Selective chemical etching of polycrystalline SiGe alloys with respect to Si and SiO2

Polycrystalline SiGe etches that are selective to silicon dioxide as well as silicon are needed for flexibility in device fabrication. A solution of NH₄OH, H₂O₂, and H₂O has been found to selectivity etch polycrystalline silicon-germanium alloys over both silicon and silicon dioxide. Optimum composition of the solution was determined by maximizing etch rates for SiGe films with several germanium compositions. The dependence of etch rates on germanium content, etching temperature, and doping concentration are reported. The etch rate and selectivity are approximately exponentially proportional to the germanium content. Etching was found to be insensitive to deposition method, doping method, and annealing conditions of the SiGe films. In addition, etching leaves a smooth silicon substrate surface after removal of SiGe films.