Measurement of carrier lifetime profiles in diffused layers of semiconductors

This paper describes a method for the measurement of carrier generation lifetime profiles within diffused layers in semiconductors. Knowledge of the lifetime distribution is the key to being able to accurately predict terminal electrical properties as well as understanding the physical processes operating in devices. In addition, the lifetime profile should be a sensitive measure of the quality of the device processing. Although many methods have been developed and applied to the measurement of lifetime in uniformly doped semiconductor regions, this is the first time that lifetime profile measurements have been achieved within diffused layers. In this paper, the lifetime measurements were done by the ZERBST technique using an MOS capacitor created by anodization of the wafer surface. The use of ZERBST plots allows the easy separation of surface recombination from the bulk lifetime eliminating one major source of error during lifetime measurements. In addition, the MOS capacitor used for the lifetime measurement can also be used for the measurement of the carrier concentration allowing excellent correlation between the lifetime and the doping concentration. The anodization techniques used for these measurements allow the stripping of small sections of even shallow diffused layers providing good depth resolution during the profiling. Using this method of lifetime profiling, lifetime measurements have been made up to concentrations of 10¹⁸atoms/cm³in both n- and p-type diffused layers in silicon.