Numerical Study On Transport Phenomena In A MOCVD Reactor With Tangential Inlets

Metalorganic chemical vapor deposition(MOCVD) is a key technique in the manufacturing of microelectronics and photoelectronics devices.In MOCVD reactors there exist large temperature and concentration differences,which will lead to intense natural convection and concentration diffusion that interact with forced convection and complex reactor geometries.In addition,there are chemical reactions of gas phase and surface,thermal diffusion caused by large thermal gradient and the radiation heat-exchange from substrate to wall.All these phenomena are coupled together and affect film growth rate and quality.Thus,to optimize the reactor geometry,control the film growth rate and improve the film quality,it is important to have a detailed understanding of transport processes in MOCVD reactors.Suggested by the Rotation Disc Reactor and the improved horizontal reactor, author proposes a novel MOCVD reactor with tangential inlets.In the reactor the reactants are sprayed from the tangential inlets located equally around the wall,and the outlet is located in the center axis.Hence,a controlled vortex flow is obtained,and the reactants above the substrate are being rotated and accelerated.By compensating the loss of reactants running from inlets to outlet,it will help to get the uniform deposition.To validate the performance of the new-style reactor,we carried out a detailed numerical simulation on the transport process of this reactor with the help of FLUENT code.The objects of the numerical simulation include a fundamental three-dimension model,a three-dimension model containing radiation effect and a three-dimension full-scale model with chemistry reaction.By varying the geometry and operation parameters,the performance of the reactor is investigated.We summarize:The natural convection can be restrained in the new reactor.The angle of inlets is a key to control the figure of the vortex flow.With outlet at the bottom of reactor can help to restrain parasitic reaction.To achieve big temperature gradient above susceptor and expedite growth rate,we can increase the standard flux of inlet or increase the number of inlets.Some optimized parameters are also explored.By compare the effect of both novel tangential reactor and common vertical reactor, novel reactor shows a more uniform temperature,velocity and concentration distributions above the substrate.After using Discrete Ordinate Method for radiation simulation,it shows that the temperature of the wall of the novel reactor cannot be kept under a low degree until the outer convective transfer coefficient reach about 160W/m~2-K.The reactor also shows an uniform growth rate with high utilization of reactants after the simulation of both gas phase and surface reaction of gallium nitride.At last,we conduct numerical simulations about GaN MOCVD on a commercial showerhead reactor.Some conclusions are found out:Increasing the flux of TMGa leads to higher growth rate of GaN,but lower utilization of TMGa.Increasing hydrogen or pressure leads to lower growth rate.Increasing the ammonia or the temperature of the susceptor makes the growth rate first increase and then decrease. High rotation speed results in high growth rate.The author also gives the explanations with the help of current literature.