Detection of the extent of the laser damaged gettering effect using nondestructive surface acoustic wave technique

Nondestructive evaluation of the minority carrier lifetime is performed using the Surface Acoustic Wave (SAW) technique. Samples under study are commercially used silicon wafers with the Laser Induced Damage (LID) covering half of the back of each wafer. Minority carrier lifetime which is a measure of the defect concentration on the device side is measured at the damaged (gettered) and undamaged regions of each wafer using SAW technique. The comparison of the results shows about 2 fold increase in the lifetime in the gettered area. The bulk generation lifetime measured by Capacitance-Time (C-T) technique does not show this increase. The reason is attributed to the decrease in the surface generation velocity above the damaged area. The SAW measurement does not require any MOS fabrication and can be performed nondestructively after each thermal cycle.