The detection limit for synchrotron radiation total reflection x-ray fluorescence (SRTXRF) that can routinely be achieved for transition metals is about 8E7 atoms/cm² for a standard 1000 second counting time. Theoretically, the SRTXRF detection limit of 8E7 atoms / cm² could be further reduced to 3.6E4 atoms/cm² by using a pre-concentration process such as vapour phase decomposition (VPD). In VPD process, the contaminants on the wafer surface will be collected into a single droplet and the droplet will be dried on the wafer surface for TXRF analysis. During the process, however, impurities in the UPW (ultra pure water), chemicals, wafer surface, or from handling cannot be ignored. Our investigation of wafers subjected to diff e rent cleaning processes has revealed that background signals on the dry spot could arise from the VPD process itself. Therefore, the baseline that is determined by the purity of the UPW, starting chemicals and wafers limits the detection limits of VPD-SRTXRF. Read more