Jul.  30,  2020  4  US 2020/0241418 Al  groups such as phenylene and naphthylene; and tri- or  tetravalent forms of the foregoing groups with one or two  hydrogen atoms being eliminated.  [0050]  The recurring unit (a) functions as a quencher due  to the structure of an ammonium salt of a carboxylic acid  having an iodine or bromine-substituted aromatic ring. 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 recur› ring unit (a) contains iodine atom having high absorption or  bromine atom having a high efficiency of electron emission,  it generates secondary electrons 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.  [0051]  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  acid in recurring unit (a) forms a salt with an alkaline  compound in the developer, leaving the polymer backbone.  This ensures sufficient alkaline dissolution and minimizes  defect formation.  [0052]  Examples of the cation moiety in the monomer  from which recurring units (a) are derived are shown below,  but not limited thereto. Herein  RA  is as defined above.  H~ OWH  )+  RA  -WH  -w› H  L  -continued 