US 10,698,314 B2  3  4  -continued  experiences no film thickness loss after development, and  has a high sensitivity, minimized LWR and improved CDU.  In one aspect, the invention provides a chemically ampli› fied resist composition comprising a quencher containing a  quaternary ammonium salt selected from the group consist- ing of a quaternary ammonium iodide, quaternary ammo› nium dibromoiodide, quaternary ammonium bromodiiodide,  and quaternary ammonium triiodide, and an acid generator.  In one preferred embodiment, the quaternary ammonium  salt has the formula (1) or (2).  Herein R 1  to R 4  and R 5  to R$^{10 }$are each independently a  C 1  -C 24  straight, branched or cyclic alkyl group,  C 2 -C 24  straight, branched or cyclic alkenyl group, C 2 -C 24  straight,  branched or cyclic alkynyl group, or  CcC$_{24 }$ aryl group,  which may contain a halogen, hydroxyl, carboxyl, ether,  ester, thiol, thioester, thionoester, dithioester, amino, nitro,  sulfone or ferrocenyl moiety, a pair ofR 1  and R 2 , R 1  and R 4 ,  R 2  and R 3 , and/or R 3  and R 4  may bond together to form a  ring, or a pair ofR 1  and R 2 , R 1  and R 4 , R 2  and R 4 , or R 3  and  R 4 , taken together, may form a double bond, R 11  is a C 2 -C$_{12 }$ straight, branched or cyclic alkylene group which may  contain an ether and/or ester moiety,  x- is an anion selected  from the group consisting of  1-,  Br  2 1-,  Brl 2  - and  1 3  - .  In one preferred embodiment, the acid generator is  capable of generating sulfonic acid, imidic acid or methide  acid.  The resist composition may further comprise a base  polymer.  In owe preferred embodiment, the base polymer com› prises recurring units of at least one type selected from  recurring units having the formulae (fl) to (f3).  Herein  RA  is each independently hydrogen or methyl. Z 1  is  a single bond, phenylene,  ---O-Z 11 -,  or ----C(=0)› Z12-Z11-,  Z 11  is a C 1 -C 6  straight, branched or cyclic  alkylene group or C 2 -C 6  straight, branched or cyclic alk- enylene group which may contain a carbonyl, ester, ether or  hydroxyl moiety, or phenylene group, Z 12  is ---0- or  -NH- Rs1 Rs2 Rs3 Rs4  Rss  Rs6 Rs7 and Rss are each  independent!; a  cl  -c:2  st;aight, br~nch;d or cyclic alkyl  group which may contain a carbonyl, ester or ether moiety,  or a  CcC$_{12 }$ aryl,  C 7 -C$_{20 }$ aralkyl, or mercaptophenyl group.  Z 2  is a single bond, -Z 21 -C(O)O-, -Z 21 -0-, or  -Z 21 -0----C(=0)-, Z 21  is a C 1 -C$_{12 }$straight, branched or  cyclic alkylene group which may contain a carbonyl, ester or  ether moiety. Z 3  is a single bond, methylene, ethylene,  phenylene,  fluorinated  phenylene,  ---O-Z 31 -,  or  ----C(=0)-Z$^{32}$-Z 31 -, Z $^{31 }$is a C 1 -C 6  straight, branched  or cyclic alkylene group or C 2 -C 6  straight, branched or  cyclic alkenylene group which may contain a carbonyl,  ester, ether or hydroxyl moiety, or a phenylene, fluorinated  phenylene or trifluoromethyl-substituted phenylene group,  Z 32  is ---0- or -NH-. A  1  is hydrogen or trifluoromethyl,  and  M- is a non-nucleophilic counter ion.  In one preferred embodiment, the acid generator also  functions as a base polymer. In this case, the acid generator  is a polymer comprising recurring units of at least one type  selected from recurring units having the formulae (fl) to (f3)  defined above.  In one preferred embodiment, the base polymer comprises  recurring units having the formula (al) or recurring units  having the formula (a2).  (fl)  (f2)  (al)  (a2)  ~  OR22  Herein  RA  is each independently hydrogen or methyl, R 11  and R 12  are each independently an acid labile group, X 1  is a  single bond, phenylene, naphthylene, or a $^{C}$1 -C$_{12 }$ linking  group containing ester moiety or lactone ring, and X 2  is a  single bond or ester group.  (fJ) 