Metal contamination monitoring and gettering

Some commonly used techniques for metal contamination monitoring by lifetime measurements (surface photovoltage, Elymat and microwave-detected photoconductive decay) are discussed and compared. In order to validate these techniques for the detection and the quantitative evaluation of bulk-diffused contamination, iron and chromium implanted samples have been studied. Though these techniques are very different from each other, we show that for what concerns bulk-diffused impurities they agree very well with each other, provided in the comparison the dependence of carrier lifetime on the injection level is taken into account. In addition, the possibility to extend these techniques to surface characterization (e.g. for the detection of surface-precipitated metals) is studied. Nickel and copper implantated wafers were used to this purpose. Both Elymat and μ-PCD are found to be very sensitive to surface-segregated metals, though under these conditions the correlation between Elymat and μ-PCD data is somewhat different with respect to samples with metals dissolved in the bulk. Finally, some gettering techniques are reviewed and compared for what concerns gettering efficiency. It is pointed out that gettering efficiency is sensitively reduced in high temperature rapid thermal treatments. This fact can be explained by efficiency loss of the segregation mechanism.