The influence of oxygen precipitates in the bottom part of multicrystalline silicon ingots on the metal diffusion was studied. According to the well known haze test, an experimental setup for the measurement of diffusion velocity at 700C was developed, in which the copper was detected using total reflection X-ray fluorescence. Differences in the diffusion velocity and the gettering amount for copper in samples with low-oxygen and high-oxygen were observed. Thus gettering efficiency seemed to be dependent on oxygen content. Metal precipitates detected were found to contain Si, O and Cu. Since these precipitates appeared along grain boundaries, it was assumed that grain boundaries acted as a diffusion channel. As a consequence, oxygen precipitates located at the grain boundary should be most effective for intrinsic gettering. The results of these studies were encouraging since they implied that an optimized oxygen precipitate concentration in the bottom zone of a multicrystalline silicon ingot could be used as an effective intrinsic diffusion barrier.

The Influence of Oxygen Precipitates on the Diffusion Velocity of Copper in the Bottom Parts of mc-Si Ingots. J.Walter, A.Krause: Energy Procedia, 2012, 27, 59-65