Effects of fluid inclusions in quartz sand on fused silica crucible

Abstract

High-purity quartz sands are used to manufacture the fused silica crucibles. However, their influences on gas bubble evolution and cristobalite formation in fused silica crucibles in the Czochralski silicon (Cz-Si) growth process remain unclear. In this work, we propose a method to precisely define and quantitively analyze the fluid inclusion contents of quartz sands through the processing of optical microscope images of quartz sands. Based on it, the gas bubble evolution of two different fused silica crucibles made from two batches of quartz sands are investigated after vacuum annealing treatment for simulating the Cz process. Quantitively analysis shows that higher fluid inclusion contents lead to higher initial gas bubble density, which can further influence the gas bubble evolution during vacuum annealing. In addition, the corresponding analysis on cristobalite formation behavior shows that the fused silica crucibles made of quartz sand with higher alkali metal concentrations are proved to be more prone to the formation of cristobalite during vacuum annealing, although the total concentration is only ∼16 ppm. These results can contribute to the purification and selection of high-purity quartz sands, in particular, special attention should be paid to the further removal of Li, Na and K elements, which helps to improve the high-temperature stability and lifetime of fused silica crucibles.