Lifetime Characterization of Poly-Silicon Back Sealed Wafers with Bi-Surface Photoconductivity Decay Method

Abstract

ABSTRACTBi-surface photoconductivity decay (BSPCD) method has been useful to obtain the true bulk lifetime and surface recombination velocities in silicon wafers with variously finished surfaces. Thermally oxidized n-type CZ silicon wafers with and without a poly-Si back seal (PBS) were characterized with the BSPCD method using 500 MHz-UHF wave reflection. It has been found that the surface recombination velocity of the PBS surface is, 4027 cm/s while that of the no-PBS surface is 16 cm/s, for example. The very fast surface recombination velocity is attributed to the poly-Si / Si interface character. Moreover, the bulk lifetime calculated in the PBS wafer is much higher than that in the no-PBS one, which reveals the PBS gettering performance for the thermal oxidation induced contamination.