Growth of diamond thin films by microwave plasma chemical vapor deposition process
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Growth of diamond thin films by microwave plasma chemical vapor deposition process H. C. Barshilia, B. R. Mehta, and V. D. Vankar Thin Film Laboratory, Department of Physics, Indian Institute of Technology, New Delhi-110 016, India (Received 8 June 1995; accepted 2 October 1995)
A very high vacuum compatible microwave plasma chemical vapor deposition system has been fabricated for the growth of diamond thin films. Microcrystalline diamond thin films have been grown on silicon substrates from the CH4 –H2 gas mixture. Scanning electron microscopy and x-ray diffraction have been used to study the surface morphology and the crystallographic structure of the films. Optical emission spectroscopy has been used for the detection of chemical species present in the plasma. The strong dependence of the film microstructure on the intensity of CH emission line has been observed.
I. INTRODUCTION
Diamond is one of the most valuable materials found in nature. The interest in diamond arises from its unique properties, viz., extreme hardness, high thermal conductivity, optical transparency over a wide wavelength range, and very high electrical resistivity.1–5 With the development of various low-pressure techniques for growing diamond thin films, it has become possible to use these coatings for a variety of applications, e.g., wear resistant coatings for cutting tools, heat sinks for high power devices, impact resistant coatings for high-density computer disks, protective coatings for IR optics, etc.6 Microwave plasma chemical vapor deposition (MWPCVD) is the most widely used technique to grow diamond thin films.7–10 Various hydrocarbon gases, e.g., CH4 and C2 H2 diluted with H2 , are being used to deposit these films. The growth conditions in the microwave plasma are distinctly different from those for the usual physical and chemical vapor deposition processes.4 The thermodynamics, kinetic behavior, and chemical composition of CH4 –H2 plasma are, however, not fully understood. The exact mechanism by which diamond growth occurs and the role of various process parameters is still a matter of controversy. The microstructure and properties of the films are found to be very sensitive to the various species present in the plasma. In order to understand the nucleation and growth of diamond films, a better understanding of the role of these plasma species is very important. There have been several attempts to diagnose chemical species in the plasma using optical emission spectroscopy (OES) in the diamond deposition process.11–16 OES is a nonperturbative technique used to detect lightemitting reactive species in the plasma. Complemented by other techniques like mass spectrometry, OES may lead to an understanding of the relationship between J. Mater. Res., Vol. 11, No. 4, Apr 1996
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the plasma chemistry, the microstructural, and electronic properties of the films. Although the emission spectroscopy does not provide directly the information a
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