Flux profile modeling using Monte Carlo simulation

Molecular beam Epitaxy (MBE) is a process by which semiconductor films are grown on the substrate by physical vapor deposition of the source material in an ultra high vacuum environment. Spatial variations in flux are a result of the shape of the crucible and the geometry of the growth chamber. In this study a process simulation tool for MBE based on a phenomenological model is proposed and elaborated.; Two different models based on physical principles are investigated. Model I includes the primary flux from the liquid surface and a secondary flux re-emitted from the crucible walls for the total flux at the platen. No intermolecular collisions are considered in this model. Since the investigated 10000g SUMO crucible has a tapered region leading to the crucible opening (smallest radii opening), molecules undergo extensive interwall and intermolecular collisions in that region. Simulation of intermolecular collisions requires considerable time and limits the usage of the modeling tool in the industry. Thus, the effect of intermolecular collisions is captured through the assumption of a virtual flux source (VFS) at the neck in model II. For the two models, the simulation is performed using the Monte Carlo approach. The results of model II obtained from using cos2theta distribution from the VFS, best describes the experimental data for the SUMO 10000g crucible.; Thus the tool is capable of simulating flux effusion for different crucibles and geometries once the nature of distribution from the crucible is established. The accurate description of the distribution can be obtained by changing the distribution parameter and comparing the generated profiles with experimental results. (Abstract shortened by UMI.)...