Effect of Grain-Boundaries on the Solubility of Copper in Silicon

Solubility studies of copper in high-purity vapour-grown polycrystalline silicon have given direct evidence for strong solute-atom/grain-boundary interactions in this system. The interaction energy between copper-atoms and grain-boundaries was ascribed to chemical bonding and was determined to be -1.47 +/- 0.04 eV. Since the grain-structure of the vapour-grown material was found to be very complex, a precise determination of the actual grain-boundary solubility was not possible. A theoretical calculation based on enthalpic considerations (neglecting changes in thermal entropy) estimated the ratio of the grain-boundary solubility to the single-crystal solubility to be similar or equal to 4 X 10(5) at 700 degrees C.