Fast metal diffusers in Si in the presence of Si self-interstitial traps

Abstract

The diffusion of Au, Pt, and Zn in Si yield Si self-interstitial diffusivities, DI, that exceed those obtained from dopant marker experiments by 6 orders of magnitude at 800 °C. Both types of experiments can be reconciled by assuming the existence of a nonannihilating interstitial trap, related to carbon. In this context, selected metal diffusion data are reanalyzed. Nonannihilating immobile traps and a second-order reaction involving interstitial carbon and carbon–carbon pairs are considered. Quantitative point-defect parameters are extracted at 1115 °C for an assumed trap concentration of Ctt=5×1016 cm−3. In all cases and independent of the value of Ctt, excellent fits to concentration versus depth profiles of Zn are obtained; the extracted equilibrium concentration of Si self-interstitials, CI*, varies inversely with Ctt, while DICI* remains approximately constant. Hence agreement, or disagreement, of metal diffusion results with the Si self-diffusion coefficient cannot be used to exclude or prove trap-limited diffusion. Literature values of point-defect parameters obtained by neglecting traps represent lower bounds on DI and upper bounds on CI*. The time evolution of the Zn profile in the presence of traps is discussed. Proper inclusion of traps in the analysis of metal diffusion data leads to a decrease in the extracted activation energy of DI.