Diffusive molecular dynamics simulations of boron diffusion in Si-B δ-layers

Atomic Precision Advanced Manufacturing (APAM) technology has been identified as one of the candidates to fabricate novel, beyond-Moore devices at the limit scaling. APAM enables the creation of 2D doped regions, or δ-layers, in semiconductors with atomic precision. One of the main challenges of this manufacturing process is preventing B atoms from diffusing out of the δ-layer into the Si substrate or cap of the semiconductor, which would degrade the electrical properties of the δ-layer. On one hand, elevated temperatures are required to grow a pristine Si cap with minimal defects, but on the other hand, excessively high temperatures must be avoided to suppress B diffusion. Achieving an optimal balance therefore requires a careful trade-off between these competing factors. Diffusive molecular dynamics (DMD) is a framework that can be utilized to help simulate the APAM process. Unlike traditional molecular dynamics, DMD can handle long timescales, useful in simulations of molecular diffusion and mass transport. Using DMD simulations in the program LAMMPS, we investigate diffusion of B atoms from the δ-layer into crystalline c-silicon in APAM systems at different annealing temperatures. Results found that at temperatures less than 700K, total diffusion of B did not occur, but above this threshold, diffusion occurred rapidly and the δ-layer disappeared. Within this temperature range, partial B diffusion occurs, leading to an increase in the δ-layer thickness.