108  US 9,665,002 B2  107  RIOO  I  x- s+-R3oo  (4)  I  R200  wherein R 100 , R 200 , and R $^{300 }$are as defined above, x- is  an anion of any one of the general formulae (5) to (8):  (5)  Rfi’ 1  -CF2-S02  ’N› Rfi’2  -cF$_{2}$-so;  (6)  (7)  (S) wherein  R: 1 \  R:11’1, R:11’ 2 , R’c1, R’c 2 , and R’c3 are each  independently fluorine or a straight C$_{1 }$-C$_{40 }$or branched  or cyclic C$_{3}$-C$_{40 }$monovalent hydrocarbon group which  may be substituted with or separated by a heteroatom,  R:11’ 1  and R:11’ 2 ,  or R’c1 and R’c 2  may bond together to 40  form a ring with the segments to which they are  attached,  R’d  is a straight C$_{1 }$-C$_{40 }$or branched or cyclic  C$_{3}$-C$_{40 }$ monovalent hydrocarbon group which may be  substituted with or separated by a heteroatom.  5.  The resist composition of claim  2,  further comprising  a nonionic nitrogen-containing compound.  *  *  *  *  *  6.  The resist composition of claim  2,  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.  7.  A pattern forming process comprising the steps of  applying the resist composition of claim  2  onto a substrate,  prebaking to form a resist film, exposing the resist film to  KrF excimer laser, ArF excimer laser, EB or EUV through  a photomask, baking, and developing the exposed resist film  in a developer.  8.  The pattern forming process of claim  7  wherein the  exposing step is by immersion lithography wherein a liquid  having a refractive index of at least 1.0 is interposed  between the resist film and a projection lens.  9.  The pattern forming process of claim  8,  further com› prising the step of forming a protective film on the resist  film, and in the immersion lithography, the liquid is inter› posed between the protective film and the projection lens.  10.  The onium salt compound of claim  1  wherein R$^{44 }$and  R$^{55 }$bond together to form a ring with the nitrogen atom to  which they are attached, and the ring may have an oxygen  atom, sulfur atom or NH moiety interposed therein.  11.  The onium salt compound of claim  10  wherein the ring  is selected from the group consisting of the following  structures: 