Determination of the Variation in the Water Content across the Wall of a Fused-Silica Crucible by Transmission Fourier Transform Infrared Spectroscopy

Abstract

One of the uses of fused-silica crucibles is to contain the silicon melt from which semiconductor crystals are grown by the Czochralski method. For three reasons, it is essential that the water content of the crucibles below. First, the softening temperature of the silica is a direct function of the water content. A low water content is necessary to maintain strength and geometry at the high temperatures used in semiconductor crystal growth. Second, water must not cause the contamination of semiconductor crystals. Third, the rate of devitrification is increased by water content. The water content of the crucibles is expected to be uniform, not varying from the inner wall to outer wall. Information on the variation of the water content of fused-silica crucibles is unavailable in the literature. However, transmission infrared spectroscopy has been used to determine water content in fused silica by correlation of the weight loss on heating with the decrease in the absorbance of the Si-OH band at 3680 cm−1. The weight loss is a consequence of the condensation reaction: 2 Si-OH → Si-O-Si + H2O (1)