Quantitative evaluation of bulk-diffused metal contamination by lifetime techniques

In this paper we present a systematic comparison among the most common methods (surface photovoltage, Elymat and microwave-detected photoconductive decay) for lifetime measurements. The possibility to identify contaminants and to quantitatively evaluate their concentration by lifetime techniques is investigated. Though these techniques are very different from each other, we show that in relation to bulk-diffused impurities, they agree very well with each other, provided that the dependence of carrier lifetime on the injection level is taken into account when comparing them. Iron and cromium implanted wafers are used in order to validate these techniques for the quantitative evaluation of bulk-diffused contaminants. Iron concentrations obtained from lifetime data are compared to measurements of chemical concentration of iron at wafer surface. A very good correlation is obtained between estimates of iron concentration from lifetime data and O2-leak SIMS data in samples contaminated by implantation of dopant ions.