Characterization of polycrystalline silicon films grown by LPCVD of silane
Deposition of polycrystalline silicon by thermolysis of silane, SiH4, is a common technique for creating polysilicon films for a variety of applications. The deposition temperature and pressure greatly influence parameters relating to growth rate and film quality. These characteristics include film crystallinity and resulting grain orientation that determine the optical and electrical properties of the films and their suitability for particular applications. An empirical approach was taken to characterize the growth process and resulting film quality. Polycrystalline silicon films were grown to map a region of temperatures and pressures in the range of 575°C to 700°C and 200 mTorr to 500 mTorr. Deposition rate increased with increasing pressure, and was a strong function of temperature, increasing quickly then diminishing due to silane depletion. The crystallinity of films increased with temperature and decreased with pressure, exhibiting regions of rapid transition between amorphous and crystalline phases. X-ray diffraction was used to determine grain orientation and size. The <220> grains showed preferential growth while <111> and <311> grains were completely inhibited at low temperatures. Band gap energy decreased with increasing temperature and crystallinity. Resistivity of as-deposited, intrinsic films was very high. However, planar source phosphorus diffusion and annealing reduced resistivity to as low as 2.5·10−3 [Omega]·m.