Minority carrier lifetime results for SOI wafers

SOI technology is based upon the difficult process of fabricating thin silicon films on an insulating layer. This thin silicon layer is the active layer of the device, but it is difficult to obtain electrical characterization of this layer. We are testing a technique for Quality Control and Quality Assessment (QC/QA) by providing rapid, non-invasive, non-contact characterization. This technique is to measure the apparent lifetime of carriers excited by pulsed optical excitation. We infer the effective carrier lifetime from the data by means of an integral of modulating functions with the observed exponentially decaying signal. This provides a robust measure of lifetime with no operator input. This system has been used to determine lifetimes as short as 15 nanoseconds (for a SOI wafer) and as long as 350 μseconds (for a bulk wafer) with a reproducibility of about 10%