Perfect-Selectivity Directional Etching of Silicon Using Ultraclean ECR Plasma

An ultraclean electron cyclotron resonance (ECR) plasma etcher was newly devetoped and Si wafers nasked by SiOq were etched with a chlorine plasna at pressures of 0.6-4.0 nTorr with a nic-rowave power of 300-?00 W. As a result of ultraclean processlng, it was found that at hish pressures the SiOe etch delays although Si ls etched without deIay. During the delay pe-rfect selective etching for Si to Si0r is achieved. Under the hishly selective condition, anisotropic lower sub-micron patterns of polysilicon have been obtained with little undercut. A method to detect the just-etched polnt was developed using wafer voltage neasurements.