Analysis of light elements on Si wafer by vapor-phase decomposition/total reflection X-ray fluorescence

A combination of vapor-phase decomposition (VPD) and total reflection X-ray fluorescence (TXRF), VPD/TXRF, was used for measuring trace elements of Na and Al. A TXRF measurement using W-Mα line was carried out for a highly sensitivity analysis of ultra trace light elements. The technique of VPD/TXRF combining W-Mα excitation could clearly detect the peaks for a sample at a level of 1011 atoms cm-2 that conventional TXRF could not have detected. In the case of 150 mm Si wafers, the lower limits of detection (LLDs) were found to be 3 × 1010 atoms cm-2 and 2 × 109 atoms cm-2 for Na and Al, respectively. The LLDs were improved by two orders of magnitude compared with those of TXRF without using the VPD treatment. The results obtained by VPD/TXRF were cross-checked with the one obtained by AAS. Both values were in good agreement. The glancing-angle dependence of the TXRF intensity was investigated on the samples before and after undergoing the VPD treatment. This dependence proves that the sample after a VPD treatment is the particle type on the wafer.