Modelling of arsenic diffusion in the SiO2/Si system at low-energy implantation and rapid thermal annealing

As the lateral dimensions of modern integrated circuits are scaled down to the nanometer range, the need for accurate models of silicon doping is increased.The manufacturing of modern microelectronics products involves operations leading to a formation of complex systems in near-surface regions of a processed material. The rapid thermal processes are highly transient and are governed by the diffusion and reaction of dopant atoms and defects, and especially by the dynamics of their clusters. Earlier, we have studied various aspects of the modelling of arsenic diffusion in silicon surface regions at rapid thermal annealing. In the present work, we consider model of low-energy implanted As diffusion in the Si/SiO2 interface region of oxidized silicon substrate. The model is taking into account influence of nonequilibrium defects as well as clustering dependence on impurity and electrons concentration. The offered approach allows one to simulate the experimentally observable 'uphill' diffusion. We suggest that arsenic diffusion occurs due to the formation, migration, and dissociation of the As+Dr pairs, where As+ and Dr are the substitutionally dissolved arsenic atom and intrinsic point defect, respectively. At a construction of the model of point defects evolution we assume that As diffusion occurs substantially by the interstitial mechanism, and diffusion by vacancies is less significant. Therefore we consider only the equation describing diffusion of point defects induced by transfer of intrinsic interstitial atoms. A thermodynamic approach based on the local equilibrium between the substitutionally dissolved arsenic, point defects and the pairs leads to the system of two diffusion equations: the equation of dopant atoms diffusion and the equation of diffusion of point defects. In the present work we used special approach to the consideration of the impurity transport through Si/SiO2 boundary which allows to get rid of artificial parameters such as 'boundary transport rate' and consider the impurity concentration to be continuous. Consequently, the proposed model allows simulation of high concentration transient enhanced diffusion of As implanted in Si, although this transport process differs substantially from the diffusion processes described by the Fick's second law. (authors)