VPD/TXRF analysis of trace elements on a silicon wafer

A combination of vapor-phase decomposition (VPD) and total reflection x-ray fluorescence (TXRF) was used for the trace analysis of light elements (Na and Al) and transition metals (Fe, Ni, Cu, and Zn). TXRF measurement using the W Mα line was conducted for the high-sensitivity analysis of Na and Al. Through the use of VPD/TXRF, the lower limits of detection (LLDs) were improved by two orders of magnitude compared with those of TXRF without use of the VPD technique. For 150 mm Si wafers, the LLD was 3 × 1010 atoms cm−2 for Na and 2 × 109 atoms cm−2 for Al. The LLDs for Fe, Ni, Cu, and Zn were 4 × 107, 5 × 107, 6 × 107 and 9 × 107 atoms cm−2, respectively. The analytical results obtained by VPD/TXRF were cross-checked with results obtained by atomic absorption spectrometry. The two sets of values were in good agreement. The glancing angle dependence of TXRF intensity was investigated on samples before and after undergoing VPD treatment. The angle dependence proved that the sample after VPD treatment became a particle type on the wafer. Copyright © 1999 John Wiley & Sons, Ltd.