Numerical simulation and experiment of uniform growth of MPCVD diamond coating
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摘要: 基于多物理场耦合仿真软件COMSOL Multiphysics的微波等离子体模块建立MPCVD反应腔内氢气等离子体的仿真模型,研究基底外侧增设的环状钼支架与基底的不同高度差Δh对基底表面等离子体分布的影响。采用变异系数对等离子体分布的均匀性进行定量分析,并用SEM对金刚石涂层表面的微观形貌进行表征。结果表明:当Δh=0 mm时,等离子体分布的均匀性最佳,变异系数为3.998%,金刚石涂层的晶粒分布及大小的均匀性相较于无钼支架时的明显提升;当Δh<0 mm时,等离子体分布的均匀性随Δh增大而提升,变异系数由10.265%降至3.998%;当Δh>0 mm时,等离子体分布的均匀性不增反降,变异系数升高至10.048%。此外,当Δh=−2.0 mm时,基底表面的等离子体密度约下降20%,不利于金刚石涂层生长。Abstract: Based on the microwave plasma module of multiphysics simulation software COMSOL Multiphysics, a numerical model of hydrogen plasma inside a MPCVD reactor was built. The effect of different height differences Δh between the circular molybdenum support added on the outer side of the substrate and the substrate on the plasma distribution at the surface of the substrate was investigated. The uniformity of plasma distribution was quantitatively analyzed by coefficient of variation, and the microstructure of diamond coating surface was characterized by SEM. The results show that when Δh=0 mm, the uniformity of plasma distribution is the best, the coefficient of variation is 3.998%, and the uniformity of grain distribution and size of diamond coating is significantly improved compared with that without molybdenum support. When Δh< 0 mm, the uniformity of plasma distribution increases with the increase of Δh, and the coefficient of variation decreases from 10.265% to 3.998%. When Δh>0 mm, the uniformity of plasma distribution does not increased but decreases, and the coefficient of variation increases to 10.048%. In addition, when Δh=−2.0 mm, the plasma density on the substrate surface decreases by about 20%, which is not conducive to the growth of diamond coating.
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Key words:
- diamond coating /
- uniformity /
- microwave plasma /
- numerical simulation
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表 1 原始数据及电子数密度的变异系数
Table 1. Original data and coefficients of variation of electron number density
高度差 Δh / mm 标准差 $\sigma $/ m−3 平均值 $\mu $/ m−3 变异系数 ${C_{\rm{v}}}$/% −2.0 3.918 × 1017 3.817 × 1018 10.265 −1.0 2.842 × 1017 3.801 × 1018 7.477 −0.5 2.233 × 1017 3.649 × 1018 6.119 0 1.516 × 1017 3.792 × 1018 3.998 0.5 1.504 × 1017 3.497 × 1018 4.301 1.0 3.131 × 1017 3.116 × 1018 10.048 表 2 实验工艺参数
Table 2. Process parameters
参数 形核 生长 基底温度 θ / ℃ 625 800 CH4流量 l1 / sccm 5.0 4.3 CO2流量 l2 / sccm 6.0 0 Ar流量 l3 / sccm 15 0 H2流量 l4 / sccm 200 200 压力 p / kPa 8 8 时间 t / h 2 7 表 3 沉积前后基底厚度
Table 3. Substrate thickness before and after deposition
测量区域 实验前厚度
d1 / mm沉积后厚度
d2 / mm厚度差
Δd / μm对照组基底中心 2.001 2.033 32 对照组基底边缘 2.006 2.044 38 实验组基底中心 1.997 2.021 24 实验组基底边缘 2.002 2.028 26 -
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