Modeling of effect of interfacial charges on impurity diffusions in silicon-on-sapphire device processing

The existence of interfacial states and fixed charges between the silicon and sapphire films create an electric field that affects the diffusion of impurities near the interface. The effect of this field is modeled as a new term in the diffusion equation. A computer program was written to numerically integrate the diffusion equation for a one-dimensional model. The results were correlated with SIMS data for high-concentration phosphorus profiles. A predicted peak in the phosphorus concentration at the silicon-sapphire interface, due to the effect of negative charges at that interface, was confirmed. A pipe diffusion model was incorporated to account for the higher (than bulk silicon) diffusivities observed. New values of skewness were also needed to match implanted profiles with Pearson-IV type distributions.