Effect of grain microstructure on P diffusion in polycrystalline-on-single crystal silicon systems

Abstract

Grain microstructure has a major impact on diffusion of P in polysilicon-on-single crystal silicon systems both within the polysilicon layer and inside the single crystal silicon substrate. During annealing, P diffuses very rapidly along grain boundaries in the polysilicon layer to the interface, where it undergoes very fast diffusion laterally along the polysilicon-single crystal silicon interface, followed subsequently by slow indiffusion into the underlying substrate. However, the extrapolated Secondary Ion Mass Spectrometry profiles for P reveal a discontinuity at the interface, which is caused by anomalous diffusion behavior similar to the well known “kink” effect observed in single crystal silicon during P diffusion. The high diffusivity tail region is also much less pronounced for polysilicon-on-silicon systems compared to single crystal silicon due to a reduction of interstitial supersaturation in the substrate. This reduction is believed to result from the absorption of interstitials by the grain boundaries which act as sinks for the excess interstitials.