REACTIONS BETWEEN LIQUID SILICON AND VITREOUS SILICA

Oxygen incorporation in silicon crystals during Czochralski growth is dependent on many factors, of which the dissolution of the silica crucible is of great importance. In this paper the reactions between vitreous silica and molten silicon have been analyzed, both in sealed ampoules and in Czochralski crucibles. It was found that the vitreous silica crystallizes to cristobalite by lateral growth. For this reaction to occur it is necessary that liquid silicon is present. The vitreous silica dissolves and the cristobalite grows with a thin layer of liquid silicon between them. Different oxygen concentrations in the melt in equilibrium with the amorphous and crystallized silica are necessary for the reaction to proceed. The oxygen flux in the melt is dependent upon the dissolution of both vitreous silica and cristobalite as well as the reaction between these phases.