Abstract
We report here the unintentional doping of silicon device wafers during furnace operations caused by a volatile organophosphate contaminant in the clean room ambient. The unintentional doping is characterized electrically using spreading resistance and sheet resistance measurements. The onset of the unintentional doping was found to coincide with the installation of new high efficiency particulate air (HEPA) filters. Using static secondary ion mass spectroscopy and gas chromatography techniques on monitor wafers exposed to the clean room ambient, the contaminant was identified as phosphorus in the form of Fyrol PCF, an organophosphate flame retardant. Fyrol was traced to the polyurethane potting material used in the HEPA filters to secure and seal the filter media in place. The unintentional doping was caused by exposure of the furnace dummy wafers to the clean room ambient air during the period between oxidations. These wafers then acted as phosphorus dopant sources during device wafer oxidation.