MINORITY-CARRIER LIFETIME MEASUREMENT IN EPITAXIAL SILICON LAYERS

The minority carrier lifetime is measured in the silicon epitaxial lay er. The lifetime is 8.0 ms in an as-received n/n epitaxial layer. This time is due to the carrier recombination at the Si surface. A lifetim e of 120 ms is obtained after passivation of the epitaxial layer surfa ce. Since this lifetime is affected largely by the carrier recombinati on al the substrate, lifetime of the epitaxial layer cannot be measure d directly even by measurement as a wavelength of 520 nm. Therefore. t he lifetime can be determined only by subtracting the lifetime of the substrate water from the observed value. This measurement and calculat ion give a minority carrier lifetime of an n-epitaxial layer as 450 mu s. This lifetime is much greater than that of the substrate. However, it deviates widely within a wafer, for instance, from 102 to 450 mu s . However, the origin of the lifetime deviation is not clear. This lif etime measurement technique makes it possible to deposit a high qualit y and uniform epitaxial layer by improving the deposition conditions.