18  US 8,114,570 B2  17  and methyl amyl ketone; alcohols such as 3-methoxybutanol,  3-methyl-3-methoxybutanol,  l-methoxy-2-propanol,  and  l-ethoxy-2-propanol; ethers such as  propylene glycol  monomethyl ether, ethylene glycol monomethyl ether, pro- pylene glycol monoethyl ether, ethylene glycol monoethyl  ether, propylene glycol dimethyl ether, and diethylene glycol  dimethyl ether; esters such as propylene glycol monomethyl  ether acetate (PGMEA), propylene glycol monoethyl ether  acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl  3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl  acetate, tert-butyl propionate, and propylene glycol mono› tert-butyl ether acetate; and lactones such as y-butyrolactone.  These solvents may be used alone or in combinations of two  or more thereof. Of the above organic solvents, it is recom› mended to use diethylene glycol dimethyl ether, l-ethoxy-2- propanol, PGMEA, cyclohexanone and mixtures thereof  because the photoacid generator is most soluble therein.  An appropriate amount of the organic solvent used is 200 to  3,000 parts, especially 400 to 2,000 parts by weight per 100  parts by weight of the base resin.  ComponentC  The base resins used as component (C) or (C’) in the inven› tive compositions include polyhydroxystyrene (PHS), and  copolymers of PHS with styrene, (meth)acrylic acid esters or  other polymerizable olefinic compounds, for KrF excimer  laser resist use; (meth)acrylic acid ester polymers, alternating  copolymers of cycloolefin with maleic anhydride and similar  copolymers further containing vinyl ethers or (meth)acrylic  acid esters, polynorbornene, ring-opening metathesis poly› merized cycloolefins, and hydrogenated ring-opening met› athesis polymerized cycloolefins, for ArF excimer laser resist  use; and fluorinated forms of the foregoing polymers (for both  KrF and ArF laser uses) for F $_{2 }$ excimer laser resist use,  although the base resins are not limited to these polymers.  Understandably, the sulfonium salts and iodonium salts hav› ing polymerizable substituent groups according to the inven- tion may be used as a monomer component in forming the  base resin. Typical sulfonium and iodonium salts for such use  are combinations of onium cations such as ( 4-acryloylox› yphenyl)diphenylsulfonium,  (4-methacryloyloxyphenyl)  dipheny lsulfonium, ( 4-acryloy loxypheny 1 )pheny liodonium,  and  ( 4-methacryloyloxyphenyl)phenyliodonium  cations  with anions such as 1-( difluorosulfomethyl)-2,2,2-trifluoro› ethyl hydrogen cyclohexanedicarboxylate. The base resins  may be used alone or in admixture of two or more. In the case  of positive resist compositions, it is a common practice to  substitute acid labile groups for hydroxyl groups on phenols,  carboxyl groups or fluorinated alkyl alcohols for reducing the  rate of dissolution in unexposed regions.  The base resin (C) may comprise recurring units contain- ing an acid labile group of the general formula (3) and recur› ring units of at least one type having the general formulae ( 4)  to (6), shown below.  With respect to the synthesis of imide and oxime sul› fonates, reference should be made to JP-A 2003-252855, U.S.  Pat. No. 6,261,738, JP-A 9-95479, JP-A 9-208554, JP-A  9-230588, JP 2906999, JP-A 9-301948, JP-A 2000-314956,  JP-A 2001-233842, and WO 2004/074242.  As described above, a first embodiment of the invention  provides photoacid generators suited for use in chemically  amplified resist compositions which generate sulfonic acids  of formula (la) upon exposure to high-energy radiation. A  second embodiment provides sulfonium salts, iodonium  salts, dicarboxylimide sulfonates, and oxime sulfonates serv› ing as photoacid generators in chemically amplified resist  compositions. A third embodiment provides chemically  amplified resist compositions comprising a photoacid gen› erator which generates a sulfonic acid of formula (1 a) upon  exposure to high-energy radiation and a resin which changes  its solubility in an alkaline developer liquid under the action  of acid.  The resist composition of the invention is typically embod- ied as  (i) a chemically amplified positive resist composition com› prising  (A) the above-mentioned photoacid generator, i.e., the  photoacid generator capable of generating a sulfonic acid  having formula (1 a), especially the compound of formula (2),  (2a ), (2b ), (3a) or (3b ),  (B) an organic solvent,  (C) a base resin which changes its solubility in an alkaline  developer under the action of acid, and  one or more optional components including (D) a  quencher, (E) a photoacid generator other than (A), (F) an  organic acid derivative and/or fluorinated alcohol, and (G) a  dissolution inhibitor having a weight average molecular  weight ofup to 3,000, and further optionally, (S) a surfactant  which is insoluble or substantially insoluble in water and  soluble in alkaline developer and/or a surfactant which is  insoluble or substantially insoluble in water and alkaline  developer; and  (ii) a chemically amplified negative resist composition com- prising  (A) the above-mentioned photoacid generator,  (B) an organic solvent,  (C’) a base resin which is normally alkali soluble, but  becomes substantially alkali insoluble under the action of a  crosslinker,  (H) a crosslinker which induces crosslinkage under the  action of acid, and  one or more optional components including (D) a quencher  and (E) a photoacid generator other than (A), and further  optionally, (S) a surfactant which is insoluble or substantially  insoluble in water and soluble in alkaline developer and/or a  surfactant which is insoluble or substantially insoluble in  water and alkaline developer.  The PAG which generates a sulfonic acid having formula  (la) as component (A) is as described above. More specifi› cally, it is a compound having formula (2), (2a), (2b ), (3a) or  (3b ). In the resist composition, the PAG is specifically com› pounded in an amount of0.1 to 10 parts, more specifically 1  to 7 parts by weight per 100 parts by weight of the base resin.  Note that parts by weight per 100 parts by weight of the resin  is often abbreviated as "phr."  The organic solvent used herein may be any organic sol› vent in which the base resin, acid generator, and other com- ponents are soluble. Illustrative, non-limiting, examples of  the organic solvent include ketones such as cyclohexanone  H  R 11  (++)  (3)  i  Fa  $^{0 }$\ $_{XA }$ Resist Composition  ComponentB 