Detection and characterisation of "sleeping" defects in silicon by LBIC scan maps at 80 K.

Annealing of multicrystalline silicon wafers in argon at temperatures higher than 700 degrees C increases the recombination strength of extended defects irreversibly, while external gettering techniques applied at the same temperatures reduce RS. It is observed that in the LBIC scan maps at 80 K the contrast of extended defects in raw samples is enhanced and additional defects are detected. The same features of defects are revealed by the LBIC maps of raw samples at 80 K as well as at 300 K after annealing. In other words the LBIC scan maps at low temperature detect "sleeping" defects, which do not recombine at 300 K, but which are activated by thermal treatments during processing steps. The results can be explained by the Shockley-Read-Hall statistics involving the presence of deep and shallow energy levels in the band gap associated with the impurity defect interaction.