Edge effect during microwave plasma chemical vapor deposition diamond-film: Multiphysics simulation and experimental verification

This study focused on the investigation of the edge effect of diamond films deposited by microwave plasma chemical vapor deposition. Substrate bulge height is a factor that affects the edge effect, and it was used to simulate plasma and guide the diamond-film deposition experiments. Finite-element software COMSOL Multiphysics was used to construct a multiphysics (electromagnetic, plasma, and fluid heat transfer fields) coupling model based on electron collision reaction. Raman spectroscopy and scanning electron microscopy were performed to characterize the experimental growth and validate the model. The simulation results reflected the experimental trends observed. Plasma discharge at the edge of the substrate accelerated due to the increase in Δh (Δh = 0–3 mm), and the values of electron density (n_e), molar concentration of H (C_H), and molar concentration of \(\text{CH}_{3} \ (C_{\text{CH}_{3}})\) $${\text{CH}}_3(C_{{\text{CH}}_3})$$ doubled at the edge (for the special concave sample with Δh = −1 mm, the active chemical groups exhibited a decreased molar concentration at the edge of the substrate). At Δh = 0–3 mm, a high diamond growth rate and a large diamond grain size were observed at the edge of the substrate, and their values increased with Δh. The uniformity of film thickness decreased with Δh. The Raman spectra of all samples revealed the first-order characteristic peak of diamond near 1332 cm⁻¹. When Δh = −1 mm, tensile stress occurred in all regions of the film. When Δh = 1–3 mm, all areas in the film exhibited compressive stress.