Development of flat, smooth (100) faceted diamond thin films using microwave plasma chemical vapor deposition
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Development of flat, smooth (100) faceted diamond thin films using microwave plasma chemical vapor deposition Andrew L. Yee,a) H. C. Ong, L. M. Stewart, and R. P. H. Chang Department of Materials Science and Engineering, Northwestern University, 2225 North Campus Drive, Evanston, Illinois 60208 (Received 6 December 1995; accepted 24 March 1997)
A novel approach has been used to develop (100) faceted diamond films with flat, smooth surfaces. A morphological study of the early stages of growth behavior of (100) homoepitaxial films versus process temperature and methane percentage was carried out using atomic force microscopy. The results showed that spiral growth features and penetration twin density were dominant for growth conditions not well suited for (100) growth. Optimized process parameters were found to proceed via a step mechanism consistent with ledge growth on (2 3 1) reconstructed (100) diamond surfaces. These optimized conditions were then applied to growth of polycrystalline diamond on pretreated silicon substrates. A unique octahedral faceted film resulted, indicating strong preference for growth in the k100l direction. Scanning electron microscopy, x-ray diffraction, and Raman spectroscopy were used to assess film morphology, internal fiber texture, and carbon phase, respectively. A second stage growth step was used to flatten the surface topography to achieve the desired (100) flat tile-like morphology. This smooth (100) surface exhibited enhanced tribological performance compared to a typical randomly textured diamond film.
I. INTRODUCTION
With the advent of the synthesis of diamond thin films using chemical vapor deposition methods came the promise of tapping into many of bulk diamond’s unique material properties. Unfortunately, due to the polycrystalline nature of diamond thin films, many of these properties (i.e., mechanical, thermal, electrical, and optical) are severely compromised. In order to maximize the performance of diamond films, strict control of their morphological development is of utmost importance. There have been previous studies that reported on the morphology of diamond thin films as a function of process parameters, namely hydrocarbon percentage and growth temperature.1–3 The observed trends revealed that higher hydrocarbon percentages and lower substrate temperatures favored growth of (100) faceted films, while opposite conditions yielded (111) faceted films. Though fabrication of polycrystalline diamond films with smooth faceted morphologies has been discussed in the literature,4–6 a full explanation of a step by step systematic approach to obtain such films has been lacking. Therefore, the focus of this report is to describe a methodology by which diamond thin films with smooth, flat (100) tile-like morphologies may be grown. There are several barriers that make this endeavor arduous. Even though morphology versus process parama)
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