Reduction of Chlorinated Solvents in GaAs Manufacturing
V. Williams, H. Isom, T. Nagle, C. Sellers, S. Hillyard, S. Roadman, S. Varma
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Keywords: chlorinated solvents, wet chemical processing, environmental, replacement chemistries, contact angle, surface roughness, pHEMT, GaAs.
Chlorinated solvents have been used historically in the semiconductor industry for applications such as photoresist removal and surface treatments. However, in recent years, this class of solvents has undergone increased scrutiny, especially from customers in the European Union, leading to a need to find environmentally safer alternatives. Gallium arsenide, in particular, can be subject to surface changes or surface degradation after wet chemical processing, making the selection of replacement chemistries critical. This paper discusses an approach taken successfully to replace chlorinated solvents in some wet clean processes in a GaAs manufacturing facility, specifically focusing on those processes that have been used for pHEMT fabrication. The primary requirement for the success of this project was that the change in wet chemistry would not introduce any parametric changes for existing device technologies. The chosen methodology included surveying a range of chemistries by testing parameters that are predictors of future performance, such as surface contact angles, surface roughness, and material etch rates, followed by selection of solvents and subsequent processing and testing of qualification wafers. Results from all stages of this assessment are presented, including parametric data from fabricated devices and the outcomes of associated DOEs. Potential pitfalls and sources of problems are also discussed.