Numerical Study On Transport Phenomena In A Radial Flow MOCVD Reactor With Three-Separate Vertical Inlets

Metalorganic chemical vapor deposition (MOCVD) is a key technology in the manufacturing of micro-electronics and photoelectronics including laser and microwave devices. After 30 years' development, MOCVD technology plays a critical role in today's semiconductor industry. In CVD reactors there exist complex transport phenomena (i.e. fluid flow, heat transfer and mass transfer) along with the physical and chemical processes. Large temperature and concentration differences taking place in CVD process lead to natural convection and concentration diffusion which interact with forced convection and complex reactor geometries. In addition, there exist chemical reactions of gas phase and surface, thermal diffusion caused by large thermal gradient, the radiative heating of substrate to wall and so on. All these phenomena are coupled together and affect film growth rate and quality. Thus, to improve the film quality and to optimize the reactor geometry, it is important to have a detailed understanding of transport process in CVD reactor.Planetary reactor is a newly-developed reactor which has been used widely. It has two-separate vertical inlets from which gases enter vertically and then flow radially outwards. Each wafer makes a planetary rotation so that to achieve an uniform concentration above the substrate.. Two separate inlets avoids unwanted pre-reactions before deposition. This kind of reactor is suitable for large-scale production. At present, studies on this reactor have been limited to fixed commercial reactor structure and growth processes with limited variations of operating parameters. In this thesis, we carried out a detailed numerical modelings on the transport process of a planetary reactor with three-separate inlets designed by ISCAS with the help of FLUENT code. We also explore the possibility to optimize the transport process as well as the reactor.By varying the operating parameters (such as inlet flow rate, temperature, pressure, etc.) and reactor geometry, we explore how they affect transport phenomena. It is found that recirculation cells due to natural convection and sudden expansions in the flow cross-sectional area can be reduced by increasing the flow rate of mid tube, reducing the pressure, lowering the temperature difference between substrate and the top wall, inverting the reactor, reducing the height between the substrate and top wall, and so on. Rotating the susceptor with high speed results in stronger recirculations. By modifying the reactor geometry into streamlined shape, the recirculation cells can be reduced even eliminated. It is found that among all the parameters that affect thermal convection, the height of the reactor chamber plays a leading role while the diameter of chamber does not. It is also found that uniform flow fields correspond to uniform temperature field and higher susceptor concentration. At last, we simulate Benard convection within the MOCVD reactor. It is found that the critical Ra number is larger than predicted by current theory.