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 