Evidence of impurity gettering by industrial phosphorus diffusion

The possible benefits of phosphorus gettering as applied to production multicrystalline silicon wafers have been evaluated. After optimization of an open tube POCl3 process, relatively low temperatures and short times have been found to significantly improve the minority carrier lifetime of most wafers. The possible gettering action stemming from the industrial process of phosphorus diffusion has also been investigated and found to be similarly effective. Average lifetimes of 45 mus (diffusion length of 360 mum) were obtained, with some wafers reaching maximum values up to 130 mus. Lifetime monitoring of a commercial cell fabrication line has also enabled characterization of the voltage limits imposed by the standard emitter and aluminum back-surface-field. The results indicate that the bulk, as improved by emitter gettering, is generally not the limiting factor on cell performance.