Nonequilibrium simulation method for the study of directed thermal processing

Abstract

A nonequilibrium molecular-dynamics computer-simulation method is developed for the study of directed thermal processing, in particular laser annealing. A strong heat gradient is applied to a substrate using entities called ‘‘energy carriers,’’ which supply a given energy fluence over a given pulse duration with a known intensity-time shape (Gaussian, here). The thermodynamic, kinetic, and structural properties of the substrate are calculated during the ensuing melting and resolidification. Properties such as the melt depth, interface temperature, and interface velocity are calculated as a function of time, allowing predictions of the extent of superheating and supercooling to be made. From these results, the interface response function (interface velocity versus temperature) can be constructed. This function shows an asymmetry of melting and freezing kinetics (the former being significantly faster), in accord with recent experimental results. The sensitivity of the method to the modeling of the energy carriers, the system size, and pulse duration is discussed. Results are presented for a system of Lennard-Jones atoms, with an exposed (100) fcc face, and shown to be in good qualitative agreement with experimental results for silicon.