Safe Removal of Arsenic Dust from Gallium Arsenide Crystal Pullers

摘要

A chemical cleaning process was developed for liquid encapsulated Czochralskicrystal pullers which would reduce the exposure of the operators to arsenic (7440382). In this process the arsenic would be transferred from the puller to a container without releasing arsenic dust into the atmosphere. The arsenic could be converted to arsenic-trichloride which will be carried off in a stream of argon gas into a suitable scrubber. Provided precautions were taken to remove residual moisture from the insulation by vacuum baking and keeping the heater temperature below 500 degrees-C, arsenic could be successfully removed from the puller without any attack on the stainless steel components. Molybdenum-chloride formation was avoided by replacement of molybdenum parts by insert materials such as graphite and alumina. Chloride attack on the crystal occurred even when it was raised to the highest possible position. The authors suggest that the process must be operated by removing crystal and crucible before chlorine transport of the arsenic. While the major exposure to arsenic could be avoided, it appears that some exposure is inevitable during removal of the crystal.