Selective and Anisotropic Dry Etching of Ge over Si

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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.