Multiphysics Coupling Simulation and Structural Optimization of MPCVD Resonant Cavity for Diamond Thin Film Growth

doi:10.16553/j.cnki.issn1000-985x.2025.0261

Abstract

Abstract: Microwave plasma chemical vapor deposition （MPCVD） grown diamond thin film quality is dominated by process parameters and deposition apparatus. Taking a company’s MPCVD equipment as the research object， this study constructed resonant cavity simulation models via SolidWorks and COMSOL Multiphysics. Comparative analysis shows consistent electric field distribution between the two-dimensional axisymmetric and three-dimensional models. Based on the axisymmetric model， systematic plasma simulations were performed under varying power， pressure， and molybdenum stage height. Results show that increased input power flattens plasma distribution and significantly expands the excitation region above the deposition platform； higher pressure enhances plasma density but reduces cluster volume and distribution uniformity； a higher molybdenum stage also effectively improves plasma distribution uniformity. In this study， single-factor optimization was performed on the resonant cavity （overall and internal structure） to enhance plasma excitation efficiency and reduce heat dissipation pressure. This optimization results in an increase of the central electric field strength above the deposition stage to 473 276 V/m （26.4% higher than the pre-optimization value） and an 11.5% reduction in the coaxial segment’s secondary electric field strength. Based on single-factor optimization results， ten parameters were optimized via Box-Behnken design （BBD） and response surface methodology in this study， followed by a secondary optimization of four key factors. This multi-variable collaborative optimization further improves the central electric field strength by 5.5% compared to the single-factor optimization outcome， verifying the effectiveness of multi-variable collaborative optimization. This study provides theoretical support for MPCVD equipment parameter regulation， structural improvement， and process optimization.

Key words: microwave plasma chemical vapor deposition; resonant cavity; numerical simulation; uniformity; response surface methodology

CLC Number:

O782

LIU Benxue, CHEN Mingming, LI Xia, WANG Guanghui, FAN Yonghao, RONG Jinyue. Multiphysics Coupling Simulation and Structural Optimization of MPCVD Resonant Cavity for Diamond Thin Film Growth[J]. Journal of Synthetic Crystals, 2026, 55(5): 715-727.

Figures/Tables 18

Fig.1 Plasma distributions of domestic MPCVD equipment［8-10］

Fig.2 Diagrams of the MPCVD equipment and its structure

Fig.3 Schematic of model dimensions and boundary condition setup

Fig.4 Electric field distribution under initial conditions

Fig.5 Distribution of key parameters in the cavity under initial operating conditions.（a） Spatial distribution diagram of plasma；（b） electric field distribution diagram in the presence of plasma；（c） temperature distribution diagram of the reaction chamber；（d） electron temperature diagram

Fig.6 Plasma experimental and simulation results at different power levels

Fig.7 Plasma density curves under power gradients

Fig.8 Plasma experimental and simulation results at different pressures

Fig.9 Plasma density curves under pressure gradients

Fig.10 Plasma distribution under different molybdenum stage heights

Fig.11 Plasma density curves with varying molybdenum stage heights

Fig.12 Single-factor scanning results of resonator body structural parameters

Fig.13 Scanning diagrams of resonator internal structural parameters. （a） Height of quartz glassGH；（b） radius of guiding devicedl；（c） radius of deposition platformD；（d） thickness of deposition platformh

Table 1 Levels of 4 factors for BBD sampling

Factor	Specific name	Reference value/mm	Minimum value/mm	Maximum value/mm
A	RadiusR₁	106.4	105.7	107.1
B	HeightH₂	102.0	101.8	102.2
C	HeightH₃	14.45	14.25	14.65
D	RadiusR₃	148.5	144.0	153.0

Table 2 Fitted statistical metrics for 4 factors impact

Coefficient of determination （R²）	0.991 4
AdjustedR²	0.982 7
PredictedR²	0.950 2
Adequate precision	24.471 9

Fig.14 Interaction effect diagrams of various factors on the response variable

Table 3 Optimization scheme based on response surface method

Optimization scheme	1st	2nd	3rd
Radius，R₁/mm	106.584	106.581	106.590
Height，H₂/mm	102.022	102.024	102.020
Height，H₃/mm	14.250	14.250	14.250
Radius，R₃/mm	151.295	151.288	151.310
Predicted value/（V·m^-1）	491 229	491 229	491 228
Simulated value/（V·m^-1）	498 937	498 964	499 261
Error/%	1.57	1.57	1.64

Fig.15 Comparison of electric field intensity before and after optimization

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