Experimental tests of the steady-state model for oxygen reactive ion etching of silicon-containing polymers

Abstract

A steady-state model based on a silicon material balance has been proposed to predict the oxygen reactive-ion-etching resistance of organosilicon polymers. This model assumes that the rate determining step is sputtering of SiO2 film that forms on the surface of the organosilicon polymer. It predicts the etching rate of organosilicon polymers relative to the sputtering rate of SiO2 , based on the mass density of silicon in the polymer. The steady-state etching rate of a silyl novolac polymer is accurately predicted by the model over a wide range of etching conditions. Silyl methacrylates etch at the predicted rate under high-bombardment-energy conditions typical of trilevel processing, but exceed the predicted rate under low-bombardment-energy conditions. Surface analysis shows that the SiO2 film thickness continues to increase with time under these conditions, invalidating the steady-state approximation. Low silicon content (4.1 wt. %) polymers do not etch according to the model but form highly porous oxides that continuously accumulate on the surface of the polymer.