Photoacid generator, resist composition, and patterning process

1. A photoacid generator for chemically amplified resist compositions which generates a sulfonic acid in response to high-energy radiation selected from UV, deep-UV, EUV, electron beam, x-ray, excimer laser, gamma-ray and synchrotron radiation, said sulfonic acid having the general formula (1a) or (1b):

R 1 —COOCH 2 CF 2 SO 3 − H +   (1a)

R 1 —O—COOCH 2 CF 2 SO 3 − H +   (1b)

wherein R 1 is a monovalent C 20 -C 50 hydrocarbon group of steroid structure which may contain a heteroatom.

2. The photoacid generator of claim 1 which generates a sulfonic acid having the following structural formula (1c) or (1d):

wherein Z is an oxygen atom or —O—(CH 2 ) L —COO—, and L is an integer of 1 to 5.

3. A sulfonium salt having the general formula (2a) or (2b):

R 1 —COOCH 2 CF 2 SO 3 − R 2 R 3 R 4 S +   (2a)

R 1 —O—COOCH 2 CF 2 SO 3 − R 2 R 3 R 4 S +   (2b)

wherein R 1 is a monovalent C 20 -C 50 hydrocarbon group of steroid structure which may contain a heteroatom, R 2 , R 3 and R 4 are each independently a substituted or unsubstituted, straight or branched C 1 -C 10 alkyl, alkenyl or oxoalkyl group or a substituted or unsubstituted C 6 -C 18 aryl, aralkyl or aryloxoalkyl group, or at least two of R 2 , R 3 and R 4 may bond together to form a ring with the sulfur atom.

4. A sulfonium salt having the general formula (3a) or (3b):

R 1 —COOCH 2 CF 2 SO 3 − (R 5 (O) n ) m Ph′S + Ph 2   (3a)

R 1 —O—COOCH 2 CF 2 SO 3 − (R 5 (O) n ) m Ph′S + Ph 2   (3b)

wherein R 1 is a monovalent C 20 -C 50 hydrocarbon group of steroid structure which may contain a heteroatom, R 5 is a substituted or unsubstituted, straight, branched or cyclic C 1 -C 20 alkyl or alkenyl group or a substituted or unsubstituted C 6 -C 14 aryl group, m is an integer of 1 to 5, n is 0 or 1, Ph denotes phenyl, and Ph′ denotes a phenyl group in which a number “m” of hydrogen atoms are substituted by R 5 (O) n — groups.

5. A iodonium salt having the general formula (4a) or (4b):

R 1 —COOCH 2 CF 2 SO 3 − ((R 5 (O) n ) m Ph′) 2 I +   (4a)

R 1 —O—COOCH 2 CF 2 SO 3 − ((R 5 (O) n ) m Ph′) 2 I +   (4b)

wherein R 1 is a monovalent C 20 -C 50 hydrocarbon group of steroid structure which may contain a heteroatom, R 5 is a substituted or unsubstituted, straight, branched or cyclic C 1 -C 20 alkyl or alkenyl group or a substituted or unsubstituted C 6 -C 14 aryl group, m is an integer of 1 to 5, n is 0 or 1, and Ph′ denotes a phenyl group in which a number “m” of hydrogen atoms are substituted by R 5 (O) n — groups.

6. A resist composition comprising a base resin, an acid generator, and an organic solvent, said acid generator comprising a photoacid generator which generates a sulfonic acid having formula (1a) or (1b) as set forth in claim 1 .

7. A resist composition comprising a base resin, an acid generator, and an organic solvent, said acid generator comprising a photoacid generator which generates a sulfonic acid having the following structural formula (1c) or (1d) as set forth in claim 2 ,

wherein Z is an oxygen atom or —O—(CH 2 ) L —COO—, and L is an integer of 1 to 5.

8. The resist composition of claim 6 , wherein said base resin is one or more polymers selected from the group consisting of poly(meth)acrylic acid and derivatives thereof, cycloolefin derivative/maleic anhydride alternating copolymers, copolymers of ternary or more components comprising a cycloolefin derivative, maleic anhydride, and polyacrylic acid or derivatives thereof, cycloolefin derivative/α-trifluoromethyl acrylate derivative copolymers, polynorbornene, ROMP polymers, and hydrogenated ROMP polymers.

9. The resist composition of claim 6 , wherein said base resin is a polymeric structure containing silicon atoms.

10. The resist composition of claim 6 , wherein said base resin is a polymeric structure containing fluorine atoms.

11. The resist composition of claim 6 , wherein said base resin is a polymer comprising recurring units of the general formula (8) and/or (12) and recurring units of at least one type selected from the general formulae (9) to (11), (13), and (14):

wherein R 11 is hydrogen, fluorine, methyl or trifluoromethyl, R 12 and R 13 are each independently hydrogen or hydroxyl, XA is an acid labile group, YL is a substituent group of lactone structure, ZA is hydrogen, C 1 -C 15 fluoroalkyl or C 1 -C 15 fluoroalcohol-containing substituent group,

wherein R 11 and XA are as defined above, and G is an oxygen atom or carboxyl group (—C(═O)O—).

12. A chemically amplified positive resist composition comprising a base resin as set forth in claim 8 , a photoacid generator which generates a sulfonic acid having formula (1a) or (1b) as set forth in claim 1 , and a solvent, wherein said base resin is insoluble or substantially insoluble in a developer, and becomes soluble under the action of the acid.

13. A chemically amplified positive resist composition comprising a base resin as set forth in claim 8 , a photoacid generator which generates a sulfonic acid having formula (1c) or (1d) as set forth in claim 2 , and a solvent, wherein said base resin is insoluble or substantially insoluble in a developer, and becomes soluble under the action of the acid.

14. The chemically amplified positive resist composition of claim 12 , further comprising a quencher.

15. The chemically amplified positive resist composition of claim 12 , further comprising a dissolution inhibitor.

16. A process for forming a pattern comprising the steps of:

applying the resist composition of claim 6 onto a substrate to form a coating,

heat treating the coating and exposing it to high-energy radiation having a wavelength of up to 300 nm through a photomask, and

optionally heat treating and developing the exposed coating with a developer.

17. The process of claim 16 , wherein the exposing step relies on immersion lithography comprising directing radiation from an ArF excimer laser having a wavelength of 193 nm through a projection lens, with a liquid such as water, glycerol or ethylene glycol intervening between the coated substrate and the projection lens.