Comparison of Silicon Photoluminescence and Photoconductive Decay for Material Quality Characterization

Abstract

AbstractMinority-carrier lifetime in silicon directly relates to defect- and impurity-related recombination, and thus gives a measure of material quality. Lifetime measurements are useful in research laboratories and commercial production environments as an indicator for process development and quality control. While photoconductivity (PCD) techniques for measuring lifetime are commercially available, there has recently been interest in using photoluminescence (PL) to characterize lifetime in silicon because of the measurement speed to image an entire wafer and higher mapping resolution. The intensity of band-to-band PL is theoretically proportional to the effective bulk lifetime in low-injection conditions if carrier diffusion and re-absorption are neglected, surface recombination is small, and silicon properties, such as carrier concentration and the radiative recombination coefficient, are constant. We show data that compare lifetimes from PCD techniques to PL intensity for varying-resistivity, single-crystal silicon. Surface conditions are also varied (native oxide, thermal oxide, and HF etch/methyl-iodine solution), and the measured lifetimes are compared to corresponding PL intensity.