Germanium etching in high density plasmas for 0.18 μm complementary metal–oxide–semiconductor gate patterning applications

Oxide masked polysilicon/polygermanium 0.18 μm gates were etched in high density plasma sources. Using gas mixtures of Cl2 and HBr with O2 which are commonly used for polysilicon, we observed strong deformation of the poly-Si/poly-Ge gate profiles, whereas perfectly anisotropic etching profiles were obtained for poly-Si gates. A multistep etching recipe was developed allowing anisotropic etching profiles to be obtained while maintaining a good selectivity to the gate oxide when using a Cl2/N2 gas mixture. The chemical constituents present on the tops, sidewalls, and bottoms of the etched features were determined by x-ray photoelectron spectroscopy (XPS). XPS analyses have shown that when using a Cl2/N2 gas mixture, a thin GeNx passivation layer is formed on the sidewalls of the poly-Ge features.