Fourteen different 193 nm photoresists were tested for organic vapor outgassing after exposure and their outgassing rates were measured to be between 10(11) and 10(13) 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 10(11) 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.