COMPARISON AMONG LIFETIME TECHNIQUES FOR THE DETECTION OF TRANSITION-METAL CONTAMINATION

A systematic comparison among the most common methods (surface photovo ltage (SPV), Elymat, and microwave-detected photoconductive decay (mu- PCD)) for lifetime measurements is presented. Though these techniques are very different from each other, we show that, where bulk-diffused impurities are concerned, they agree very well with each other, provid ed they are properly used. In order to validate these techniques for t he quantitative evaluation of bulk-diffused contaminants, iron and chr omium implantations were carried out. An excellent correspondence was found between Elymat and mu-PCD data. In addition, the lifetime depend ence on iron dose was studied and the expected behaviour was verified over two orders of magnitude. Elymat and mu-PCD measurements have also been applied to the study of contaminants segregated at wafer surface , such as nickel and copper. Both these techniques are very sensitive to surface-segregated metals, though under these conditions the correl ation between Elymat and mu-PCD data is somewhat different with respec t to samples with metals dissolved in the bulk. A measurement procedur e is proposed in order to discriminate bulk and surface recombination.