Low-temperature crystallization of in situ phosphorus-doped low-pressure chemical-vapour deposited amorphous silicon

Abstract

A method has been developed for producing low-resistivity phosphorus-doped polysilicon films with a minimum thermal budget. The method involves low-pressure chemical-vapor deposition of amorphous silicon at 560 °C followed by crystallization at 650 °C. Films formed in this manner are compared to films deposited polycrystalline at 627 °C. In both cases, in situ doping is achieved by addition of PH3 diluted in SiH4 to the gas mixture. For a given SiH4: PH3 flow ratio, the phosphorus concentration determined from secondary-ion mass spectroscopy is four times larger in the amorphous-deposited material. Moreover, the resistivity is substantially lower in this material even when the dopant concentrations are similar. The latter result may be due in part to reduced dopant segregation to grain boundaries. The internal strain determined from the Raman line width is larger in the polycrystalline-deposited material but could be reduced by high-temperature annealing.