The physical and electrical properties of polycrystalline Si_1-xGe_x as a gate electrode material for ULSI CMOS structures

Poly Si_1-xGe_x films have been suggested as a promising alternative to the currently employed poly-Si gate electrode for CMOS technology due to lower resistivity, less boron penetration, and less gate depletion effect than those of poly Si gates. We investigated the formation of poly Si_1-xGe_x films grown by UHV CVD using Si₂H₆ and GeH₄ gases, and studied their microstructures as well as their electrical characteristics. The Ge content of the Si_1-xGe_x films increased linearly with the flux of the GeH₄ gas up to x=0.3, and saturated above x=0.45. The deposition rate of the poly Si_1-xGe_x films increased linearly with the flux of the GeH₄ gas up to x=0.1, above which it is slightly changed. The resistivity of the Si_1-xGe_x films decreased as the Ge content increased, and was about one half of that of poly-Si films at the Ge content of 45%. The C-V measurements of the MOSCAP structures with poly Si_1-xGe_x gates demonstrated that the flat band voltage of the poly Si_1-xGe_x films was lower than that of poly-Si films by 0.2V.