Outgassing of organic vapors from 193 nm photoresists: Impact on atmospheric purity near the lens optics

Fourteen different 193 nm photoresists were tested for organic vapor outgassing after exposure and their outgassing rates were measured to be between 1011 and 1013 molecules cm−2 s−1, with the primary compounds being isobutene and benzylic photoacid generator fragments. Rough estimates indicate that for an outgassing rate of 1011 molecules cm−2 s−1 and a well purged tool, organic vapor partial pressures between 10 ppb and 1 ppm are likely, depending on the lens working distance. Higher levels of outgassing combined with poor ventilation can result in partial pressures in excess of 1 Torr. These values exceed the residual ambient levels expected in a fab and hence constitute an increased risk of contamination to the final optical element of 193 nm exposure tools.