DEPENDENCE OF LIFETIME ON SURFACE CONCENTRATION OF COPPER AND IRON IN SILICON-WAFERS

Minority-carrier lifetime after oxidation is investigated with a laser-microwave photoconductance (LM-PC) method for silicon wafers deliberately contaminated with Cu or Fe of different surface concentrations. The secondary ion mass spectroscopy (SIMS) depth profile clearly correlate the effect of those impurities on the bulk and surface components, which are obtained with a recently developed algorithm, of the effective lifetime. Copper impurities diffused from the wafer surface segregate at the SiO2/Si interface and near-interface region, and the surface component becomes dominant at high-surface contaminations. On the other hand, most of the iron segregates in the oxide layer and the residual iron diffuses into the bulk region, and therefore the bulk component dominates the effective lifetime.