Silicon oxidation during bilayer resist etching

Abstract

Steady-state etching rates and initial film losses were measured for two types of silicon-containing polymers (polysiloxanes and polysilylstyrenes) under a variety of oxygen plasma conditions. While steady state behavior was observed for most conditions, the silylstyrene resists showed higher etch rates than predicted from recent models. The deviations were explained by the fact that the oxidized layer formed from silylstyrene polymers has a large residual carbon content, and thus sputters at a rate higher than predicted for a stoichiometric Si02 layer. The siloxane material showed good agreement with the model under all conditions and was determined to form a more Si02-like oxidized layer. XPS analysis was used to monitor the conversion of carbon-bound silicon to oxidized species for the polysilylstyrenes. Conversion was more rapid and more complete when etching with higher ion energies. Polysilylmethylstyrene reached a steady-state oxide thickness between 3.4 and 5.8 nm, depending on etching conditions. A copolymer of this material with chloromethylstyrene showed a comparable thickness when etched at high ion energies, but did not reach a steady state when etched at conditions where the average ion energy was below 110 eV. © 1989 SPIE.