Influence of extended defects and native impurities on external gettering in polycrystalline silicon

The ability of phosphorus diffusion to remove metallic impurities from polycrystalline silicon is analysed in this paper. The intragranular and grain boundary electrical activity into the gettered substrate is investigated using the light-beam-induced current technique. It is pointed out that the bulk minority carrier diffusion length is strongly degraded even during external gettering treatment (15–120 min, 850 and 950 °C): the phorphorus layer does not act as an effective sink for impurities. Our results show also that the grain boundary barriers increase with increasing temperature and annealing duration of these treatments. From these observations, we conclude that the native impurities are activated during subsequent annealing depending on the thermal history of the crystal and that the limiting factor for the gettering efficiency would be the interaction between native point defects and extended defects. In addition, arguments are provided to explain the temperature dependence on external gettering observed in this work.