Influence of vignetting on signal analysis of photocarrier radiometry of semiconductor wafers

Abstract

The influence of vignetting on the photocarrier radiometry (PCR) measurements of semiconductor wafers has been investigated both theoretically and experimentally by analyzing the vignetting effect on the PCR amplitude and on the frequency dependence of the PCR amplitude and phase. The vignetting effect significantly reduces the PCR amplitude and modifies the frequency dependencies that are widely used to extract simultaneously the electronic transport properties (that is, the carrier lifetime, the carrier diffusion coefficient, and the front and rear surface recombination velocities) of semiconductor wafers. When using the frequency dependence of the PCR signal to determine the transport properties, the effect of vignetting can be accounted for by an “effective detector size”—a reduced detector size determined by the actual detector size and the vignetting effect.