Studies of plasma surface interactions during short time plasma etching of 193 and 248 nm photoresist materials

As the device dimensions scale to 100 nm, the use of photoresist materials is suitable for lithographic patterning at 193 nm. The molecular structure of 193 nm photoresist materials is significantly different from that of 248 nm photoresist materials H. Ito, IBM J. Res. Deu. 45, 683 2001, T. Kajita et al., Proc. SPIE 4345, 712 2001, which leads to a number of undesirable consequences, including pronounced surface and line edge roughness during plasma etching H. Ito, IBM J. Res. Deu. 41, 69 1997, E. Reichmanis et al., J. Vac. Sci. Technol. B 15, 2528 1997, L. Ling et al., ibid. 22, 2594 2004. In this article, we present an investigation of the mechanisms for the surface/line edge roughening of photoresist materials during plasma etching using C4F8 /90% Ar discharges. We emphasized in our study short exposure times the first few seconds of the photoresist materials and structures to the plasma, a time regime that has not been well studied. Rapid modifications were observed for both 193 and 248 nm photoresists during short time exposure. During the first seconds of plasma exposure, photoresist material densification and hydrogen depletion are important processes. It is also found that rough surfaces develop within a few seconds of exposure to the C4F8 /90% Ar discharges. Plasma exposure leads to the formation of rough edges on the top of trench sidewalls in photoresist trench and line structures. During prolonged exposure to the plasma, the roughness is transferred to produce striations on the sidewalls. After an initial stage, the roughening rate remains constant for 193 nm photoresist, whereas for 248 nm photoresist the roughening rate is negligible. This difference is possibly related to the preferential removal of carbonyl groups for the 193 nm photoresist material, which has been revealed by x-ray photoelectron spectroscopy and seconday ion mass spectroscopy.