Uniform deposition of in situ doped polysilicon films by ultralow pressure chemical vapour deposition

Abstract

The deposition of uniform doped polycrystalline silicon without the need of complex wafer cages is reported for the first time. Thin films are grown in a specially designed ultralow pressure chemical vapour (ULPCVD) deposition system capable of achieving operating pressures of 0.2mTorr. It is found that at deposition temperatures in the region of 360°C and reactor pressures of less than 5 mTorr uniform doped polysilicon can be deposited. The resistivity and dopant concentrations can be controlled by altering the phosphine-to-silane gas flow ratio. The changes in resistivity with heat treatment are explained in terms of a structural model for grain growth in both LPCVD and ULPCVD thin films.