A model has been developed for the rapid melting and resolidification of thin Si films induced by excimer-laser annealing. The key feature of this model is its ability to simulate lateral growth and random nucleation. The first component of the model is a set of rules for phase change. The second component is a set of functions for computing the latent heat and the displacement of the solid–liquid interface resulting from the phase change. The third component is an algorithm that allows for random nucleation based on classical nucleation theory. Consequently, the model enables the prediction of lateral growth length (LGL), as well as the calculation of other critical responses of the quenched film such as solid–liquid interface velocity and undercooling. Thin amorphous Si films with thickness of 30, 50, and 100 nm were annealed under various laser fluences to completely melt the films. The resulting LGL were measured using a scanning electron microscope. Using physical parameters that were consistent with previous studies, the simulated LGL values agree well with the experimental results over a wide range of irradiation conditions. Sensitivity analysis was done to demonstrate the behavior of the model with respect to a select number of model parameters. Our simulations suggest that, for a given fluence, controlling the film’s quenching rate is essential for increasing LGL. To this end, the model is an invaluable tool for evaluating and choosing irradiation strategies for increasing lateral growth in laser-crystallized silicon films.
We have developed excimer-laser-annealing (ELA) modeling capability by broadening the computational ability of a standard finite-element based computational-fluid-dynamics software package to adopt to the specific demands of very rapid heating of thin a-Si films. This was achieved by the incorporation of a subroutine employing a phase function and a set of rules for determining latent heat absorption or release. With this enhancement the model was able to correctly calculate the degree of superheating/undercooling in the film and track the melt-solid interface velocity. The model also provided reasonable estimates of the expected poly-Si lateral growth length as a function of the laser irradiation scenario. The model in its current form is a useful tool for first order calculations and for supporting relevant experimental studies.
In this paper we present our work on the numerical simulation of ultrarapid heating (with phase-change) of silicon thin-films, which are irradiated with nanosecond-pulsed excimer laser. Our excimer-laserannealing (ELA) modeling capability is based on a standard finite-element CFD software package, which, however, has been modified to accommodate the specific demands of very rapid heating of thin Si films. In that sense, we've abandoned the traditional equilibrium formulation (i.e. enthalpy method), for phase-change computations, and have adopted a new approach that allows superheated solid and undercooled liquid to exist during the various stages of the heatinglcooling cycle. Our model has been successfully applied to predict the shape and temporal evolution of temperature profiles in the case of localized melting of silicon thin-films by excimer laser irradiation. Such scenario corresponds to conditions typically encountered in laser-induced lateral crystallization of a-Si films, a process that has recently attracted attention for the formation of high quality poly-Si films.
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