Edge effect during MPCVD diamond film deposition: multi-physics simulation and experimental verification

The edge effect of diamond films deposited by microwave plasma chemical vapor deposition (MPCVD) was investigated. As a factor that affects edge effect, substrate bulge height ∆h is used to simulate plasma and to guide the diamond film deposition experiments. Using the finite element software COMSOL Multiphysics, a multi-physics (electromagnetic field, plasma field and fluid heat transfer field) coupling model based on electron collision reaction was constructed. The experimental growth provided model validation by characterizing it using Raman spectroscopy and scanning electron microscopy. The simulation results reproduced the experimental trend. The increase in ∆h (∆h = 0−3 mm) accelerates the plasma discharge at the edge of the substrate, and the electron density (n_e), molar concentration of H (C_H), and molar concentration of CH3 (C_(〖CH〗_3 )) are doubled at the edge. (For the special concave sample with ∆h = −1 mm, the molar concentration of active chemical groups decreased at the edge of the substrate.) When ∆h = 0−3 mm, a higher diamond growth rate and a larger diamond grain size are obtained at the edge of the substrate in the experiment, which increases with ∆h. The film thickness uniformity decreased with ∆h. The Raman spectra of all samples show a first-order characteristic peak of the diamond, which was located near 1332 cm−1. When ∆h = −1 mm, all regions in the film experienced a tensile stress. When ∆h = 1−3 mm, all areas in the film show a compressive stress.