Interface Recombination Velocity Measurement by a Contactless Microwave Technique

The interface or surface recombination velocity is a critical and important parameter in many device 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 life-time in the surface and bulk regions of a semiconductor wafer. The technique is called resonant coupled photoconductivc decay (RCPCD) 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, α, as well as the bulk lifetime. The effective bulk lifetime is a well-known function of the two surfaces (interfaces) and the true 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. The latter occurs after diffusion has produced a quasi-equilibrium condition in the wafer. 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 solved simultaneuously three nonlinear equations, and the solutions provide values for the three unknowns S₁, S₂ and τ(bulk). Several examples of the technique will be demonstrated for silicon wafers.