Work function of impurity-doped polycrystalline Si1−x−yGexCy film deposited by ultraclean low-pressure CVD

Work function of in situ heavily P- or B-doped poly-Si1−x−yGexCy films were investigated. The poly-Si1−x−yGexCy films were deposited on thermally oxidized Si(1 0 0) at 550 °C using an ultraclean hot-wall low-pressure chemical vapor deposition system in a SiH4–GeH4–SiH3CH3–dopnat (PH3 or B2H6) gas mixture, and the gate-to-substrate work function difference was estimated from flat-band voltage determined by high-frequency capacitance–voltage measurement. With increasing Ge and C fractions, the work function of B-doped poly-Si1−x−yGexCy film decreases, although that of P-doped poly-Si1−x−yGexCy scarcely changes. X-ray diffraction results show that the lattice constant increases with the C fraction, in other words, C is incorporated at interstitial site in the film at least at 550 °C. It is suggested that the change in the work function of doped poly-Si1−x−yGexCy is universally explained by the change in the lattice constant as function of the Ge and C fractions.