Hexavalent Chromium Production/Decay during Mask Production Process

Ratliff, John
(Applied Materials, Hillsboro, Oregon)

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Last year we found that the chromium which was released from the plasma etch process when making mask patterns is a form of hexavalent chromium. We did wipe sampling of the inside of the chamber initially, and found low levels of total chromium inside the chamber. The author conducted a literature search, and uncovered several papers which detailed the chemical reactions which released hexavalent chromium from this process. Then earlier this year, we removed one of our etchers, and sampled the ducts behind it. We sampled initially for total chrome, then went back and got hexavalent chrome wipe samples. We found a significant percentage of the total chromium was hexavalent chromium. This is important because ducts contaminated with hexavalent chromium must be decontaminated. SEMI S14 gives a formula for calculating the level of surface chemical contamination (in this case hexavalent chromium). This allows variables to be used to calculate the “Surface Contamination Assessment Criteria (HBCLoral). This calculation uses the reference dose from the EPA, mass fraction transferred skin to mouth, gastro-intestinal absorption factor and a few others (for which we use assumed values, such as body weight), to determine the level of surface contamination allowed. My paper would go over both the generation of the hexavalent chromium and the HBCLoral determination, and discuss the implications of this for decontamination of ducts during decommissioning of equipment.

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