Provided are sulfonyldiazomethane compounds and photoacid generators suited for resist materials which generate less foreign matters after application, development and peeling, and in particular, are excellent in the pattern profile after the development; and resist materials and patterning process using them. Provided are sulfonyldiazomethane compounds represented by formula (1): ##STR00001## Also provides are photoacid generators containing the sulfonyldiazomethane compounds, and a chemical amplification resist material comprising (A) a resin which changes its solubility in an alkali developer by action of an acid, and (B) a sulfonyldiazomethane compound of formula (1) capable of generating an acid by exposure to radiation. Provided is a patterning process comprising steps of applying the above-described resist material onto a substrate to form a coating, heating the coating, exposing the coating, and developing the exposed coating in a developer after an optional heat treatment.