Safe Handling of Compound Semiconductor Exhaust Effluent
Van Gompel, Joe (BOC Edwards, Austin, TX)
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LoginCompound semiconductors such as gallium arsenide, indium phosphide, and indium antimonide use a number of very hazardous gases during deposition steps. These gases include arsine, phosphine, trimethyl indium, germane, silane, dimethyl zinc, and others. Removal of unconsumed process gases, as well as the products of the deposition process, is problematic in that some methods of disposal leave the process engineer with something nearly as toxic as the original gases. Worst among these is arsine, which will always produce an arsenic-tainted waste stream. In addition to the waste gases themselves are the hazards associated with pumping this exhaust, namely the sublimation of pyrophoric elemental phosphorus in the presence of high flows of hydrogen.Treatment of the compound semiconductor process exhaust can best be addressed from a systems approach. Combination of the vacuum line, vacuum pump, exhaust line, and abatement in a single footprint allows for seamless integration into the process. Integration offers significant installation savings as well as CoO advantages. The Zenith 3-5 Integrated Pump / Abatement package integrates the vacuum pump and abatement, allowing for thoroughly heated exhaust lines (eliminates phosphorus buildup) as well as a uniform interface to monitor pump and abatement. The abatement device, typically a Thermal Processor Unit (TPU) or its high H2 variant known as HELIOS, is a combustor / scrubber combination. The TPU provides hydride gas removal to below detectable limits while keeping HCl emissions at or below TLV during the etch step. The combustion products, including arsenic, phosphorus, and gallium oxides, are either filtered as solids in the Water Recirculation Unit or are dissolved in the water and sent to a suitable waste treatment facility capable of removing contaminants to levels acceptable for discharge.