Sidewall protection by nitrogen and oxygen in poly-Si1−xGex anisotropic etching using Cl2/N2/O2 plasma

Sidewall protection by nitrogen and oxygen in poly-Si1−xGex anisotropic etching has been investigated using electron-cyclotron resonance (ECR) chlorine plasma. It was found that the sidewall protection with only N2 addition is weaker than that of poly-Si. Highly anisotropic etching of poly-Si0.5Ge0.5 is achieved by the addition of both N2 and O2. In the investigation of X-ray photoelectron spectroscopy (XPS) for poly-Si0.5Ge0.5 after the radical dominant etching, it was found that the sidewall protective layer is scarcely formed on Ge surface by not only N2 addition but also by O2 addition. From these results, it is suggested that highly anisotropic etching of poly Si0.5Ge0.5 is achieved by the etching protection of both N and O on the sidewall against chlorine radical etching.