Promoting secondary nucleation using methane modulations during diamond chemical vapor deposition to produce smoother, h
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In this paper, we present results obtained from a comparison study relating to the deposition of diamond films using two processes, namely, time-modulated chemical vapor deposition (TMCVD) and conventional CVD. Polycrystalline diamond films were deposited onto silicon substrates using both hot-filament CVD and microwave plasma CVD systems. The key feature of TMCVD is that it modulates methane (CH4) flow during diamond CVD, whereas in conventional CVD the CH4 flow is kept constant throughout the deposition process. Films grown using TMCVD were smoother, harder, and displayed better quality than similar films grown using constant CH4 flow during CVD. The advantage of using TMCVD is that it promotes secondary nucleation to occur on existing diamond crystals. Pulsing CH4, consecutively, at high and low concentrations allows the depositing film to maintain its quality in terms of diamond-carbon phase. Films grown under constant CH4 flow during diamond CVD displayed a columnar growth mode, whereas with the time modulated films the growth mode was different. The mechanism of film growth during TMCVD is presented in this paper. The growth rate of films obtained using the hot filament CVD system with constant CH4 flow was higher than the growth rate of time modulated films. However, using the microwave-plasma CVD system, the effect was the contrary and the time-modulated films were grown at a higher rate. The growth rate results are discussed in terms of substrate temperature changes during TMCVD.
I. INTRODUCTION
Diamond has many extreme properties that make it suitable for many potential applications in industry.1–3 Chemical vapor deposition (CVD) is a technology widely used to deposit diamond coatings onto a wide range of substrate materials.4–6 However, the difficulty in depositing truly superior diamond coatings is nearly as extreme as the material’s outstanding properties. Diamond films deposited using conventional hot-filament CVD (HFCVD) and microwave plasma CVD (MPCVD) systems, where CH4 and hydrogen are used as the precursor gases, tend to exhibit high surface roughness mainly due to the columnar growth of the nonorientated polycrystalline diamond films.7 One of the major limitations of the wide scale use of diamond coatings has been the high roughness of the films. As a result, this has severely hampered diamond coatings’ widespread use in microelectronics, biomedical, and optical applications. A number of researchers have endeavored to control the
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J. Mater. Res., Vol. 18, No. 2, Feb 2003 Downloaded: 03 Apr 2015
microstructure and the morphology of diamond films to produce smoother looking diamond films. There are three noteworthy methods used to control film surface roughness and morphology, (i) nucleation methods, e.g., bias-enhanced nucleation, 8 (ii) growth conditions, e.g., nitrogen doping,9 and (iii) postdeposition treatment, such as laser and mechanical polishing, which have been reviewed elsewh
