Physical and mathematical models as well as numerical algorithms for simulation of advanced technological processes, such as thermal annealing after low-energy ion implantation used during the VLSI fabrication are presented. In this paper we propose a model that treats the migration of the impurity atoms at the thermal annealing. We take into account process nonlinearity and influence of non-uniform defects distribution as well as electric field and elastic stress on the migration of atoms. The redistribution of point defects as well as the diffusion of nonequilibrium impurity interstitials in silicon are described by time-dependent quasi-linear parabolic equations. The results of numerical calculations are presented as well.
Ab initio calculations based on the density functional theory have been performed to investigate the migrations of interstitial helium (He) atoms in Au-Ag alloys with two different mass ratios (Au₃Ag₂ and AuAg). The results show that the migration mechanisms of He atoms mainly depend on the crystal structures of alloys, and their migration energy barriers are affected by the migration paths in Au-Ag alloys. He interstitials preferentially occupied the most stable sites, but it is difficult for He interstitials to migrate to nearest most stable sites via second stable positions at room temperature. When He atom is at the tetrahedral position which has higher formation energy, it possibly migrates to nearest tetrahedral positions directly for AuAg alloy. In addition, comparing the migration of He defects in the two alloys, we found that the properties of migration energy and relative stability of He atoms probably slightly depend on the mass-density of Au-Ag alloys.
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