Quantitative analysis of surface contaminants on silicon wafers by means of TOF-SIMS

Measurement of surface metal contamination on silicon wafers is essential for yield enhancement in IC manufacturing. Vapour phase decomposition coupled with either inductively coupled plasma mass spectrometry (VPD–ICP-MS), or total reflection X-ray fluorescence (VPD– TXRF), TXRF and, more recently, TOF-SIMS are used to monitor surface metal contamination. These techniques complement each other in their respective strengths and weaknesses. For reliable and accurate quantification, so-called relative sensitivity factors (RSF) are required for TOFSIMS analysis. For quantification purposes in VPD, the collection efficiency (CE) is important to ensure complete collection of contamination. A standard procedure has been developed that combines the determination of these RSFs as well as the collection efficiency using all the analytical techniques mentioned above. Therefore, sample wafers were intentionally contaminated and analysed (by TOF-SIMS) directly after preparation. After VPD–ICP-MS, several scanned surfaces were analysed again by TOF-SIMS. Comparing the intensities of the specific metals before and after the VPD-DC procedure on the scanned surface allows the determination of so-called removing efficiency (RE). In general, very good agreement was obtained comparing the analytical techniques after updating the RSFs for TOF-SIMS. Progress has been achieved concerning the CE evaluation as well as determining the RSFs for 16 elements more precisely for TOF-SIMS.