Atomistic Simulations of Epitaxial Regrowth of As-doped Silicon
- PDF / 824,691 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 105 Downloads / 231 Views
1070-E03-09
Atomistic Simulations of Epitaxial Regrowth of As-doped Silicon Joo Chul Yoon, and Scott Dunham Electrical Engineering, University of Washington, Seattle, WA, 98195 ABSTRACT We conducted molecular dynamics (MD) simulations of solid phase epitaxial growth of As-doped Si using a Tersoff potential characterized via comparison to density functional theory (DFT) calculations, including energies of AsnV clusters. The Si:As systems were initialized by amorphizing the surface region of crystalline silicon via Si ion implantation. The remaining crystalline region provides dual function of controlling temperature in system without perturbing regrowth and providing seed for recrystallization. After recrystallization, isolated As atoms occupy substitutional sites, with the average number of nearest neighbors for As changing from about 3.3 in amorphous Si to 4 after crystallization. We observe V incorporation associated with high As concentrations, primarily at sites with multiple As neighbors. These observations are consistent with our previous model developed to explain kinetics of As shallow junction formation which assumed V incorporation at sites with 2 or more As nearest neighbors to account for experimental data. INTRODUCTION Amorphization has become a ubiquitous part of doping technology as it enables sharper doping profiles (via reduction of channeling and TED) and high metastable dopant activation. The state of the material following regrowth determines to a large extent the final profile broadening and activation level even when SIMS shows no apparent change in the dopant distribution. This is because purely local rearrangements can lead to clustering and point defect incorporation. A key example of this is diffusion of high concentration As implants. Our work has indicated that formation of As-vacancy complexes during regrowth has a major impact on diffusion and activation in ultra-shallow junctions even when followed by a high temperature RTA [1]. The impact of processes in the amorphous material becomes even more critical as thermal budgets are reduced. A promising approach for ultra-shallow junctions is to limit annealing (RTA and flash) to just enough to allow recrystallization. For such processes, redistribution and activation in amorphous material and near amorphous/crystalline interface fully controls final structure. In contrast to crystalline regions, for which there are a small number of equivalent sites, for amorphous (or just heavily disordered) regions, every microscopic region is different. Thus, one cannot use a small number of ab-initio (DFT) calculations to identify rate limiting processes and parameters and then apply the resulting model at each site. Also, because it is necessary to look at relatively large regions of the material in order to predict properties, ab-initio techniques cannot practically consider sufficiently large systems to capture the behavior of amorphous materials and amorphous/crystalline interfaces. Thus, we apply classical molecular dynamics methods in this work.
ARS
Data Loading...
