Low-Pressure Chemical Vapor Deposition of Semi-Insulating Polycrystalline Silicon (SIPOS) and its Analysis: Application to Power Diode Passivation

摘要

This paper deals with semi-insulating polycrystalline films (SIPOS), deposited by the Low Pressure Chemical Vapor Deposition (LPCVD) technique by pyrolysis of nitrous oxide (N_2O) and silane (SiH_4), in order to passivate the surface of silicon power diodes to improve its breakdown characteristics. The physical and electrical features of these films are studied in function of the following deposition parameters: temperature, total pressure, N_2O/SiH_4 gas flow ratio. The composition of the film is obtained from Rutherford Back Scattering and X-Ray Diffraction analyses. The deposition temperature and total pressure do not significantly modify the crystallinity of the film. An increase of the N_2O/SiH_4 ratio increases the total oxygen atom incorporation and thus increases the resistivity of the film. An increase of the temperature increases also the oxygen incorporation. In these conditions, the tunnelling conduction model through the thin oxide is experimentally confirmed; the conductivity is exponentially dependent of the oxygen content in the film. Applied to power diode passivation, SIPOS film deposited at 700°C with a N_2O/SiH_4 ratio of 0.3 allows to reach an improvement of 25% in the breakdown voltage, when compared with polymer passivated diodes.