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B. R. Stoner Kobe Steel USA Inc., Electronic Materials Center, Research Triangle Park, North Carolina 27709 (Received 21 October 1993; accepted 3 June 1994)

Highly oriented diamond thin films grown on silicon via microwave plasma chemical vapor deposition were examined by transmission electron microscopy. In the plan view, defects appearing at the grain boundary were easily observed. (100) faceted grains that appeared to have coalesced were connected at their interfaces by dislocations characteristic of a low angle grain boundary. From Burgers vector calculations and electron diffraction patterns, the azimuthal rotation between grains was measured to be between 0 and 6°. The defect densities of these films are compared to reports from (100) textured randomly oriented films, and the relative improvement due to the reduction of misorientation and grain boundary angles is discussed.

Diamond thin films are attractive for numerous applications involving electronic devices in extreme environments due to several unique properties.1 At the moment, this goal is limited by the unavailability of low-cost single crystal diamond; however, synthetic diamond grown via chemical vapor deposition (CVD) has produced highly oriented polycrystalline diamond2"4 which may be sufficient quality to address certain electronic properties. However, a major issue for these oriented polycrystalline films will be the effect of grain boundaries on the resulting electronic properties. Ideally, defects, grain boundaries, and roughness will be minimized such that the film properties approach those of single crystal. Structural information regarding the grain boundaries and associated defects could lead to a greater understanding of the basic growth mechanisms and the resulting electronic properties of highly oriented diamond films. Transmission electron microscopy (TEM) is a powerful tool for understanding such defects and grain boundaries. Previous TEM work in diamond has given insight into the diamond/substrate interface5"11 and defects both within the grains and at the grain boundaries.12"16 However, no TEM studies to date have been reported on highly oriented diamond films consisting of epitaxially oriented grains. The (100) oriented diamond films used for these experiments were grown on (100) silicon via bias-enhanced microwave plasma chemical vapor deposition (MPCVD) using a three-step growth process, details of which have been previously reported.2 Plan view TEM was conducted with the transmitted beam parallel to the [001] direction. Sample preparation of these films used a standard technique of polishing and dimpling followed by ion milling until penetration through the film.6 J. Mater. Res., Vol. 9, No. 10, Oct 1994

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A TOPCON 002B high resolution microscope operated at 200 kV and a Hitachi H-800, also operated at 200 kV, were used for these samples. The TOPCON 002B was chosen for its high magnification and microdiffraction capabilities which permitted diffraction pattern imaging from