Novel Method for Defect Detection in Al Stripes by Means of Laser Beam Heating and Detection of Changes in Electrical Resistance

We have successfully detected defects (voids and Si nodules) in Al stripes using an optical beam induced current (OBIC) system in which defects, even those beneath a metal surface, were detectable as the difference in changes in resistance, produced by laser beam heating, between defective and defect-free areas. Our method, which we refer to as optical beam induced resistance change (OBIRCH), is nondestructive since the temperature increase caused by laser irradiation is on the order of 1° C and the density of the base current applied to the stripes is on the order of 106 A/cm2 or less. The results of scanning ion microscopy (SIM) (conducted after areas identified by OBIRCH as being defective had been successively cross-sectioned with a focused ion beam [FIB]) indicated that the minimum void size detectable by OBIRCH was on the order of 10-3 µ m3, and we are able to show that OBIRCH has many advantages over conventional void detection methods.