Surface contaminations on silicon wafers — Monitoring of cleaning processes and specifying wafer quality

We describe here an analytical technique suitable for fast and reliable determination of surface metal content on solar wafers, serving as powerful tool for monitoring cleaning processes and specifying wafer quality. A method called surface-extraction-ICPMS (SE-ICP-MS) was developed, adapted from the pack-extraction method suggested by Shimazu and Ishiwari [3]. Basically, the complete wafers are immersed in an extraction solution consisting of acids with variable concentrations. The concentration of dissolved trace elements is than determined quantitatively by high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). By using this SE-ICPMS method we analysed the trace elements separately on the outer surface, in the oxide layer and in the Si bulk (including the region containing saw damages). In addition, laser ablation-ICP-MS and ToF-SIMS analysis were performed on the same surfaces and showed a good correlation to the SE-ICPMS results.