InP and Phosphorous Allotropes: Safety Lessons from their Processing and Mishandling in Semiconductor Facilities

Barrera, Carlos*; Kemal, Abid
(Exponent, Menlo Park, CA)

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Indium phosphide (InP) is a prevalent compound in the semiconductor industry, particularly in high speed/high bandwidth electronics and solar panel manufacturing. Although InP is a very powerful and efficient semiconductor, its production is complex and relies on the use of dangerous substances, such as phosphine (PH3), or pure solid forms like the so-called red or white phosphorous. Unlike the well-known dangerous properties of the raw materials (e.g. pyrophoric behavior, flammability and toxicity), the deposits formed in the exhaust systems or on the walls of production units are not so well understood. In some cases, these dangers are not considered in the safety assessment of the production process. A thorough understanding of the chemical and physical properties of the various phosphorous allotropes would seem like an obvious requisite for the team charged with the design, operation, or maintenance of a production facility; however, in practice such knowledge is often very limited or simply does not exist. For example, the semiconductor industry has regarded red phosphorous as a stable, safe compound, while white phosphorous is perceived as dangerous and unstable. Much effort has gone into designing systems to remove white phosphorous, but very little attention has been paid to mixed composition deposits where the properties of the various allotropes is unclear and, under certain process conditions, unstable and dangerous mixtures can be formed. Through examples drawn from the investigation and analysis of several incidents involving phosphorous, this paper stresses the importance of considering the formation of reactive species in processing units and their exhaust systems, and how to safely deal with them. This type of information is fundamental when conducting safety assessments, design reviews, and commissioning and maintenance planning.

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