Effect of Doping and Oxidation on Grain Growth in Polysilicon

ABSTRACTWe have studied the influence of doping and oxidation on grain growth of small grain polysilicon. Intrinsic and phosphorus doped (to 1021 /cc pseudo-amorphous layers of Si were prepared by chemical vapor decomposition of SiH4 at 600°C on thermally grown SiO2 on Si wafers. These samples were then annealed in N2 or O2 ambients at 1000°C for 30 minutes. Transmission electron microscopy examination of the samples revealed that grain boundary dislocations were commonly present at high angle boundaries and that there was a remarkable disparity in mean grain size, d, for the different samples. It was found that d was greater for (a) doped poly than intrinsic poly annealed in either N2 or O2, and (b) for the same polysilicon starting materials (doped or undoped) annealed in O2 than in N2. We propose that these phenomena may be explained by the influences of dopant and point defects on grain boundary dislocation mobility which in turn governs grain boundary migration. An atomistic model of grain boundary migration has been developed. A key aspect of the model is the formation and motion of jogs and kinks on grain boundary dislocations. These processes are directly influenced by the behavior of point defects in the material and its electronic properties.