Photo-acid generator having aromatic ketone structure for ArF chemically amplified resist

We designed dialkylsulfonium salts with an aromatic ketone structure (a 1-indanone, 1-tetralone, or 4-chromanone unit) as a photo-acid generator (PAG) for ArF chemically amplified resists. Their thermal stability was affected by the alkyl subsitituents; sulfonium salts with two methyl groups or a pentamethylene group exhibited a decomposition temperature of more than 200 °C. The absorption coefficients at 193 nm for the new PAGs were 1/3 to 1/4 that of the conventional triphenylsulfonium salt. The photo-acid generating efficiencies of these sulfonium salts for an ArF laser were influenced by the ketone structures. The efficiency of the sulfonium salt with the 1-tetralone group was higher than the others. A positive resist using a dimethyl(1-oxo-2-indanyl)sulfonium salt achieved a 0.13 μm L/S pattern.