High resolution lifetime scan maps of silicon wafers

High resolution lifetime mappings of excess minority carriers in silicon wa fers are obtained by means of the phase-shift technique at practically cons tant injection level. This technique is contactless, based on reflected mic rowave power variations which occur when the sample is illuminated by a foc used near infrared light. It measures the phase shift phi between a sinusoi dal modulation of the excitation and the reflection power of microwaves. Su rfaces are passivated by means of an aqueous iodine solution, whose passiva ting efficiency is remarkably constant. Scan maps are obtained with a later al resolution of 50 mu m by means of a coaxial cable which directs 9.4-GHz microwaves onto the wafer and a fiber coupled laser diode which generates m inority carriers in excess. Lifetime mappings are in agreement with minorit y carrier diffusion length mappings obtained by the light beam induced curr ent technique, especially for multicrystalline wafers. (C) 2000 Elsevier Sc ience S.A. All rights reserved.