Spatially resolved lifetimes in EFG and string ribbon silicon after gettering and hydrogenation steps

Lifetime improvement in EFG and string ribbon silicon by gettering or defect passivation has been investigated by photoconductance decay. But in contrast to former studies measurements have been carried out in a spatially resolved way. In this way the mapping techniques have been found to be indespensable for an accurate study of processing steps´ impact on material quality. This is due to very strong lifetime variations that have been measured throughout the wafer (between <1μs and >300μs), and because areas of the same starting quality have turned out to react very differently on applied processing steps. Consequently the results of integral measurements strongly depend on the nature of the areas incorporated in the specific sample. A statistical evaluation of the mapped lifetimes gives an impression of the uncertainties inherent to integral measurements.