Directional etching of Si with perfect selectivity to SiO2 using an ultraclean electron cyclotron resonance plasma

Abstract

Using a newly developed ultraclean electron cyclotron resonance plasma etcher, Si wafers masked by SiO2 were etched with a chlorine plasma at pressures of 0.6–4.0 mTorr with a microwave power of 300–700 W. Ultraclean processing under a low ion energy condition at high pressures has revealed that there is an induction period during which time there is no SiO2 etching. This is not observed with Si. During the induction period, perfectly selective etching for Si to SiO2 has been achieved. Under this perfectly selective condition, anisotropic tenth micron patterns of polycrystalline silicon have been obtained with little undercut.