The effects of grain boundaries in polycrystalline sheet Si on impurity gettering and O precipitation were investigated by electron beam induced current, deep level transient spectroscopy, micro Fourier-transform infra-red spectroscopy, and preferential etching/Nomarski optical microscopy techniques. Both as-grown and thermally processed wafers were studied. A correlation between grain boundary density and transition metal concentration was quantitatively established by combining deep level transient spectroscopy and electron beam induced current studies. It was found that 4 deep levels arising from Fe–B, Fe–Al, Cr–B, and Fei were present in the as-grown sample, and their concentrations decrease with increasing grain boundary density. Grain boundary gettering was further verified by the presence of an electron beam induced current image contrast halo around the grain boundary. Preferential etching also revealed a precipitate density of 2 x 107/cm2 on the grain boundary. After processing, a clearly defined O precipitate denuded zone formed around the grain boundary with the interstitial O concentration [Oi] decreased from 14.4 to 2.2 x 1017/cm3. Micro Fourier-transform infrared spectroscopy showed that, for both processed and as-grown samples, more Si oxynitride appears in the grain boundary than in the intragrain region. Since N enhanced O precipitation, it was likely that N preferentially precipitated on the grain boundary during the wafer formation process and resulted in a N depletion zone, where O precipitation was further suppressed and a denuded zone formed.

Effects of Grain Boundary on Impurity Gettering and Oxygen Precipitation in Polycrystalline Sheet Silicon. J.Lu, M.Wagener, G.Rozgonyi, J.Rand, R.Jonczyk: Journal of Applied Physics, 2003, 94[1], 140-4