Evolution of cristobalite clusters on silica glass surfaces in molten silicon

Crystal growth at the interface between silica glass and molten silicon was investigated to clarify the formation process of a ring structure at the surface of Czochralski crucibles. A cluster of faceted cristobalite at the interface was found to grow laterally and then transform into a ring with disappearance of the faceted crystals at the central region. The production of the cristobalite cluster is explained by dissolution of silica glass into molten silicon and deposition of crystalline cristobalite at a nucleation site. Redissolution of the crystal at the central area of the cluster resulted in the formation of a ring structure. It is deduced that the nucleation site of cristobalite clusters is provided by the devitrification of silica glass.