Phosphorus diffusion gettering of gold in silicon: The reversibility of the gettering process

Abstract

Phosphorus diffusion gettering of gold in silicon is a reversible process with strong temperature and phosphorus concentration dependence. We show explicitly that gold diffuses back and forth between the highly doped phosphorus layer and the bulk of the material when the annealing temperature is varied. This was investigated using secondary-ion mass spectroscopy to study the gold within the gettering layer and using deep level transient spectroscopy to estimate the gold content in the bulk. We observed no internal gettering or outdiffusion of gold as long as the gold concentration is below the solubility limit. The concentration profile of gold after successful gettering follows the phosphorus profile but virtually all the gold atoms are found in the region where the phosphorus concentration exceeds ∼3×1019 cm−3. This is related to a large solubility enhancement of gold when the phosphorus concentration is above 3×1019 cm−3. The simplest explanation for the observed gettering mechanism is formation of gold-phosphorus pairs within the highly doped phosphorus layer. However, quantitative agreement cannot be obtained between our results and a simple segregation model based on gold solubilities in lightly doped material and highly phosphorus doped silicon. If the gold solubility in the bulk is modified by taking into account, proposed supersaturation of silicon self-interstitials agreement between the model and the experimental data can be obtained.