Effect of methane concentration on the growth kinetics, microstructure, and crystalline quality of thick MPCVD-grown polycrystalline diamond

Abstract

In diamond growth using microwave plasma chemical vapor deposition (MPCVD) process, the methane fraction controls the balance between carbon supply and hydrogen etching, while substrate temperature governs surface diffusion and facet‑dependent growth. Yet for polycrystalline diamond (PCD) films used as optical windows and heat spreaders, the combined influence of these two parameters is rarely quantified across multiple, cross‑validated metrics. Here we isolate the role of CH₄ at fixed temperature by growing PCD on identically prepared Si (100) wafers with all parameters held constant except the methane fraction (4 to 8% at 890 °C). In addition, at a fixed CH₄ concentration of 4%, the growth temperature was varied from 840 °C to 890 °C. Freestanding films with thicknesses of ~ 190–325 μm were obtained, enabling correlation of growth kinetics with texture, grain coarsening, and defect content. Raising temperature from 840 °C to 890 °C at 4% CH₄ more than doubled the growth rate and strengthened a (220) preferred orientation. At 890 °C, increasing CH₄ from 4% to 6% maximized the growth rate (~ 2.8 μm h^− 1) but increased sp² signatures (Raman I₁₄₅₀/I₁₃₃₂), the SiV-related emission intensity ratio (I₂₂₅₀/I₁₃₃₂) and broadened the diamond FWHM; at 8% CH₄ the lattice disorder and non‑diamond carbon rose sharply (FWHM ≈ 5.86 cm^− 1) with partial loss of (220) texture. These results define a practical window characterized by high temperature with moderate CH₄ where thick PCD attains a useful trade‑off between deposition rate and crystalline quality for device‑relevant components.