Fabrication of high quality strained SiGe on Si substrate by RPCVD

In this study, the growth kinetics of SiGe in a reduced pressure chemical vapor deposition system using dichlorosilane (SiH₂Cl₂) and germane (GeH₄) as the Si and Ge precursors were investigated. The SiGe growth rate and Ge content were found to depend on the deposition temperature, GeH₄ flow and reactor chamber pressure. The SiGe growth rate escalates with increasing deposition temperature, while the Ge content is reduced. The SiGe growth rate accelerates with increasing GeH₄ flow, while the Ge content increases more slowly. According to the experimental data, a new relationship between Ge content (x) and F(GeH₄)/F(SiH₂Cl₂) mass flow ratio is deduced: x ^2.5/(1−x) = nF(GeH₄)/F(SiH₂Cl₂). The SiGe growth rate and Ge content improve with increasing reactor chamber pressure. By selecting proper precursor flows and reactor pressure, SiGe films with the same Ge content can be fabricated at various temperatures. However, the quality of the SiGe crystals is clearly dependent on the deposition temperature. At lower deposition temperature, higher crystalline quality is achieved. Because the growth rate dramatically drops with lower temperatures, the optimum growth temperature must be a compromise between the crystalline quality and the growth rate. X-ray diffraction, Raman scattering spectroscopy and atomic force microscopy results indicate that 650°C is the optimum temperature for fabrication of Si_0.75Ge_0.25 film.