The chemical reaction near the crucible wall during directional solidification of Si crystals for solar cells has been investigated. Fragments of the crucible that were used for the crystal growth of a Si ingot were examined. As results, we found that a chemical reaction took place at the coating/crucible interface and that silicon oxynitride particles precipitated near the crucible wall. The oxynitride precipitates were determined as stoichiometric Si2N2O and were revealed not to be amorphous but of orthorhombic crystal symmetry. We show crucial evidence of the formation of stoichiometric Si2N2O microcrystalline precipitates inside the Si crystal.

Multicrystalline silicon grown by the cast method and used in photovoltaic cells includes nitrogen from the Si3N4 coating of the SiO2 crucible. We investigated the distribution of nitrogen, existing as NN or NNO complexes in silicon, by Fourier transform infrared spectroscopy. We found that the NN peak intensity was higher at the upper part of the silicon ingot, while the NNO peak intensity was higher at the lower part. There was a complementary relationship between the distribution of NN and that of NNO; this implied that NNO complexes were formed by NN complexes that had combined with interstitial oxygen during crystal growth.

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