Interface recombination velocity measurement by a contactless microwave technique

摘要

The interface or surface recombination velocity (SRV) is a critical and important parameter in many applications. In this work, we have developed and applied a contactless microwave technique, which in combination with a continuously tunable pulsed light source, is able to probe the excess carrier lifetime in the surface and bulk regions of a semiconductor wafer. The technique is called resonant coupled photoconductive decay and has been described by the authors in the literature. For strongly absorbed light, the initial (t = 0) decay time is a strong function of the absorption coefficient a, as well as the bulk lifetime. The effective bulk lifetime is measured by using very weakly absorbed light, or by measuring the asymptotic decay rate of strongly absorbed light. For asymmetric surfaces (such as a wafer polished on one surface only), the measurement with strongly absorbed light is made at both wafer surfaces. We have developed a method to measure SRV independently of bulk lifetime by plotting the surface lifetime data versus the absorption coefficient of the incident light pulse. A number of measurements of silicon wafers, with a variety of surface conditions, will be described.