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Ion-bombardment-induced heteroepitaxy and texture in diamond films

: Klages, C.-P.; Jiang, X.; Paul, M.; Xia, Y.B.; Zhang, W.J.

Sato, Y. ; National Institute for Research in Inorganic Materials -NIRIM-, Tokyo:
Advanced materials '97. Proceedings of the 4rd NIRIM International Symposium on Advanced Materials
Tokyo: Int. Communication Specialists, 1997
ISBN: 4-944122-02-0
International Symposium on Advanced Materials (ISAM) <4, 1997, Tsukuba>
Conference Paper
Fraunhofer IST ()
Bias; Diamant; diamond; Heteroepitaxie; heteroepitaxy; Textur; texture

Heteroepitaxial nucleation of diamond from the gas phase can be achieved on silicon substrates and on single-crystalline cubic silicon carbide (3C-SiC) wafers by applying a negative substrate bias voltage during a microwave plasma CVD process. By continuing film growth under conventional growth conditions after a suitably chosen nucleation step, highly ordered heteroepitaxial films can be obtained in which virtually all crystallises have lost three degrees of orientational freedom by aligning their lattice planes parallel to the corresponding lattice planes of the substrate single crystal. Progress in optimization of growth conditions has meanwhile lead to a decrease of the residual rotational tilt and twist disorder in heteroepitaxial films to the order of one degree. Investigations of the mechanism of bias-induced heteroepitaxial nucleation lead to the conclusion, that the effect is due to a substrate bombardment by carbon-bearing ionized species with kinetic energies of roughly 100 eV and not due to some changes in the gas phase chemical composition in the vicinity of the substrate. In case of epitaxy on silicon (001), high-resolution TEM studies of the substrate / diamond film interface reveal well defined interface structures and defined orientation relationships of grains grown directly on the clean silicon surface. The benefits of a heteroepitaxial ordering of diamond films are - among increased surface smoothness at small film thicknesses as compared to random films - improved mobilities of electrical charge carriers and possibly better thermal conductivities at moderate film thicknesses. Another phenomenon induced by applying a substrate voltage continuously during film growth was recently observed at FhG-IST: As a consequence of the ion-flux towards the wafer [001]-oriented diamond films could be grown on polycrystalline or [111]-textured diamond films serving as substrates. The reason for this observation is most probably a very selective orientational de pendence of reactive ion etching by H+ ions bombarding the substrate: SEM studies show that the etching is considerably more pronounced on non-[001] oriented grains than on grains with a (001) face parallel to the substrate surface. Therefore, utilizing these observations, bias-induced [001]-texturing of diamond films is possible. On the other hand, the quality of heteroepitaxial films can be improved by applying H+ etching phases intermittingly during the growth process.