Nondestructive magneto-optical characterization of natural and artificial defects on 3" HTSC wafers at liquid nitrogen temperature

Double-sided 3" HTSC wafers were characterized by the magneto-optic technique. The presented apparatus allows a nondestructive and fast detection of local and extended inhomogeneities in the critical current density with high lateral resolution in the micrometer range. Additional gold-layers on the HTSC wafers, as they are sometimes used for the device production, do not influence the characterization result. The high sensitivity of the presented apparatus allows even the detection of local defects at higher temperature (77 K) where contrasts in the critical current are weaker and the magneto-optical characterization of HTSC thin films is much more difficult than at lower temperatures. So the apparatus can be used even under conditions where cooling with liquid helium or closed-cycle refrigerators is not available. The sensitivity was tested on natural and artificial defects, the latter being prepared by means of a focused laser beam.