Quantification of outgassing of C-, Si-, and S-containing products during exposure of photoresists

Abstract

Because volatile species containing Si and S desorbed from photoresists during exposure to light can irreversibly damage optical elements inside a photolithography tool, accurate quantification of vapor fluxes is essential to evaluate risk. The authors compare measurements using two vapor-collection methods (gas and ion chromatographies) and one solid state analysis method (secondary ion mass spectrometry) to characterize outgassing from two silicon-containing and two all-organic 193nm photoresists during exposure at atmospheric pressure. Results from all three techniques are in good general agreement with the notable exception of Si-containing products. Investigation of the influence of the gas atmosphere above the resist during exposure reveals that gas-surface interactions involving oxygen and perhaps water are a previously unrecognized mechanism for release of Si during exposure of otherwise inert polymers. This result shows that it is essential to take the gas environment inside the photolithographic tool into account when designing resist polymers for low Si outgassing.