LOW-TEMPERATURE (LESS-THAN-OR-EQUAL-TO-600-DEGREES-C) SEMIINSULATING OXYGEN-DOPED SILICON FILMS BY THE PECVD TECHNIQUE FOR LARGE-AREA POWERAPPLICATIONS

This work describes the deposition, annealing and characterisation of semi-insulating oxygen-doped silicon films at temperatures compatible with polysilicon circuitry on glass. The semi-insulating layers are de posited by the plasma enhanced chemical vapour deposition technique fr om silane (SiH4), nitrous oxide (N2O) and helium (He) gas mixtures at a temperature of 350 degrees C. The as-deposited films are then furnac e annealed at 600 degrees C which is the maximum process temperature. Raman analysis shows the as-deposited and annealed films to be complet ely amorphous. The most important deposition variable is the N2O/SiH4 gas ratio. By varying the N2O/SiH4 ratio the conductivity of the annea led films can be accurately controlled, for the first time, down to a minimum of approximate to 10(-7) Omega(-1) cm(-1) where they exhibit a T--1/4 temperature dependence indicative of a hopping conduction mech anism, Helium dilution of the reactant gases is shown to improve both film uniformity and reproducibility. A model for the microstructure of these semi-insulating amorphous oxygen-doped silicon films is propose d to explain the observed physical and electrical properties.