Precipitate recognition and recombination strength in annealed Czochralski silicon wafers

Abstract

Two experimental methods have been used to reveal the presence of precipitates and to evaluate their recombination strength in Czochralski grown silicon wafers. One method uses scanning infrared microscopy, the other light beam induced current mapping. These two non-destructive techniques have been associated with Fourier transform infrared spectroscopy and with minority carrier diffusion length measurements. After two step annealing, scanning infrared microscopy reveals the presence of precipitates, while light beam induced current mapping displays a ringlike distribution of recombination centres and the minority carrier diffusion length decreases drastically to 2 μm. Copper contamination does not modify these observations even when precipitates are formed. Phosphorus diffusion near the surface decreases the size of the precipitates revealed by scanning infrared microscopy but does not suppress the ringlike light beam induced current maps, and the minority carrier diffusion length increases slightly. It is concluded that the recombination strength of precipitates does not depend on metal decoration but more probably on interfacial states or on associated extended defects.