Properties of polycrystalline Si_1-xGe_x films grown by ultrahigh vacuum CVD using Si₂H₆ and GeH₄

Polycrystalline Si_1-xGe_x films have been suggested as a promising alternative to the currently employed polycrystalline silicon (poly-Si) gate electrode for complementary metal oxide semiconductor field effect transistor technology due to lower resistivity, less boron penetration, and less gate depletion effect than that of poly-Si gates. We investigated the formation of poly-Si_1-xGe_x films by using ultrahigh vacuum chemical vapor deposition CVD with Si₂H₆ and GeH₄ gases, and studied their physical properties as well as electrical characteristics. The deposition rate and Ge content of poly-Si_1-xGe_x films increased linearly with the flux of GeH₄ up to a critical GeH₄ flux, while, above this critical flux, it is slightly changed. The resistivity of poly-Si_1-xGe_x films decreased as the Ge content increased, and was about one-half of that of poly-Si films at a Ge content of 45%. The capacitance-voltage measurements of metal oxide semiconductor capacitor structures with WSi_x/poly-Si_1-xGe_x gates demonstrated that the flatband voltage of the poly-Si_0.55Ge_0.45 films was lower than that of poly Si films by 0.2 V. In addition, the changes of flatband voltage with the dosage of boron and the sudden decrease of accumulation capacitance in the WSi_x/poly Si_0.55Ge_0.45 gate structure were investigated. Leakage current levels increased slightly due to the difference in V_FB with the increase of Ge content in poly Si_1-xGe_x films.