Structural and electrical properties of polycrystalline silicon films deposited by low pressure chemical vapor deposition with and without plasma enhancement

Silicon thin films prepared by chemical vapor deposition of silane at very low pressures (4 mTorr) in an experimental reactor that allows deposition with and without plasma enhancement have been characterized. The temperature range of the substrates on which the films were deposited was varied from 500 to 800° C for plasma-enhanced depositions and 600 to 800° C for nonplasma depositions. Conductivity measurements as a function of temperature as well as average grain size and crystallographic texture measurements were performed. The results indicate that the films deposited with the assistance of a plasma were amorphous at deposition temperatures of 650° C and below and polycrystalline at deposition temperatures of 700° C and above. In the temperature regime investigated, this amorphous-to-crystalline transition was not observed in films deposited without the assistance of a plasma. Furthermore, all the films deposited at temperatures of 650° C and below have been found to have significantly different properties from the similarly prepared films deposited at higher temperatures.