Numerical Simulation And Study Of Resonant Cavities For Microwave Plasma Chemical Vapour Deposition

An important method currently used to prepare high quality diamond films is microwave plasma chemical vapor deposition(MPCVD),which is highly controllable during the deposition of diamond films,and this method produces diamond films with excellent quality and few inclusions.The most critical part of the technique is the design of the microwave resonant cavity.Numerical simulations and deposition experiments have been carried out to investigate this design process.Firstly,in the numerical simulations,different modes of cylindrical microwave resonant cavities used in established microwave vapor deposition devices were analyzed to investigate the electric field distribution within the cavity in different modes of operation,and the relationship between the electric field lines within the cavity and the cavity walls was analyzed according to resonant cavity theory.The initial dimensions of the cavity are obtained from the pure electric field distribution within the cavity and further optimized in a multi-physics field model to obtain the 2D cross-sectional dimensions of the microwave resonant cavity.Based on this design process,a new parabolic top high-power MPCVD resonant cavity with TM₀₂₁ mode and a parabolic shaped cavity MPCVD resonant cavity were designed at the simulation level and different experiments were designed in the multi-physics field model to verify the feasibility of these two types of microwave resonant cavities.Secondly,in the deposition experiments,the operation of the cylindrical microwave resonant cavity is verified by finite element analysis and the overall performance of the resonant cavity is predicted by simulation.Based on the resonant cavity dimensions derived from the simulation results,a cylindrical microwave resonant cavity with an electromagnetic field conditioning ring was constructed.The resonant cavity has a stable input frequency deviation in the range of 2.43GHz to2.47GHz.The addition of an EMF ring in the upper cavity reduces the return loss and thus improves the energy feed efficiency of the whole device,where the return loss can also be optimized by adjusting the air pressure to the input power and the distance between the short-circuiting piston and the antenna,which will help to improve the microwave utilization efficiency.The laboratory used a2.45GHz cylindrical microwave resonant cavity to deposit a diamond film on a 2-inch diameter silicon wafer and tested the morphology and quality of the diamond film using various characterization methods.The final experimental results show that high quality polycrystalline diamond films can be produced using this cylindrical MPCVD device.