Properties of Polycrystalline Si[sub 1−x]Ge[sub x] Films Grown by Ultrahigh Vacuum CVD Using Si[sub 2]H[sub 6] and GeH[sub 4]

Abstract

Polycrystalline Si1-xGexfilms 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-Si1-xGexfilms by using ultrahigh vacuum chemical vapor deposition CVD with Si2H6and GeH4gases, and studied their physical properties as well as electrical characteristics. The deposition rate and Ge content of poly-Si1-xGexfilms increased linearly with the flux of GeH4up to a critical GeH4flux, while, above this critical flux, it is slightly changed. The resistivity of poly-Si1-xGexfilms 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 WSix/poly-Si1-xGexgates demonstrated that the flatband voltage of the poly-Si0.55Ge0.45films 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 WSix/poly Si0.55Ge0.45gate structure were investigated. Leakage current levels increased slightly due to the difference in VFBwith the increase of Ge content in poly Si1-xGexfilms.