Arsenic deactivation enhanced diffusion: A time, temperature, and concentration study

Abstract

The electrical deactivation of arsenic in silicon has been studied with regard to its effect on enhanced diffusion. Experimental structures consist of a buried boron layer as an interstitial detector, and a fully activated arsenic doped laser annealed surface layer. As these structures are annealed at temperatures between 500 and 750 °C, arsenic in the surface layer deactivates and we observe enhanced diffusion of the buried boron layer. A study with time reveals that the enhanced diffusion transient and the deactivation transient are similar, indicating a strong correlation between both phenomena. The dependence on concentration shows a maximum enhanced diffusion for concentrations between 3 and 4×1020 cm−3 of initially active arsenic. Above these concentrations, the large supersaturation of interstitials nucleates dislocation loops and lowers the overall enhancement measured in the buried boron layer. Temperature data show that even for temperatures as low as 500 °C, enhanced diffusion is observed. These data are convincing evidence that the enhanced diffusion observed is due to the deactivation of arsenic and provides important insights into the mechanisms of deactivation. We propose that arsenic deactivation forms small clusters of various sizes around a vacancy with the injection of an associated interstitial into the bulk.