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

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.