Reactive ion etching of SiGe alloys using CF₂Cl₂

Abstract

The dry etching characteristics of strained Si1-xGex, x≤0.22, thin films (≤1 μm thick) and elemental Si and Ge in CF 2Cl2 reactive ion etching plasmas have been studied by measuring etch rates using in situ ellipsometry, etch profiles using scanning electron microscopy (SEM), and surface-chemical aspects by employing x-ray photoelectron spectroscopy (XPS). The etch rates of the Si1-xGe x alloys increase as a function of Ge content and fall between the etch rates of pure Si and Ge. The etch rate ratios of Si1-xGe x over Si and Ge over Si1-xGex are ∼1.5 and ∼2.4 at a Ge content of 22%, respectively. SEM photographs of the trench profiles in Si1-xGex alloys with either SiO2 or photoresist masks show directional etching characteristics of the CF 2Cl2 reactive ion etching process. The chemically shifted intensities of the Si 2p(1/2, 3/2) and Ge 2p(3/2) core levels indicate a 1- or 2-monolayer-thick reaction layer on the Si1-xGex alloy surface as a result of CF2Cl2 reactive ion etching. Residual Cl is identified as the principle surface impurity by XPS. The first few monolayers of the plasma-exposed SiGe surface is enriched in Si. From a comparison of Si1-xGex etch characteristics with those of Si and Ge etched under identical conditions, we conclude that the behavior of Si1-xGex alloys is very similar to elemental Si.