Effect of microwave electric field displacement on diamond deposition in microwave plasma chemical vapour deposition: a three-dimensional simulation study

The investigation of the uniform deposition of large-area, high-quality diamond thick films has been a prominent focus of related research. Herein, a three-dimensional simulation of the microwave plasma chemical vapour deposition (MPCVD) reactor was conducted using the finite element method, with a three-dimensional (3D) model replicating the actual reactor dimensions built in COMSOL software. By analysing the 3D microwave electric field distribution within the resonant cavity, along with the S₁₁ dB parameter related to port reflection, the influence of resonant cavity anharmonicity on microwave plasma deposition of large-area diamond was examined. The deflection and misalignment of the annular cone antenna at the top of the resonant cavity alter its intrinsic frequency, disrupting the optimal resonance between the microwave and the cavity. Consequently, the waveguide transitions from an axially symmetric transmission mode to a non-axially symmetric one, resulting in variations in the microwave electric field distribution under the influence of the substrate holder within the cavity. Based on actual feedback from the diamond film deposition process, precise optimisation of the resonant cavity’s top structure can significantly reduce irregularities in the microwave electric field distribution. This allows for better concentration of maximum field strength at the intended central position and minimises the effects of anharmonicity. This study offers theoretical support for further enhancing the uniform deposition of large-area diamond thick films in MPCVD systems.