Using minority carrier lifetime measurement to determine saw damage characteristics on Si wafer surfaces

The damage on the Si wafer surfaces, caused by ingot cutting, is determined from measurement of minority carrier lifetime (τeff). Samples are sequentially etched to remove thin layers from each surface and lifetime is measured after each etch step. The thickness-removed at which the lifetime reaches a peak value corresponds to the damage depth. This technique also allows the depth distribution of the damage to be quantified in terms of surface recombination velocity (SRV). An accurate measurement of τeff requires corrections to optical reflection, and transmission to account for changes in the surface morphology and in the wafer thickness.