Papers by Keyword: Non-Equilibrium Point Defects

Abstract: Ion implantation of different dopants (donors and acceptors) into crystalline silicon with subsequent thermal annealing is used for the formation of ultra-shallow p-n junctions in VLSI technology. The experimentally observed phenomenon of transient enhanced diffusion (TED) during annealing hinders further downscaling of advanced VLSI circuits. However, modern mathematical models of dopant diffusion, which are based on the so-called “five-stream” approach, and software packages such as SUPREM4 encounter difficulties in describing TED. In this work, an extended five-stream model for diffusion in silicon is developed, which takes into account all the possible charge states of point defects (vacancies and silicon self-interstitials) and diffusing pairs “dopant atom–vacancy” and “dopant atom–silicon self-interstitial”. The model includes diffusion and drift of differently charged point defects and pairs in the internal electric field and the kinetics of interaction between unlike species. The expressions for diffusion fluxes and sink/source terms that appear in the non-linear, non-steady-state reaction-diffusion equations are derived for both donor and acceptor dopants accounting for multiple charge states of the diffusing species.

Abstract: It is known experimentally that solid-state interdiffusion is substantially enhanced during plastic deformation. This is especially noticeable in Mechanical Alloying (MA) which is used for producing a wide range of metastable materials (supersaturated solid solutions, amorphous phases, nanostructures) with unique properties. However, a physical mechanism of enhanced diffusion during MA is not clearly understood yet, and a comprehensive model of this complex phenomenon has not been developed so far. Moreover, the role of the diffusion process in MA is hotly debated in literature. In this work a new, self-consistent mathematical model of solid-state interdiffusion in a binary substitutional system A-B during periodic plastic deformation is developed. The model includes basic physical factors that affect diffusion, such as generation of non-equilibrium point defects by gliding screw dislocations during deformation and their relaxation in periods between impacts. The cross-link terms are considered, and interaction of point defects with edge dislocations and incoherent phase boundary A/B is taken into account. Computer simulation is performed using realistic data (e.g., quasi-equilibrium self-diffusion coefficients known in literature) and the process parameters typical of MA in a vibratory mill. A repeated “deformation-rest” cycle is considered. The results of modeling reveal the physical mechanism of the enhancement of solid-state diffusion by periodic plastic deformation during MA and demonstrate that within the frame of this approach supersaturated solid solutions can form within a reasonably short processing time.