Flux profile modelling using numerical methods
Molecular beam Epitaxy (MBE) is a physical vapor deposition system, used to grow semiconductor layers (epilayers). In order to increase the economics of MBE, the industry has increased the size and number of wafers processed in one stage. This lead to, non-uniformity in thickness of material grown. In this work a process simulation tool based on numerical methods was developed to study different parameters which affect the thickness. The process of emission in open cells was identified as free evaporation and for computer simulation of these types of cells Model I was developed. The process of emission in closed cells with orifice was identified as Knudsen effusion and for computer simulation of these types of cells Model II was developed. The cosine law of effusion was modified to account for the focusing effect exhibited by the industrial cells. The modified law involves parameter N and as N increases the focusing effect increases. The experimental data for 10,000G SUMO cell are in good agreement with the results of Model II for modifying parameter N = 1.9. From the study of different parameters it is observed that for the GEN 2000 MBE equipment which use 10,000G SUMO cell, if the angle of tilt is increased from 45Ã‚Â° to 52Ã‚Â° the flux variation reduces from 3.67% to 0.45%.
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