Grain boundary diffusion of aluminum in polycrystalline silicon films

Grain boundary diffusion of Al in poly-Si films has been measured by an Auger sputter profiling technique in a temperature range of 350-425°C. The Al atoms were observed to diffuse through Si grain boundaries, then accumulated near a poly-Si/SiO2 interface. By concentrating on the initial stage of diffusion, the diffusion problem was analyzed using a simple model in which a steady-state flux of Al though Si grain boundaries is accumulated by an effectively infinite sink at the poly-Si/SiO2 interface. Auger measurements yielded quantitative information regarding the concentration gradient in the middle of the poly-Si layer and the amount of accumulation near the poly-Si/SiO2 interface. From this information, the grain boundary diffusion coefficient of Al in Si Db was determined. The temperature dependence of Db fits an Arrhenius-type relation with D °b =1.3×107 cm2/s and Qb =2.64 eV. The measured activation energy was found to be consistent with that of the grain boundary diffusion of P and B as well as the dislocation diffusion As in Si.