Nov.  17, 2016  25  US 2016/0334706 Al  0  OH  0  [{Yo  ~’  v::;?  y  ’so,  0  F2  0  C  (o  Y’so,  -continued  -continued  [0086]  The ammonium salt (B) may be any of arbitrary  combinations of cations with anions, both as exemplified  above.  [0087]  The ammonium salt (B) may be synthesized by any  organic chemistry procedures well known to the artisan in  the art. For example, the desired compound may be synthe› sized by mixing a cation-containing compound and an  anion-containing compound in an organic solvent/water  two-layer system, effecting ion exchange reaction therebe› tween, and extracting the organic layer. With respect to the  ion exchange reaction, reference may be made to JP-A  2007-145797, for example. The cation moiety may be pur› chased in the market or synthesized by reaction of a tertiary  amine compound with an alkyl halide, for example. The  anion moiety may be purchased in the market or synthesized  by any well-known procedures. In particular, with respect to  the anion moiety of the compound having formula (5),  reference may be made to JP-A 2007-145797 and JP-A  2009-258695, for example.  [0088]  The resist composition of the invention is success› ful in improving several lithography properties, typically  sensitivity and resolution while maintaining excellent LER.  [0089]  Although the reason is not well understood, it is  presumed that the addition of ammonium salt (B) has a good  influence. Since the ammonium salt (B) has an anion struc› ture which is a conjugated base of strong acid and a cation  moiety which is a quaternary ammonium salt, it is not  decomposed under the action of light or heat in the lithog› raphy process. As used herein, the strong acid refers to a  compound having an acidity sufficient to cleave an acid  labile group in the base resin. On the other hand, the PAG  generates an acid upon exposure. It is believed that part of  the generated acid undergoes salt exchange reaction with the  ammonium salt (B). That is, the acid generated by the PAG  acts on the ammonium salt at a different site, and the counter 