Non-contact evaluation of semiconductors using a laser SQUID microscope

The distribution of a photo-induced magnetic field from a p-n junction is measured by a laser SQUID microscope that consists of a high temperature superconductor SQUID magnetometer and a laser diode. The maximum magnetic field of several pico-tesla is detected at the depletion layer of the p-n junction. At the point where the laser spot and p-n junction have symmetry, the magnetic field reaches the minimum. The minority carrier diffusion length is also obtained by using two wavelengths of excitation light. The,photon flux density ratio is measured in each wavelength so that the photo-induced magnetic field can be equal. The minority carrier diffusion length is related to the photon flux density ratio. The results are in good agreement with the value obtained by spreading resistance profiling method. Since the laser SQUID microscope can evaluate the minority carrier diffusion length without any contact, this method is useful for contamination free in-process monitoring of the p-n junction. (C) 2002 Elsevier Science B.V. All rights reserved.