PHOSPHORUS DIFFUSION GETTERING OF GOLD IN SILICON - THE REVERSIBILITYOF THE GETTERING PROCESS

Phosphorus diffusion gettering of gold in silicon is a reversible proc ess with strong temperature and phosphorus concentration dependence. W e show explicitly that gold diffuses back and forth between the highly doped phosphorus layer and the bulk of the material when the annealin g temperature is varied. This was investigated using secondary-ion mas s 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 lon g as the gold concentration is below the solubility limit. The concent ration profile of gold after successful gettering follows the phosphor us profile but virtually all the gold atoms are found in the region wh ere the phosphorus concentration exceeds approximately 3 X 10(19) cm-3 . This is related to a large solubility enhancement of gold when the p hosphorus concentration is above 3 X 10(19) cm-3. The simplest explana tion for the observed gettering mechanism is formation of gold-phospho rus pairs within the highly doped phosphorus layer. However, quantitat ive agreement cannot be obtained between our results and a simple segr egation model based on gold solubilities in lightly doped material and highly phosphorus doped silicon. If the gold solubility in the bulk i s modified by taking into account, proposed supersaturation of silicon self-interstitials agreement between the model and the experimental d ata can be obtained.