US Patent 11567406 Positive resist composition and patterning process

A positive resist composition comprising a base polymer comprising recurring units (a) having the structure of an ammonium salt of an iodized or brominated phenol, and recurring units (b1) having an acid labile group-substituted carboxyl group and/or recurring units (b2) having an acid labile group-substituted phenolic hydroxyl group exhibits a high sensitivity, high resolution, low edge roughness and dimensional uniformity, and forms a pattern of good profile after exposure and development.