content_image/915728.jpg content_image/915740.jpg content_image/915741.jpg content_image/915742.jpg content_image/915743.jpg content_image/915744.jpg content_image/915729.jpg content_image/915730.jpg
boxy!, ether bond, ester bond, sulfonic acid ester bond, carbonate bond, lactone ring, sultone ring and carbox› ylic anhydride. 

6. The resist composition of claim 4, further comprising a photoacid generator other than the onium salt. 

7. The resist composition of claim 6 wherein the other photoacid generator has the formula ( 4) or (5): 

<img src='content_image/915728.jpg'>

wherein R 100 , R 200 and R 300 are each independently a straight, branched or cyclic C$_{1 }$-C$_{20 }$ monovalent hydro› carbon group which may contain a heteroatom, any two or more of R 100 , R $^{200 }$and R$^{300 }$may bond together to form a ring with the sulfur atom to which they are attached, x- is an anion selected from the formulae (4A) to (4D): 

<img src='content_image/915740.jpg'>

<img src='content_image/915741.jpg'>

<img src='content_image/915742.jpg'>

<img src='content_image/915743.jpg'>

wherein R: 1 \ R:11’1, R:11’ 2 , R’c1, R’c 2 and R’c3 are each independently fluorine or a straight, branched or cyclic C$_{1 }$-C$_{40 }$ monovalent hydrocarbon group which may contain a heteroatom, or a pair ofR:11’$^{1 }$and R:11’ 2 , or R’c1 and R’c 2 may bond together to form a ring with the carbon atom to which they are attached and any inter› vening atoms, R’d is a straight, branched or cyclic C$_{1 }$-C$_{40 }$ monovalent hydrocarbon group which may contain a heteroatom, 

<img src='content_image/915744.jpg'>

wherein R$^{400 }$and R$^{500 }$are each independently a straight, branched or cyclic C$_{1 }$-C$_{30 }$ monovalent hydrocarbon 

group which may contain a heteroatom, R 600 is a straight, branched or cyclic C$_{1 }$-C$_{30 }$ divalent hydrocar› bon group which may contain a heteroatom, any two or more ofR 400 , R $^{500 }$and R$^{600 }$may bond together to form a ring with the sulfur atom to which they are attached, L is a single bond or a straight, branched or cyclic C$_{1 }$-C$_{20 }$ divalent hydrocarbon group which may contain a heteroatom, X 1 , X 2 , X 3 and X 4 are each indepen› dently hydrogen, fluorine or trifluoromethyl, with the proviso that at least one of X1, X 2 , X 3 and X 4 is a substituent group other than hydrogen. 

8. The resist composition of claim 4, further comprising an amine compound. 

9. The resist composition of claim 4, further comprising a compound having the formula (6) or (7): 

<img src='content_image/915729.jpg'>

<img src='content_image/915730.jpg'>

wherein R 151 , R 152 and R 153 are each independently hydrogen, halogen exclusive of fluorine, or a straight, branched or cyclic C$_{1 }$-C$_{40 }$ monovalent hydrocarbon group which may contain a heteroatom, any two or more ofR 151 , R $^{152 }$and R $^{153 }$may bond together to form a ring with the carbon atom to which they are attached, R $^{154 }$is a straight, branched or cyclic C$_{1 }$-C$_{40 }$monova› lent hydrocarbon group which may contain a heteroa› tom, and M+ is an onium cation. 

10. The resist composition of claim 4, further comprising 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. 

11. A pattern forming process comprising the steps of applying the resist composition of claim 4 onto a substrate, pre baking to form a resist film, exposing a selected region of the resist film to KrF excimer laser, ArF excimer laser, EB or EUV, baking, and developing the exposed resist film in a developer. 

12. The pattern forming process of claim 11 wherein the developing step uses an alkaline aqueous solution as the developer, thereby forming a positive pattern in which an exposed region of the resist film is dissolved away and an unexposed region of the resist film is not dissolved. 

13. The pattern forming process of claim 11 wherein the developing step uses an organic solvent as the developer, thereby forming a negative pattern in which an unexposed region of the resist film is dissolved away and an exposed region of the resist film is not dissolved. 

14. The pattern forming process of claim 13 wherein the organic solvent is at least one solvent selected from the group consisting of 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone, methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, butenyl acetate, isopentyl acetate, propyl formate, butyl formate, isobutyl formate, pentyl formate, isopentyl formate, methyl valerate, methyl pen› tenoate, methyl crotonate, ethyl crotonate, methyl propi› onate, ethyl propionate, ethyl 3-ethoxypropionate, methyl 

