The Physical and Electrical Properties of Polycrystalline Si 1−x Ge x as a Gate Electrode Material for ULSI CMOS Structures

Poly Si 1−x Ge 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−x Ge x films grown by UHV CVD using Si 2 H 6 and GeH 4 gases, and studied their microstructures as well as their electrical characteristics. The Ge content of the Si 1−x Ge x films increased linearly with the flux of the GeH 4 gas up to x=0.3, and saturated above x=0.45. The deposition rate of the poly Si 1−x Ge x films increased linearly with the flux of the GeH 4 gas up to x=0.1, above which it is slightly changed. The resistivity of the Si 1−x Ge 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−x Ge x gates demonstrated that the flat band voltage of the poly Si 1−x Ge x films was lower than that of poly-Si films by 0.2V.