Evaluation of outgassing from a fluorinated resist for 157nm lithography

Abstract

We have evaluated the outgassing products and the in situ transmittance of a contaminated CaF2 substrate for monocyclic fluoropolymers with four protecting groups: methoxymethyl (MOM), tert-butoxycarbonyl (t-BOC), menthoxymethyl, and 2-cyclohexylcyclohexyloxymethyl. We found little correlation between the total amount of outgassing from the polymer and the decreasing rate of the CaF2 substrate transmittance caused by outgassing adhesion. Although the MOM protecting group generated the largest amount of outgassing products, the most substantial decrease in the transmittance was observed for the t-BOC protecting group. Therefore, the absorption coefficient of the outgassing-contaminated CaF2 substrate appears to be more sensitive to the type of protecting group, especially the t-BOC protecting group including a t-butyl unit. We conclude that in terms of material design of the fluoropolymer resist for 157nm lithography, we need to pay attention to the protecting group of polymers, especially the protecting group including a t-butyl unit, which generates isobutene product during 157nm irradiation.