Feb.4,2021  22  US 2021/0033971 Al  [0062]  Non-Patent Document 1 points out that the decom› position of an acid generator, typically triphenylsulfonium  salt is provoked not only by light exposure, but also with  radicals. This suggests that the resist material is improved in  sensitivity if many radicals generate upon light exposure.  [0063]  An iodized or brominated hydrocarbyl group (ex› clusive of aromatic ring in which iodine or bromine substi› tutes on a carbon atom) generates radicals upon EUV  exposure. The aromatic ring having iodine or bromine  bonded thereto is stable enough to generate no radicals upon  EUV exposure, whereas iodine or bromine bonded to a  carbon atom other than a carbon atom on aromatic ring is  detached upon EUV exposure, to generate radicals. The  radicals promote decomposition of an acid generator to  bring an increase of sensitivity.  [0064]  The recurring unit (a) functions as a quencher due  to the structure of an ammonium salt of an iodized or  brominated carboxylic acid. In this sense, the base polymer  may be referred to as a quencher-bound polymer. The  quencher-bound polymer has the advantages of a remarkable  acid diffusion-suppressing effect and improved resolution.  In addition, since the recurring unit (a) contains iodine atom  having great photo-absorption or bromine atom having a  high electron generation efficiency, it generates secondary  electrons or radicals to promote decomposition of the acid  generator during exposure, leading to a high sensitivity. As  a result, a high sensitivity, high resolution, and low LWR or  improved CDU are achieved at the same time.  [0065]  Iodine or bromine is less soluble in alkaline devel› oper because of a relatively large atomic weight. When  iodine or bromine is attached to the polymer backbone, a  resist film in the exposed region is reduced in alkaline  solubility, leading to losses of resolution and sensitivity and  causing defect formation. When the recurring unit (a) is in  an alkaline developer, the iodized or brominated carboxylic  -continued  Br  Br  ~o  ~o  0  9-<:  0  <o  ---<o  Br  Br  ~o  0  9-<  -;:o 