Conduction Properties of Chemically Deposited Polycrystalline Silicon

The relation between the conduction properties of the polycrystalline silicon films and process parameters such as the dose of implanted impurities, the deposition temperature, and heat-treatment were investigated. The doping concentration in polycrystalline silicon film was precisely controlled by ion implantation techniques. The trapping state density at the grain boundary which was the most important factor for the conduction properties of polycrystalline silicon was calculated using the doping concentration and experimentally obtained potential barrier height. It was found that the trapping state densities were 3.5 x 10¹²/cm² for the boron-implanted polycrystalline silicon deposited at 700°C, and 5.2 x 10¹²/cm² for the phosphorus-implanted polycrystalline silicon, respectively. The trapping state density was found to be reduced by increasing the deposition temperature or by the heat-treatment of the film at high temperature after the deposition of the polycrystalline silicon. It was also revealed that even a very small amount of oxygen caused the increase of the trapping state density.