline dissolution rate of greater than 10 nm/min, pattern collapse occurs, i.e., a small-size pattern cannot be formed. The problem becomes outstanding in the fabrication of photomasks requiring to be defectless and having a tendency of strong development process. It is noted that the dissolution rate of a base polymer in alkaline developer is computed by spin coating a 16.7 wt % solution of a polymer in propylene glycol monomethyl ether acetate (PGMEA) solvent onto a 8-inch silicon wafer, baking at 100? C. for 90 seconds to form a film of 1,000 nm thick, developing the film in a 2.38 wt % aqueous solution of tetramethylammonium hydroxide (TMAH) at 23? C. for 100 seconds, and measuring a loss of film thickness.

[0207] In addition to the polymer defined above, the base polymer (B) may contain another polymer. The other polymer may be any of prior art well-known base polymers used in resist compositions. The content of the other polymer is not particularly limited as long as the benefits of the invention are not impaired.

(C) Organic Solvent

[0208] The chemically amplified positive resist composition may comprise an organic solvent as component (C). The organic solvent used herein is not particularly limited as long as the components are soluble therein. Examples of the organic solvent 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-pentyl ketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, and diacetone alcohol; ethers such as propylene glycol monomethyl ether (PGME), 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 (EL), 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 ?-butyrolactone (GBL), 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 to accelerate deprotection reaction of acetal.

[0209] Of the above organic solvents, it is recommended to use 1-ethoxy-2-propanol, PGMEA, PGME, cyclohexanone, EL, GBL, and mixtures thereof.

[0210] In the resist composition, the organic solvent (C) is preferably used in an amount of 200 to 10,000 parts, more preferably 400 to 5,000 parts by weight per 80 parts by weight of the base polymer (B). The organic solvent may be used alone or in admixture.

(D) Fluorinated Polymer

[0211] The chemically amplified positive resist composition may further comprise a fluorinated polymer for the purposes of enhancing contrast, preventing chemical flare of acid upon exposure to high-energy radiation, preventing mixing of acid from an anti-charging film in the step of coating an anti-charging film-forming material on a resist film, and suppressing unexpected unnecessary pattern degradation. The fluorinated polymer contains repeat units of at least one type selected from repeat units having the formula (D1), repeat units having the formula (D2), repeat units having the formula (D3), and repeat units having the formula (D4), and may contain repeat units of at least one type selected from repeat units having the formula (D5) and repeat units having the formula (D6). It is noted that repeat units having formulae (D1), (D2), (D3), (D4), (D5), and (D6) are also referred to as repeat units D1, D2, D3, D4, D5, and D6, respectively, hereinafter. Since the fluorinated polymer also has a surface active function, it can prevent insoluble residues from re-depositing onto the substrate during the development step and is thus effective for preventing development defects.

##STR00283##

[0212] In formulae (D1) to (D6), x is an integer of 1 to 3, y is an integer satisfying: 0?y?5+2z?x, z is 0 or 1, and h is an integer of 1 to 3. R.sup.B is each independently hydrogen, fluorine, methyl or trifluoromethyl. R.sup.C is each independently hydrogen or methyl. R.sup.101, R.sup.102, R.sup.104 and R.sup.105 are each independently hydrogen or a C.sub.1-C.sub.10 saturated hydrocarbyl group. R.sup.103, R.sup.106, R.sup.107 and R.sup.108 are each independently hydrogen, a C.sub.1-C.sub.15 hydrocarbyl group or fluorinated hydrocarbyl group, or an acid labile group, with the proviso that an ether bond or carbonyl moiety may intervene in a carbon-carbon bond in the hydrocarbyl groups or fluorinated hydrocarbyl groups represented by R.sup.103, R.sup.106, R.sup.107 and R.sup.108. R.sup.109 is hydrogen or a C.sub.1-C.sub.5 straight or branched hydrocarbyl group in which a heteroatom-containing moiety may intervene in a carbon-carbon bond. R.sup.110 is a C.sub.1-C.sub.5 straight or branched hydrocarbyl group in which a heteroatom-containing moiety may intervene in a carbon-carbon bond. R.sup.111 is a C.sub.1-C.sub.20 saturated hydrocarbyl group in which at least one hydrogen is substituted by fluorine and some constituent CH.sub.2 may be replaced by an ester bond or ether bond. Z.sup.1 is a C.sub.1-C.sub.20 (h+1)-valent hydrocarbon group or C.sub.1-C.sub.20 (h+1)-valent fluorinated hydrocarbon group. Z.sup.2 is a single bond, *C(?O)O or *C(?O)NH wherein the asterisk (*) designates a point of attachment to the carbon atom in the backbone. Z.sup.3 is a single bond, O, *C(?O)OZ.sup.31Z.sup.32 or *C(?O)NHZ.sup.31Z.sup.32, wherein Z.sup.31 is a single bond or a C.sub.1-C.sub.10 saturated hydrocarbylene group, Z.sup.32 is a single bond, ester bond, ether bond or sulfonamide bond, and the asterisk (*) designates a point of attachment to the carbon atom in the backbone.

[0213] In formulae (D1) and (D2), the C.sub.1-C.sub.10 saturated hydrocarbyl group represented by R.sup.101, R.sup.102, R.sup.104 and R.sup.105 may be straight, branched or cyclic and 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, n-hexyl, n-heptyl, n-octyl, n-nonyl, and n-decyl, and C.sub.3-C.sub.10 cyclic saturated hydrocarbyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, adamantyl, and norbornyl. Inter alia, C.sub.1-C.sub.6 saturated hydrocarbyl groups are preferred.

[0214] In formulae (D1) to (D4), the C.sub.1-C.sub.15 hydrocarbyl group represented by R.sup.103, R.sup.106, R.sup.107 and R.sup.108 may be straight, branched or cyclic and examples thereof include C.sub.1-C.sub.15 alkyl, C.sub.2-C.sub.15 alkenyl and C.sub.2-C.sub.15 alkynyl groups, with the alkyl groups being preferred. Suitable alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl and n-pentadecyl. The fluorinated hydrocarbyl groups correspond to the foregoing hydrocarbyl groups in which some or all carbon-bonded hydrogen atoms are substituted by fluorine atoms.

[0215] In formula (D4), examples of the C.sub.1-C.sub.20 (h+1)-valent hydrocarbon group Z.sup.1 include the foregoing C.sub.1-C.sub.20 alkyl groups and C.sub.3-C.sub.20 cyclic saturated hydrocarbyl groups, with h number of hydrogen atoms being eliminated. Examples of the C.sub.1-C.sub.20 (h+1)-valent fluorinated hydrocarbon group Z.sup.1 include the foregoing (h+1)-valent hydrocarbon groups in which at least one hydrogen atom is substituted by fluorine.

[0216] Examples of the repeat units D1 to D4 are given below, but not limited thereto. Herein R.sup.B is as defined above.

##STR00284## ##STR00285## ##STR00286##

[0217] In formula (D5), examples of the C.sub.1-C.sub.5 hydrocarbyl groups R.sup.109 and R.sup.110 include alkyl, alkenyl and alkynyl groups, with the alkyl groups being preferred. Suitable alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and n-pentyl. In these groups, a moiety containing a heteroatom such as oxygen, sulfur or nitrogen may intervene in a carbon-carbon bond.

[0218] In formula (D5), OR.sup.109 is preferably a hydrophilic group. In this case, R.sup.109 is preferably hydrogen or a C.sub.1-C.sub.5 alkyl group in which oxygen intervenes in a carbon-carbon bond.

[0219] In formula (D5), Z.sup.2 is preferably *C(?O)O or *C(?O)NH. Also preferably R.sup.C is methyl. The inclusion of carbonyl in Z.sup.2 enhances the ability to trap the acid originating from the anti-charging film. A polymer wherein R.sup.C is methyl is a robust polymer having a high glass transition temperature (Tg) which is effective for suppressing acid diffusion. As a result, the resist film is improved in stability with time, and neither resolution nor pattern profile is degraded.

[0220] Examples of the repeat unit D5 are given below, but not limited thereto. Herein R.sup.C is as defined above.

##STR00287## ##STR00288## ##STR00289##

[0221] In formula (D6), the C.sub.1-C.sub.10 saturated hydrocarbylene group Z.sup.3 may be straight, branched or cyclic and examples thereof include methanediyl, ethane-1,1-diyl, ethane-1,2-diyl, propane-1,1-diyl, propane-1,2-diyl, propane-1,3-diyl, propane-2,2-diyl, butane-1,1-diyl, butane-1,2-diyl, butane-1,3-diyl, butane-2,3-diyl, butane-1,4-diyl, and 1,1-dimethylethane-1,2-diyl.

[0222] The C.sub.1-C.sub.20 saturated hydrocarbyl group having at least one hydrogen substituted by fluorine, represented by R.sup.111, may be straight, branched or cyclic and examples thereof include C.sub.1-C.sub.20 alkyl groups and C.sub.3-C.sub.20 cyclic saturated hydrocarbyl groups in which at least one hydrogen is substituted by fluorine.

[0223] Examples of the repeat unit D6 are given below, but not limited thereto. Herein R.sup.C is as defined above.

##STR00290## ##STR00291## ##STR00292## ##STR00293## ##STR00294##

[0224] The content of repeat units D1 to D4 is preferably 15 to 95 mol %, more preferably 20 to 85 mol % based on the overall repeat units of the fluorinated polymer. The content of repeat unit D5 and/or D6 is preferably 5 to 85 mol %, more preferably 15 to 80 mol % based on the overall repeat units of the fluorinated polymer. Each of repeat units D1 to D6 may be used alone or in admixture.

[0225] The fluorinated polymer may comprise additional repeat units as well as the repeat units D1 to D6. Suitable additional repeat units include those described in U.S. Pat. No. 9,091,918 (JP-A 2014-177407, paragraphs [0046]-[0078]). When the fluorinated polymer comprises additional repeat units, their content is preferably up to 50 mol % based on the overall repeat units.

[0226] The fluorinated polymer may be synthesized by combining suitable monomers optionally protected with a protective group, copolymerizing them in the standard way, and effecting deprotection reaction if necessary. The copolymerization reaction is preferably radical or anionic polymerization though not limited thereto. For the polymerization reaction, reference may be made to JP-A 2004-115630.

[0227] The fluorinated polymer should preferably have a Mw of 2,000 to 50,000, and more preferably 3,000 to 20,000. A fluorinated polymer with a Mw of less than 2,000 helps acid diffusion, degrading resolution and detracting from age stability. A polymer with too high Mw has a reduced solubility in solvent, with a risk of leaving coating defects. The fluorinated polymer preferably has a dispersity (Mw/Mn) of 1.0 to 2.2, more preferably 1.0 to 1.7.

[0228] In the resist composition, the fluorinated polymer (D) is preferably used in an amount of 0.01 to 30 parts by weight, more preferably 0.1 to 20 parts by weight per 80 parts by weight of the base polymer (B). The fluorinated polymer may be used alone or in admixture.

(E) Quencher

[0229] The resist composition may further contain a quencher as component (E). The quencher is a compound having a function of trapping the acid generated by the acid generator. The quencher is effective for holding down the rate of diffusion of the acid (generated by the acid generator) in the resist film. Even when a substrate whose outermost surface is made of a chromium-containing material is used, the quencher is effective for suppressing the influence of the acid (generated in the resist film) on the chromium-containing material.

[0230] One preferred example of the quencher is an onium salt of carboxylic acid having the formula (E1).

R.sup.201CO.sub.2.sup.?Mq.sup.+(E1)

[0231] In formula (E1), R.sup.201 is a C.sub.1-C.sub.40 hydrocarbyl group which may contain a heteroatom. The hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Examples include C.sub.1-C.sub.40 alkyl groups, C.sub.3-C.sub.40 cyclic saturated hydrocarbyl groups, C.sub.2-C.sub.40 alkenyl groups, C.sub.2-C.sub.40 alkynyl groups, C.sub.3-C.sub.40 cyclic unsaturated aliphatic hydrocarbyl groups, C.sub.6-C.sub.40 aryl groups, C.sub.7-C.sub.40 aralkyl groups, and combinations thereof. In the hydrocarbyl group, some or all hydrogen may be substituted by a hydroxy, carboxy, halogen, cyano, amide, nitro, mercapto, sultone, sulfone or sulfonium salt-containing moiety, and some constituent CH.sub.2 may be replaced by an ether bond, ester bond, carbonyl moiety, carbonate moiety or sulfonic ester bond.

[0232] In formula (E1), Mq.sup.+ is an onium cation. Suitable onium cations include sulfonium, iodonium and ammonium cations, with the sulfonium cations being preferred. Preferred sulfonium cations are as exemplified above for the sulfonium cation having formula (cation-1).

[0233] When the resist composition contains the carboxylic onium salt having formula (E1) as the quencher, its content is preferably 0.1 to 40 parts by weight, more preferably 0.1 to 20 parts by weight per 80 parts by weight of the base polymer (B).

[0234] Another preferred example of the quencher is an onium salt of carboxylic acid having the formula (E2) or (E3).

##STR00295##

[0235] Herein, Mq.sup.+ is as defined above.

[0236] In formula (E2), R.sup.211 to R.sup.214 are each independently hydrogen, -L.sup.A-CO.sub.2.sup.?, or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom. A pair of R.sup.211 and R.sup.212, R.sup.212 and R.sup.213, or R.sup.213 and R.sup.214 may bond together to form a ring with the carbon atoms to which they are attached. L.sup.A is a single bond or a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom. R.sup.115 is hydrogen or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom.

[0237] In formula (E2), the ring R is a ring of 2 to 6 carbon atoms including the carbon and nitrogen atoms depicted in the formula, in which some or all of the carbon-bonded hydrogen atoms may be substituted by a C.sub.1-C.sub.20 hydrocarbyl moiety or -L.sup.A-CO.sub.2.sup.?, and some constituent CH.sub.2 may be replaced by a divalent moiety containing sulfur, oxygen or nitrogen. The ring may be alicyclic or aromatic and is preferably 5- or 6-membered. Examples include pyridine, pyrrole, pyrrolidine, piperidine, pyrazole, imidazoline, pyridazine, pyrimidine, pyrazine, imidazoline, oxazole, thiazole, morpholine, thiazine, and triazole rings.

[0238] The carboxylic onium salt having formula (E2) has at least one -L.sup.A-CO.sub.2.sup.? group. That is, at least one of R.sup.211 to R.sup.214 is -L.sup.A-CO.sub.2.sup.? and/or at least one of carbon-bonded hydrogen atoms in the ring R is substituted by -L.sup.A-CO.sub.2.sup.?.

[0239] In formula (E3), R.sup.221 to R.sup.226 are each independently hydrogen or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom. A pair of R.sup.221 and R.sup.222, or R.sup.223 and R.sup.226 may bond together to form a ring with the carbon atoms to which they are attached, and a pair of R.sup.224 and R.sup.225 may bond together to form a ring with the nitrogen atom to which they are attached. The subscript k1 is 0 or 1, and k2 is 0 or 1 in case of k1=0 and k2 is an integer of 0 to 3 in case of k1=1.

[0240] When the resist composition contains the carboxylic onium salt having formula (E2) or (E3) as the quencher, its content is preferably 0.1 to 50 parts by weight, more preferably 0.5 to 30 parts by weight per 80 parts by weight of the base polymer (B).

[0241] A further preferred example of the quencher is a sulfonium compound having the formula (E4).

##STR00296##

[0242] In formula (E4), R.sup.231, R.sup.232 and R.sup.233 are each independently a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom. In the hydrocarbyl group, some hydrogen may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, and some constituent CH.sub.2 may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain a hydroxy moiety, cyano moiety, carbonyl moiety, ether bond, thioether bond, ester bond, sulfonic ester bond, carbonate bond, carbamate bond, lactone ring, sultone ring, carboxylic anhydride (C(?O)OC(?O)) or haloalkyl moiety. The constituent CH.sub.2 in the hydrocarbyl group may be a carbon atom bonded to the benzene ring.

[0243] In formula (E4), z1 and z2 are each independently an integer of 0 to 5, and z3 is an integer of 0 to 4. From the standpoints of ease of synthesis and availability of reactants, z1, z2 and z3 each are preferably 0, 1 or 2.

[0244] When z1 is 2 to 5, two adjoining R.sup.231 may bond together to form a ring with the carbon atoms to which they are attached. When z2 is 2 to 5, two adjoining R.sup.232 may bond together to form a ring with the carbon atoms to which they are attached. When z3 is 2 to 4, two adjoining R.sup.233 may bond together to form a ring with the carbon atoms to which they are attached.

[0245] When the resist composition contains the sulfonium compound having formula (E4) as the quencher, its content is preferably 0.1 to 40 parts by weight, more preferably 1 to 20 parts by weight per 80 parts by weight of the base polymer (B).

[0246] In combination with the above-mentioned onium salt compound, a photo-decomposable onium salt having a nitrogen-containing substituent group may be used as the quencher, if desired. This compound functions as a quencher in the unexposed region, but as a so-called photo-degradable base in the exposed region because it loses the quencher function in the exposed region due to neutralization thereof with the acid generated by itself. Using a photo-degradable base, the contrast between exposed and unexposed regions can be further enhanced. With respect to the photo-degradable base, reference may be made to JP-A 2009-109595, 2012-046501 and JP-A 2013-209360, for example. When the resist composition contains the photo-degradable base as the quencher, its content is preferably 0.1 to 40 parts by weight, more preferably 0.1 to 20 parts by weight per 80 parts by weight of the base polymer (B).

[0247] An amine compound may also be used as the quencher. Suitable amine compounds include primary, secondary and tertiary amine compounds as described in JP-A 2008-111103, paragraphs [0146]-[0164] (U.S. Pat. No. 7,537,880), especially amine compounds having a hydroxy group, ether bond, ester bond, lactone ring, cyano group or sulfonic ester bond. Also useful are compounds having primary or secondary amine protected with a carbamate group, as described in JP 3790649. When the resist composition contains the amine compound as the quencher, its content is preferably 0.001 to 12 parts by weight, more preferably 0.01 to 8 parts by weight per 80 parts by weight of the base polymer (B).

(F) Other Photoacid Generator

[0248] In addition to the PAG in the form of the onium salt having formula (A), the chemically amplified positive resist composition may further comprise another photoacid generator (PAG). The other PAG used herein may be 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.

[0249] Suitable other PAGs include nonafluorobutane sulfonate, partially fluorinated sulfonates described in JP-A 2012-189977, paragraphs [0247]-[0251], partially fluorinated sulfonates described in JP-A 2013-101271, paragraphs [0261]-[0265], and those described in JP-A 2008-111103, paragraphs [0122]-[0142] and JP-A 2010-215608, paragraphs [0080]-[0081]. Among others, arylsulfonate and alkanesulfonate type PAGs are preferred because they generate acids having an appropriate strength to deprotect the acid labile group in repeat unit B2.

[0250] The preferred PAGs are salt compounds having a sulfonium anion of the structure shown below.

##STR00297## ##STR00298## ##STR00299## ##STR00300## ##STR00301## ##STR00302## ##STR00303## ##STR00304## ##STR00305## ##STR00306## ##STR00307## ##STR00308## ##STR00309## ##STR00310## ##STR00311## ##STR00312##

[0251] Also preferred as the PAG is a salt compound containing an anion having the formula (F1).

##STR00313##

[0252] In formula (F1), m1 is 0 or 1, p is an integer of 1 to 3, q is an integer of 1 to 5, and r is an integer of 0 to 3.

[0253] In formula (F1), L.sup.1 is a single bond, ether bond, ester bond, sulfonic ester bond, carbonate bond or carbamate bond.

[0254] In formula (F1), L.sup.2 is an ether bond, ester bond, sulfonic ester bond, carbonate bond or carbamate bond.

[0255] In formula (F1), L.sup.B is a single bond or a C.sub.1-C.sub.20 hydrocarbylene group when p is 1. L.sup.B is a C.sub.1-C.sub.20 (p+1)-valent hydrocarbon group when p is 2 or 3. The hydrocarbylene group and (p+1)-valent hydrocarbon group may contain at least one moiety selected from ether bond, carbonyl moiety, ester bond, amide bond, sultone ring, lactam ring, carbonate bond, halogen, hydroxy moiety and carboxy moiety.

[0256] The C.sub.1-C.sub.20 hydrocarbylene group L.sup.B may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C.sub.1-C.sub.20 alkanediyl groups such as methylene, ethane-1,1-diyl, ethane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl, dodecane-1,12-diyl; C.sub.3-C.sub.20 cyclic saturated hydrocarbylene groups such as cyclopentanediyl, cyclohexanediyl, norbornanediyl and adamantanediyl; C.sub.2-C.sub.20 unsaturated aliphatic hydrocarbylene groups such as vinylene and propene-1,3-diyl; C.sub.6-C.sub.20 arylene groups such as phenylene and naphthylene; and combinations thereof. The C.sub.1-C.sub.20 (p+1)-valent hydrocarbon group L.sup.B may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include those exemplified above for the C.sub.1-C.sub.20 hydrocarbylene group, with one or two hydrogen atoms being eliminated.

[0257] In formula (F1), Rf.sup.1 and Rf.sup.2 are each independently hydrogen, fluorine or trifluoromethyl, at least one being fluorine or trifluoromethyl.

[0258] In formula (F1), R.sup.301 is hydroxy, carboxy, a C.sub.1-C.sub.6 saturated hydrocarbyl group, C.sub.1-C.sub.6 saturated hydrocarbyloxy group, C.sub.2-C.sub.6 saturated hydrocarbylcarbonyloxy group, fluorine, chlorine, bromine, amino, N(R.sup.301A)C(?O)R.sup.301B or N(R.sup.301A)C(?O)OR.sup.301B, R.sup.301A is hydrogen or a C.sub.1-C.sub.6 saturated hydrocarbyl group. R.sup.301B is a C.sub.1-C.sub.6 saturated hydrocarbyl group or C.sub.2-C.sub.8 unsaturated aliphatic hydrocarbyl group.

[0259] The C.sub.1-C.sub.6 saturated hydrocarbyl group represented by R.sup.301, R.sup.301A and R.sup.301B may be straight, branched or cyclic. Examples thereof include C.sub.1-C.sub.6 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, and n-hexyl; and C.sub.3-C.sub.6 cyclic saturated hydrocarbyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl. Examples of the saturated hydrocarbyl moiety in the C.sub.1-C.sub.6 saturated hydrocarbyloxy group represented by R.sup.301 are as exemplified above for the saturated hydrocarbyl group. Examples of the saturated hydrocarbyl moiety in the C.sub.2-C.sub.6 saturated hydrocarbylcarbonyloxy group represented by R.sup.301 are as exemplified above for the C.sub.1-C.sub.6 saturated hydrocarbyl group, but of 1 to 5 carbon atoms.

[0260] The C.sub.2-C.sub.8 unsaturated aliphatic hydrocarbyl group represented by R.sup.301B may be straight, branched or cyclic and examples thereof include C.sub.2-C.sub.8 alkenyl groups such as vinyl, propenyl, butenyl, and hexenyl; C.sub.2-C.sub.8 alkynyl groups such as ethynyl, propynyl, and butynyl; and C.sub.3-C.sub.5 cyclic unsaturated aliphatic hydrocarbyl groups such as cyclohexenyl and norbornenyl.

[0261] In formula (F1), R.sup.302 is a C.sub.1-C.sub.20 saturated hydrocarbylene group or C.sub.6-C.sub.14 arylene group. Some or all of the hydrogen atoms in the saturated hydrocarbylene group may be substituted by halogen other than fluorine. Some or all of the hydrogen atoms in the arylene group may be substituted by a substituent selected from C.sub.1-C.sub.20 saturated hydrocarbyl groups, C.sub.1-C.sub.20 saturated hydrocarbyloxy groups, C.sub.6-C.sub.14 aryl groups, halogen, and hydroxy.

[0262] The C.sub.1-C.sub.20 saturated hydrocarbylene group represented by R.sup.302 may be straight, branched or cyclic. Examples thereof include C.sub.1-C.sub.20 alkanediyl groups such as methylene, ethane-1,1-diyl, ethane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl, dodecane-1,12-diyl; and C.sub.3-C.sub.20 cyclic saturated hydrocarbylene groups such as cyclopentanediyl, cyclohexanediyl, norbornanediyl and adamantanediyl.

[0263] Examples of the C.sub.6-C.sub.14 arylene group represented by R.sup.302 include phenylene, naphthylene, phenanthrenediyl, and anthracenediyl. The C.sub.1-C.sub.20 saturated hydrocarbyl moiety and hydrocarbyl moiety in the C.sub.1-C.sub.20 hydrocarbyloxy moiety, which are substituents on the arylene group, may be straight, branched or cyclic and examples thereof include C.sub.1-C.sub.20 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, heptadecyl, octadecyl, nonadecyl, and icosyl; and C.sub.3-C.sub.20 cyclic saturated hydrocarbyl groups such as cyclopropyl, cyclopentyl, cyclohexyl, cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl and adamantyl. Examples of the C.sub.6-C.sub.14 arylene moiety which is a substituent on the arylene group include phenylene, naphthylene, phenanthrenediyl and anthracenediyl.

[0264] More preferably, the anion has the formula (F2).

##STR00314##

[0265] In formula (F2), p, q, r, L.sup.1, L.sup.B, and R.sup.301 are as defined above. The subscript m2 is an integer of 1 to 4. R.sup.302A is a C.sub.1-C.sub.20 saturated hydrocarbyl group, C.sub.1-C.sub.20 saturated hydrocarbyloxy group, C.sub.6-C.sub.14 aryl group, halogen or hydroxy group. When m2 is 2, 3 or 4, a plurality of R.sup.302A may be identical or different.

[0266] Examples of the anion having formula (F1) are shown below, but not limited thereto.

##STR00315## ##STR00316## ##STR00317## ##STR00318## ##STR00319## ##STR00320## ##STR00321## ##STR00322## ##STR00323## ##STR00324## ##STR00325## ##STR00326## ##STR00327## ##STR00328##

##STR00329## ##STR00330## ##STR00331## ##STR00332## ##STR00333## ##STR00334## ##STR00335## ##STR00336## ##STR00337## ##STR00338## ##STR00339## ##STR00340## ##STR00341## ##STR00342## ##STR00343## ##STR00344## ##STR00345## ##STR00346## ##STR00347## ##STR00348##

##STR00349## ##STR00350## ##STR00351## ##STR00352## ##STR00353## ##STR00354## ##STR00355## ##STR00356## ##STR00357## ##STR00358## ##STR00359## ##STR00360## ##STR00361## ##STR00362##

##STR00363## ##STR00364## ##STR00365## ##STR00366## ##STR00367## ##STR00368## ##STR00369## ##STR00370## ##STR00371## ##STR00372## ##STR00373## ##STR00374## ##STR00375## ##STR00376## ##STR00377## ##STR00378## ##STR00379## ##STR00380## ##STR00381## ##STR00382## ##STR00383## ##STR00384## ##STR00385## ##STR00386##

[0267] Preferred examples of the cation that pairs with the anion include sulfonium and iodonium cations. Examples of the sulfonium cation are as exemplified above for the sulfonium cation having formula (cation-1), but not limited thereto. Examples of the iodonium cation are as exemplified above for the iodonium cation having formula (cation-2), but not limited thereto.

[0268] The other PAG generates an acid having a pKa value of preferably ?2.0 or larger, more preferably ?1.0 or larger. The upper limit of pKa is preferably 2.0. Notably, the pKa value is computed using pKa DB in software ACD/Chemsketch ver: 9.04 of Advanced Chemistry Development Inc.

[0269] When the resist composition contains the other PAG (F), the amount of the PAG (F) used is preferably 1 to 10 parts, more preferably 1 to 5 parts by weight per 80 parts by weight of the base polymer (B). The other PAG may be used alone or in admixture. The inclusion of the other PAG provides for appropriate adjustment of the amount of acid generated in the exposed region and the degree of dissolution inhibition in the unexposed region.

(G) Surfactant

[0270] The resist composition may contain any conventional surfactants for facilitating to coat the composition to the substrate. A number of surfactants are known in the art as described in WO 2006/121096, JP-A 2008-102383, JP-A 2008-304590, JP-A 2004-115630, and JP-A 2005-008766, and any suitable one may be chosen therefrom.

[0271] When the resist composition contains the surfactant (G), the amount of the surfactant (G) added is preferably up to 2 parts by weight, more preferably up to 1 part by weight and preferably at least 0.01 part by weight per 80 parts by weight of the base polymer (B).

Process

[0272] A further embodiment of the invention is a pattern forming process comprising the steps of applying the chemically amplified positive resist composition defined above onto a substrate to form a resist film thereon, exposing the resist film to a pattern of high-energy radiation, and developing the exposed resist film in an alkaline developer.

[0273] The substrate used herein may be selected from, for example, substrates for IC fabrication, e.g., Si, SiO, SiO.sub.2, SiN, SiON, TiN, WSi, BPSG, SOG, and organic antireflective coating, and substrates for mask circuit fabrication, e.g., Cr, CrO, CrON, MoSi.sub.2, Si, SiO, and SiO.sub.2.

[0274] The resist composition is first applied onto a substrate by a suitable coating technique such as spin coating. The coating is prebaked on a hotplate preferably at a temperature of 60 to 150? C. for 1 to 20 minutes, more preferably at 80 to 140? C. for 1 to 10 minutes to form a resist film of 0.03 to 2 ?m thick.

[0275] Then the resist film is exposed patternwise to high-energy radiation. Examples of the high-energy radiation include UV, deep UV, excimer laser radiation (typically, KrF and ArF), EB, EUV, X-ray, ?-ray, and synchrotron radiation.

[0276] On use of UV, deep UV, excimer laser radiation, EUV, X-ray, ?-ray, and synchrotron radiation, the resist film is exposed through a mask having the desired pattern, preferably in a dose of 1 to 300 mJ/cm.sup.2, more preferably 10 to 200 mJ/cm.sup.2. On use of EB, a pattern may be directly written preferably in a dose of 1 to 300 ?C/cm.sup.2, more preferably 10 to 200 ?C/cm.sup.2. The resist composition of the invention is particularly useful in the EUV and EB lithography processes.

[0277] The exposure may be performed by conventional lithography whereas the immersion lithography of holding a liquid, typically water between the resist film and the mask may be employed if desired. In the case of immersion lithography, a protective film which is insoluble in water may be formed on the resist film.

[0278] After the exposure, the resist film may be baked (PEB), for example, on a hotplate preferably at 60 to 150? C. for 1 to 20 minutes, and more preferably at 80 to 140? C. for 1 to 10 minutes.

[0279] Finally, development is carried out using as the developer an aqueous alkaline solution, such as a 0.1 to 5 wt %, preferably 2 to 3 wt %, aqueous solution of tetramethylammonium hydroxide (TMAH), this being done by a conventional method such as dip, puddle, or spray development for a period of 0.1 to 3 minutes, and preferably 0.5 to 2 minutes. In this way the exposed region of resist film is dissolved away, forming the desired pattern on the substrate.

[0280] The resist composition of the invention is advantageous particularly on use under the situation that requires high etching resistance, and a minimal change of pattern line width and minimal LER even when the time duration from exposure to PEB is prolonged. It is also advantageous for pattern formation on a substrate having a surface layer of material to which the resist pattern is less adherent with a likelihood of pattern stripping or pattern collapse, specifically a substrate having sputter deposited thereon a layer of metallic chromium or a chromium compound containing one or more light elements such as oxygen, nitrogen and carbon. The resist composition is particularly useful in forming a pattern on a photomask blank as the substrate.

EXAMPLES

[0281] Examples of the invention are given below by way of illustration and not by way of limitation. The abbreviation pbw is parts by weight. Analysis is made by time-of-flight mass spectrometry (TOF-MS) using an analyzer: MALDI TOF-MS: S3000 by JEOL Ltd.

[1] Synthesis of Onium Salts

Example 1-1 Synthesis of PAG-1

[0282] ##STR00387##

[0283] In nitrogen atmosphere, 10.6 g of SM-1, 6.3 g of SM-2 and 0.3 g of 4-dimethylaminopyridine were suspended in 50 g of THF. The suspension was cooled in an ice bath, after which 3.5 g of triethylamine was added dropwise to the suspension, which was stirred at room temperature for 10 hours. After aging, the reaction solution was cooled down and 50 g of water was added to quench the reaction. Thereafter, 9.4 g of SM-3 was added. The target compound was extracted with 100 g of methylene chloride and subjected to ordinary aqueous workup. The solvent was distilled off, obtaining 15.5 g of PAG-1 as oily matter (yield 73%).

[0284] PAG-1 was analyzed by TOF-MS.

[0285] MALDI TOF-MS: [0286] positive M.sup.+ 277 (corresponding to C.sub.18H.sub.13OS.sup.+) [0287] negative M? 573 (corresponding to C.sub.31H.sub.41O.sub.6S.sup.?)

Examples 1-2 to 1-7 Synthesis of PAG-2 to PAG-7

[0288] Onium Salts PAG-2 to PAG-7, shown below, were synthesized through well-known organic synthesis reaction using the corresponding reactants.

##STR00388## ##STR00389##

[2] Synthesis of Base Polymer

Synthesis Example 1 Synthesis of Polymer P-1

[0289] A 100-ml flask was charged with 20 g of a hydroxystyrene-acenaphthylene copolymer and 46.7 g of THF solvent. In nitrogen atmosphere, 0.5 g of methanesulfonic acid was added to the solution at room temperature (?25? C.), and 4.4 g of 1-methoxy-2-methylpropene was added dropwise thereto, after which reaction ran at room temperature for 4.5 hours. At the end of reaction, 1.0 g of triethylamine was added to the reaction solution, which was added dropwise to 500 g of hexane for precipitation. The solid precipitate was collected by filtration and washed twice with 120 g of hexane. The solid was dissolved in a mixture of 60 g of ethyl acetate and 20 g of water. The solution was transferred to a separatory funnel, to which 0.7 g of acetic acid was added, followed by separatory operation. After the lower layer was removed, 20 g of water and 0.9 g of pyridine were added to the organic layer, followed by separatory operation. After the lower layer was removed, 20 g of water was added to the organic layer, followed by water washing and separatory operation. The water washing and separatory operation was repeated 5 times in total. Thereafter, the organic layer was concentrated and dissolved in 40 g of PGME. The solution was added dropwise to 600 g of water for precipitation. The solid precipitate was collected by filtration, washed with water, and dried, obtaining 20.3 g of the target Polymer P-1 as white solids. Polymer P-1 was analyzed by .sup.1H-NMR, .sup.13C-NMR and GPC, with the analysis results shown below.

##STR00390##

Synthesis Examples 2 to 9 Synthesis of Polymers P-2 to P-9

[0290] Polymers P-2 to P-9 shown below were synthesized with reference to Synthesis Example 1 and the well-known method except that the type and amount (blending ratio) of monomers were changed.

##STR00391## ##STR00392## ##STR00393##

[3] Preparation of Resist Composition

Examples 2-1 to 2-32 and Comparative Examples 1-1 to 1-21

[0291] A chemically amplified positive resist composition was prepared by dissolving selected components in an organic solvent in accordance with the formulation shown in Tables 1 to 3, and filtering the solution through a nylon filter with a pore size of 5 nm and a UPE filter with a pore size of 1 nm. The organic solvent was a mixture of 940 pbw of PGMEA, 1,870 pbw of EL and 1,870 pbw of PGME.

TABLE-US-00001 TABLE 1 Photoacid Fluorinated Resist Polymer 1 Polymer 2 generator Quencher polymer composition (pbw) (pbw) (pbw) (pbw) (pbw) Example 2-1 R-1 P-1 PAG-1 (12) Q-1 D-1 (80) (7.0) (1.5) 2-2 R-2 P-1 PAG-2 (12) Q-1 D-1 (80) (7.0) (1.5) 2-3 R-3 P-1 PAG-3 (12) Q-1 D-1 (80) (7.0) (1.5) 2-4 R-4 P-1 PAG-4 (12) Q-1 D-1 (80) (7.0) (1.5) 2-5 R-5 P-1 PAG-5 (12) Q-1 D-1 (80) (7.0) (1.5) 2-6 R-6 P-1 PAG-6 (12) Q-1 D-1 (80) (7.0) (1.5) 2-7 R-7 P-1 PAG-7 (12) Q-1 D-1 (80) (7.0) (1.5) 2-8 R-8 P-1 PAG-1 (8) Q-2 (80) PAG-A (2) (7.0) 2-9 R-9 P-2 PAG-1 (8) Q-1 D-2 (80) PAG-A (2) (7.0) (1.5) 2-10 R-10 P-2 PAG-4 (8) Q-2 D-1 (80) PAG-A (2) (6.8) (1.5) 2-11 R-11 P-2 PAG-5 (8) Q-4 D-3 (80) PAG-A (2) (7.0) (1.5) 2-12 R-12 P-3 PAG-1 (8) Q-1 D-1 (80) PAG-B (2) (7.0) (1.5) 2-13 R-13 P-3 PAG-2 (8) Q-2 D-4 (80) PAG-A (2) (7.0) (1.5) 2-14 R-14 P-3 PAG-7 (8) Q-3 D-1 (80) PAG-A (2) (7.0) (1.5) 2-15 R-15 P-4 PAG-1 (8) Q-1 D-5 (80) PAG-A (2) (7.0) (1.5) 2-16 R-16 P-4 PAG-4 (8) Q-1 D-2 (80) PAG-A (2) (6.8) (1.5) 2-17 R-17 P-4 PAG-6 (8) Q-3 D-1 (80) PAG-B (2) (7.0) (1.5) 2-18 R-18 P-5 PAG-1 (8) Q-1 D-4 (80) PAG-A (2) (7.0) (1.5) 2-19 R-19 P-5 PAG-2 (8) Q-1 D-1 (80) PAG-A (2) (7.0) (1.5) 2-20 R-20 P-5 PAG-4 (8) Q-2 D-3 (80) PAG-A (2) (7.0) (1.5)

TABLE-US-00002 TABLE 2 Photoacid Fluorinated Resist Polymer 1 Polymer 2 generator Quencher polymer composition (pbw) (pbw) (pbw) (pbw) (pbw) Example 2-21 R-21 P-6 PAG-1 (8) Q-1 D-1 (80) PAG-A (2) (6.6) (1.5) 2-22 R-22 P-6 PAG-4 (8) Q-1 D-2 (80) PAG-A (2) (7.0) (1.5) 2-23 R-23 P-6 PAG-3 (8) Q-4 D-1 (80) PAG-A (2) (7.0) (1.5) 2-24 R-24 P-7 PAG-1 (8) Q-1 D-4 (80) PAG-A (2) (7.0) (1.5) 2-25 R-25 P-7 PAG-5 (8) Q-2 D-1 (80) PAG-B (2) (7.0) (1.5) 2-26 R-26 P-7 PAG-6 (8) Q-3 D-2 (80) PAG-A (2) (7.0) (1.5) 2-27 R-27 P-8 P-1 PAG-1 (5) Q-1 D-3 (40) (40) (7.0) (1.5) 2-28 R-28 P-8 PAG-3 (5) Q-2 D-1 (80) (7.0) (1.5) 2-29 R-29 P-8 P-3 PAG-6 (5) Q-1 D-2 (80) (40) (7.0) (1.5) 2-30 R-30 P-9 PAG-1 (8) Q-1 D-1 (80) PAG-A (2) (7.0) (1.5) 2-31 R-31 P-9 PAG-3 (8) Q-3 D-3 (80) PAG-B (2) (7.0) (1.5) 2-32 R-32 P-9 PAG-6 (8) Q-4 D-1 (80) PAG-A (2) (7.0) (1.5)

TABLE-US-00003 TABLE 3 Photoacid Fluorinated Resist Polymer 1 Polymer 2 generator Quencher polymer composition (pbw) (pbw) (pbw) (pbw) (pbw) Comparative 1-1 CR-1 P-1 cPAG-1 (12) Q-1 D-1 Example (80) (7.0) (1.5) 1-2 CR-2 P-1 cPAG-2 (12) Q-1 D-1 (80) (7.0) (1.5) 1-3 CR-3 P-1 cPAG-3 (12) Q-1 D-1 (80) (7.0) (1.5) 1-4 CR-4 P-1 cPAG-4 (12) Q-1 D-1 (80) (7.0) (1.5) 1-5 CR-5 P-1 cPAG-1 (8) Q-2 (80) PAG-A (2) (7.0) 1-6 CR-6 P-2 cPAG-1 (8) Q-1 D-2 (80) PAG-A (2) (7.0) (1.5) 1-7 CR-7 P-2 cPAG-4 (8) Q-2 D-1 (80) PAG-A (2) (6.8) (1.5) 1-8 CR-8 P-3 cPAG-2 (8) Q-2 D-4 (80) PAG-A (2) (7.0) (1.5) 1-9 CR-9 P-3 cPAG-3 (8) Q-3 D-1 (80) PAG-A (2) (7.0) (1.5) 1-10 CR-10 P-4 cPAG-1 (8) Q-1 D-5 (80) PAG-A (2) (7.0) (1.5) 1-11 CR-11 P-4 cPAG-2 (8) Q-4 D-4 (80 PAG-B (2) (7.0) (1.5) 1-12 CR-12 P-5 cPAG-1 (8) Q-1 D-4 (80) PAG-A (2) (7.0) (1.5) 1-13 CR-13 P-5 cPAG-3 (8) Q-1 D-1 (80) PAG-A (2) (7.0) (1.5) 1-14 CR-14 P-6 cPAG-1 (8) Q-1 D-1 (80) PAG-A (2) (7.0) (1.5) 1-15 CR-15 P-6 cPAG-4 (8) Q-2 D-2 (80) PAG-A (2) (7.0) (1.5) 1-16 CR-16 P-7 cPAG-1 (8) Q-1 D-4 (80) PAG-A (2) (7.0) (1.5) 1-17 CR-17 P-7 cPAG-2 (8) Q-2 D-1 (80) PAG-B (2) (7.0) (1.5) 1-18 CR-18 P-8 P-1 cPAG-1 (5) Q-1 D-3 (40) (40) (7.0) (1.5) 1-19 CR-19 P-8 cPAG-2 (5) Q-2 D-1 (80) (7.0) (1.5) 1-20 CR-20 P-9 cPAG-1 (8) Q-1 D-1 (80) PAG-A (2) (7.0) (1.5) 1-21 CR-21 P-9 cPAG-3 (8) Q-3 D-3 (80) PAG-B (2) (7.0) (1.5)

[0292] Comparative photoacid generators cPAG-1 to cPAG-4, Photoacid generators PAG-A and PAG-B, Quenchers Q-1 to Q-4, and Fluorinated Polymers D-1 to D-5 in Tables 1 to 3 are identified below.

##STR00394## ##STR00395## ##STR00396## ##STR00397##

[4] EB Lithography Test

Examples 3-1 to 3-32 and Comparative Examples 2-1 to 2-21

[0293] A photomask blank of reflection type for an EUV lithography mask was furnished by starting with a low-coefficient-of-thermal-expansion glass substrate of 6 inches squares and depositing thereon a multilayer reflective film of 40 Mo/Si layers with a thickness of 284 nm, a Ru film of 3.5 nm thick as protective film, a TaN film of 70 nm thick as absorbing layer, and a CrN film of 6 nm thick as hard mask. Using a coater/developer system ACT-M (Tokyo Electron Ltd.), each of the resist compositions (R-1 to R-32, CR-1 to CR-21) was spin coated onto the photomask blank, and prebaked on a hotplate at 110? C. for 600 seconds to form a resist film of 80 nm thick. The thickness of the resist film was measured by an optical film thickness measurement system Nanospec (Nanometrics Inc.). Measurement was made at 81 points in the plane of the blank substrate excluding a peripheral band extending 10 mm inward from the blank periphery, and an average film thickness and a film thickness range were computed therefrom.

[0294] The resist film was exposed to EB using an EB writer system EBM-5000Plus (NuFlare Technology Inc., accelerating voltage 50 kV), then baked (PEB) at 110? C. for 600 seconds, and developed in a 2.38 wt % TMAH aqueous solution, thereby yielding a positive pattern.

[0295] The resist pattern was evaluated as follows. The patterned mask blank was observed under a top-down scanning electron microscope (TD-SEM). The optimum dose (Eop) was defined as the exposure dose (?C/cm.sup.2) which provided a 1:1 resolution at the top and bottom of a 200-nm 1:1 line-and-space (LS) pattern. The resolution (or maximum IS resolution) was defined as the minimum size at the dose which provided a 9:1 resolution for an isolated space (IS) of 200 nm. The edge roughness (LER) of a 200-nm LS pattern was measured under SEM. The develop loading was evaluated by forming a 200-nm LS pattern at the dose (?C/cm2) capable of resolving a 1:1 LS pattern of 200 nm design at a ratio 1:1 and a 200-nm LS pattern including dummy patterns having a density of 15%, 25%, 33%, 45%, 50%, 55%, 66%, 75%, 85%, and 95% arranged around the center pattern, measuring the size of spaces under SEM, and comparing the size difference among grouped and isolated patterns. Also, the pattern was visually observed to judge whether or not the profile was rectangular.

[0296] The dissolution rate of an exposed region is computed by spin coating the resist solution onto a 8-inch silicon wafer, baking at 110? C. for 60 seconds to form a resist film of 90 nm thick, exposing the resist film to KrF excimer laser radiation in a dose (mJ/cm.sup.2) capable of resolving a 200-nm 1:1 LS pattern at a ratio 1:1, baking at 110? C. for 60 seconds, developing the film in a 2.38 wt % TMAH aqueous solution at 23? C., and measuring a loss of film thickness by means of a resist development rate analyzer (RDA-800 by Litho Tech Japan Corp.). The results are shown in Tables 4 and 5.

TABLE-US-00004 TABLE 4 Optimum Maximum Develop loading Dissolution Resist dose IS resolution LER variation Pattern rate in exposed composition (?C/cm.sup.2) (nm) (nm) (?nm) profile region (nm/s) Example 3-1 R-1 210 17 4.2 1.8 rectangular 130 3-2 R-2 210 17 4.4 1.8 rectangular 120 3-3 R-3 205 18 4.2 1.7 rectangular 110 3-4 R-4 210 19 4.5 1.6 rectangular 110 3-5 R-5 215 18 4.4 1.7 rectangular 130 3-6 R-6 215 19 4.3 1.8 rectangular 130 3-7 R-7 215 17 4.4 1.7 rectangular 120 3-8 R-8 220 18 4.5 1.8 rectangular 110 3-9 R-9 215 17 4.2 1.7 rectangular 120 3-10 R-10 215 19 4.2 1.8 rectangular 120 3-11 R-11 220 19 4.4 1.7 rectangular 120 3-12 R-12 210 17 4.4 1.8 rectangular 130 3-13 R-13 215 18 4.3 1.8 rectangular 110 3-14 R-14 215 19 4.3 1.7 rectangular 120 3-15 R-15 215 19 4.5 1.7 rectangular 120 3-16 R-16 210 18 4.2 1.8 rectangular 130 3-17 R-17 215 19 4.3 1.7 rectangular 120 3-18 R-18 215 18 4.5 1.8 rectangular 120 3-19 R-19 210 19 4.4 1.7 rectangular 110 3-20 R-20 215 19 4.5 1.8 rectangular 120 3-21 R-21 210 18 4.3 1.7 rectangular 120 3-22 R-22 220 18 4.4 1.8 rectangular 120 3-23 R-23 210 17 4.4 1.7 rectangular 120 3-24 R-24 215 18 4.4 1.8 rectangular 120 3-25 R-25 210 17 4.3 1.8 rectangular 110 3-26 R-26 210 18 4.2 1.7 rectangular 130 3-27 R-27 215 19 4.3 1.7 rectangular 120 3-28 R-28 205 18 4.5 1.8 rectangular 130 3-29 R-29 210 19 4.3 1.7 rectangular 130 3-30 R-30 210 18 4.4 1.8 rectangular 120 3-31 R-31 210 18 4.4 1.7 rectangular 100 3-32 R-32 215 18 4.3 1.8 rectangular 110

TABLE-US-00005 TABLE 5 Optimum Maximum Develop loading Dissolution Resist dose IS resolution LER variation Pattern rate in exposed composition (?C/cm.sup.2) (nm) (nm) (?nm) profile region (nm/s) Comparative 2-1 CR-1 190 22 5 2.2 footing 100 Example 2-2 CR-2 195 23 4.9 2.1 footing 90 2-3 CR-3 200 22 5.1 2 footing 90 2-4 CR-4 200 21 4.8 2.3 footing 80 2-5 CR-5 205 24 5.1 2.4 footing 100 2-6 CR-6 210 23 5 2.1 footing 90 2-7 CR-7 200 22 4.9 2.1 footing 80 2-8 CR-8 210 23 4.8 2.2 footing 90 2-9 CR-9 210 24 5.1 2.4 footing 100 2-10 CR-10 210 23 5.1 2.3 footing 90 2-11 CR-11 205 24 5 2.1 footing 100 2-12 CR-12 210 22 4.8 2.1 footing 90 2-13 CR-13 210 23 4.7 2.1 footing 90 2-14 CR-14 210 24 4.9 2.1 footing 80 2-15 CR-15 215 24 5 2.3 footing 100 2-16 CR-16 210 25 5.1 2 footing 100 2-17 CR-17 215 24 4.9 2.1 footing 90 2-18 CR-18 195 23 4.9 2.4 footing 80 2-19 CR-19 210 24 5.1 2 footing 100 2-20 CR-20 210 24 5 2.3 footing 90 2-21 CR-21 205 24 5.1 2.2 footing 100

[0297] As is evident from Tables 4 and 5, the photoacid generator, the chemically amplified positive resist composition and the resist pattern forming process are effective in photolithography for the fabrication of semiconductor devices and the processing of photomask blanks of transmission and reflection types.

[0298] Japanese Patent Application No. 2023-051139 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.