Provided herein are, inter alia, bioreactive unnatural amino acids, compounds containing the unnatural amino acids, and methods of using same.

An onium salt monomer consists of an anion having an aromatic ring substituted with a polymerizable group and iodine, a substituent containing a fluorosulfonic acid anion structure and a substituent containing an iodized aromatic ring being appended to the aromatic ring, and a cation. A resist composition comprising a polymer comprising repeat units derived from the monomer exhibits a high solvent solubility, high sensitivity and high contrast and forms a small-size pattern having satisfactory lithography properties such as LWR and CDU as well as etch resistance.

An onium salt monomer consists of an anion having an aromatic ring substituted with a polymerizable group and iodine, a substituent containing a fluorosulfonic acid anion structure and a substituent containing an iodized aromatic ring being appended to the aromatic ring, and a cation. A resist composition comprising a polymer comprising repeat units derived from the monomer exhibits a high solvent solubility, high sensitivity and high contrast and forms a small-size pattern having satisfactory lithography properties such as LWR and CDU as well as etch resistance.