Effect of grain boundary on electrical characteristics in B- and P-doped polycrystalline Si1−x −yGexCy film deposited by ultraclean LPCVD

The effect of grain boundary on electrical characteristics in B- and P-doped polycrystalline (poly) Si1−x −yGexCy films was investigated. Poly-Si1−x −yGexCy films were deposited on thermally oxidized Si(100) at 500-650 °C in a SiH4-GeH4-SiH3CH3-H2 gas mixture by an ultraclean hot-wall low-pressure chemical vapor deposition. B and P were doped into the films by ion implantation and diffusion by heat-treatment. The electrical properties are characterized by grain size, width of disordered region near grain boundaries, carrier trap density and the amount of impurity segregation at grain boundaries. In the B-doped poly-Si1−x −yGexCy films heat-treated at 900 °C, the increase of carrier concentration npoly and the decrease of resistivity ρpoly with Ge addition are caused by the narrowing of the width of disordered regions, i.e., crystallization of disordered regions induced by Ge atoms. The decrease of npoly and the increase of ρpoly with C addition are explained by the suppression of crystallization of disordered region due to C atom segregation at grain boundaries. In the P-doped poly-Si1−x −yGexCy films, it is found that npoly and ρpoly are influenced by P atom segregation at grain boundaries due to lowering solid solubility of P in grain by the existence of Ge.