Selective and Anisotropic Dry Etching of Ge over Si

Abstract

Inductively coupled plasma (ICP) etching of Ge with high selectivity over Si and anisotropic etched profiles using CF₄, HBr, SF₆, and Cl₂ reactive gases has been studied. Because pressure and biased power should be the most important parameters to drive selectivity and etch profile, they were varied from 4 to 50 mTorr and from 0 to 50 W, respectively, so as to investigate their influence on process. Total gas flow (100 sccm) and source power (350 W) were initially held constant. Selectivity greater than 100:1 of Ge over Si was achieved using 100 % Cl₂ etch gas at 50 mTorr and zero bias power but the profile of the etched features was isotropic. With the addition of N₂ to the feed gas (Cl₂) the profile became more anisotropic. A three steps ICP etch process was developed with a final Ge/Si etch selectivity of 5:1 and anisotropic profiles.