Structural imperfections in CVD diamond films
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(Received 16 September 1988; accepted 9 February 1989) Microwave plasma assisted CVD diamond films have been studied by transmission electron microscopy. Cross-section TEM as well as plan-view TEM methods were used to investigate various structural defects formed in the films. It was found that diamond films contain a large number of stacking faults and twins which lie on the {111} planes in diamond. With an increase in methane concentration during the deposition process, the density of these defects increases and their dimensions become smaller. The tendency for forming these structural defects is of concern in developing tailored structures and properties of diamond films.
I. INTRODUCTION Considerable interest has been centered on the growth of diamond films by various deposition techniques. Little evidence is as yet available on structural imperfections present in the films, and these structural defects certainly have an important effect on properties of diamond films. It has been shown that natural diamond often has multiple-twinned morphology and that there are planar defects in the structure which are believed to be caused by the presence of nitrogen impurity.1 Walmsley and Lang found that twins and dislocations exist in high pressure/ high temperature grown diamonds.2 Matsumoto and Matsui reported that there are microtwins formed during CVD diamond film growth.3 These defects are closely related to process conditions. This paper reports on the structural defects of diamond films prepared by microwave plasma assisted chemical vapor deposition (MPACVD). The cross-section TEM method as well as the plan-view TEM method were used to reveal the internal structure of diamond films. The structural defects are correlated to deposition parameters in an effort to understand mechanisms of defect formation. Their influence on the properties of diamond films is discussed. II. EXPERIMENTAL Diamond films were deposited on {100} oriented single crystal silicon wafers in a tubular MPACVD system, as described previously.4 Details of the deposition conditions of samples are given with results. For the plan-view TEM observations, a 3 mm disk sample was ultrasonically cut from an as-grown film; then it was polished to 100 pim thick with 600 grit sandpaper from the substrate side and further thinned to 20 /Am with a dimpling machine; and finally it underwent argon ion milling until perforation occurred. The cross-section TEM sample preparation was more difficult, consisting of the following steps: two pieces (0.5 X 2 x 0.5 mm3) were sliced from a bulk sample with a wire saw; they were bonded together face-to-face; this bonded piece was put on a 3 mm titanium disk support which had a slot for its insertion; then J. Mater. Res., Vol. 4, No. 3, May/Jun 1989
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it was thinned in the same way as that described above for the plan-view TEM sample preparation. Because of large differences in sputtering rates among the diamond film, silicon substrate, and bonding glue, special precauti
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