Polysilicon Etchback Plasma Process Using HBr , Cl2, and SF 6 Gas Mixtures for Deep‐Trench Isolation

Abstract

Etchback of polysilicon used for refilling deep trenches isolating bipolar devices has been investigated in a magnetically enhanced reactive ion etcher using , , and gas combinations. Etch rates, uniformities, and loading effects have been studied as a function of gas mixtures. Polysilicon etchback processes with uniformity better than 2%, polysilicon etch rate larger than 5000 Aå/min, and loading factor less than 1.3 were obtained with a gas mixture consisting of less than 9 sccm flow in a predominant and mixture. It was found that the etch roughness and surface profile of the resulting trench polysilicon was a strong function of percentage in the mixture. The controllable trench polysilicon etchback profile with smooth surface and curvature was obtained by using 60 sccm and 50 sccm gas mixtures with 6 sccm gas flow.