| dc.description.abstract | Metal organic chemical vapor deposition(MOCVD) has good epitaxy film uniformity and is suitable for mass production. It is the main fabrication process for the LED. MOCVD equipment, the source gas inlet system is very critical. The close coupled showerhead(CCS) is one the important inlet system design. It uses multiple holes, to make the flow uniform and stable, and thus increase uniformity of the deposit film. The process has large processing margin and can reduce the amount of the metal organic compound. The CCS design, however, is easy to cause clogging of the inlet orifices. In this thesis, we numerical simulate the clogging rate of the orifices of a CCS reactor due to adsorption of the reactive species. The simulation takes accounts of fluid dynamics, heat and mass transports, and chemical reactions, and the flow, temperature, and species distributions are obtained. The deposition rate and the adsorption rate then can be calculated to evaluate the deposition performance and the clogging degree. Finally, a modified inlet system design is proposed.
In the study, we first, consider the flow rate effects on the inlet nozzle adsorption rate. It is found that the higher proportion of TMG in the inlet gas source, the higher the adsorption rate at the inlet nozzle and the higher the growth rate at the susceptor. When the flow rate increases, the adsorption rate at inlet nozzle decreases, but the growth rate at susceptor enhances. Furthermore, the results show the main species causing nozzle clogging is TMGNH3.
In the inlet nozzle design, the chamfered nozzle and the concentric nozzle designs are studied. In the case of the chamfered nozzle, the growth rate on the susceptor reduces 0.4%, while the adsorption rate at the nozzle reduces 5.3%. The effectiveness of using chamfers are not remarkable. In the concentric inlet design, it is found that the adsorption rate at the nozzle reduces 36.3%, while the growth rate on the susceptor decreases 22.6% due to the dilution of additional H2. Also, the growth rate near the symmetry axis becomes less uniform. By adjusting the flow rate of the H2 in the concentric nozzles, the situation can be alleviate. Overall, the concentric inlet nozzle design is promising in reducing the nozzle clogging. | en_US |