Optimization of Growth Parameters for Diamond Films Grown by MPCVD Using Response Surface Methodology

Diamond films were synthesized by microwave plasma chemical vapor deposition under different deposition parameters. Response surface methodology was adopted to guide the optimization of synthesis parameters including the substrate temperature (716–884 ∘C)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${^{\circ}{\rm C})}$$\end{document}, gas pressure (4.32–7.68 kPa), and volume concentration of methane to hydrogen (1.3–4.7 %) for deposition of the films. A 5-level-3-factor central composite design was employed to evaluate effects of the deposition parameters on the response (growth rate and pure index). The significant level of both the main effects and the interaction is investigated by analysis of variance. With its assistance, the growth quality of the obtained samples was improved dramatically. The structure, surface morphology and growth rate of films were characterized by X-ray diffractometer and scanning electron microscopy. The diamond phase content of films was investigated using Raman spectroscopy and X-ray photoelectron spectroscopy. The optimum substrate temperature, gas pressure, and volume concentration of methane to hydrogen were found to be 837 ∘\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${^{\circ}}$$\end{document}C, 6.95 kPa and 2 %, respectively. Under this experimental condition, the growth rate and pure index of diamond films were 0.378 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mu}$$\end{document}m/h and 4.092, which are quite good correlation with value (0.383 μ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mu}$$\end{document}m/h and 4.182) predicted by the model. The diamond phase content of the films is 89.5 %.