Homoepitaxial Growth of Diamond by an Advanced Hot-Filament Chemical Vapor Deposition Method

Eiichi Kondoh, Kenji Tanaka and Tomohiro Ohta

Homoepitaxial (111), (110), and (100) diamond films were grown by an advanced hot-filament chemical vapor deposition method that enables accurate control of the substrate temperature independently of the other CVD parameters. The obtained films were exmained mainly by optical microscopy and reflection high energy electron diffraction (RHEED). The surface morphology of the films depended on the deposition pressure, methane concentration in the feed gas, and substrate temperature. Very streaky RHEED patterns, indicative of atomically smooth surfaces, were obtained from the samples deposited on the (111) substrates at a pressure of 100-500Torr and methane concentration of 0.5%, and also from the samples deposited on the (100) substrates at 300-500Torr and 1-2%. These conditions, which we call `window' conditions, are remarkable, since such deposition pressures as 100-500Torr are much higher than the few tens of Torr normally required for polycrystalline growth. However, the films on the (110) substrates exhibited spotty patterns due to 3-dimensional growth, although optical-microscopically smoothness was achieved by the 500Torr and 0.5% deposition. Regarding the pressure effects, a reduction of H radicals and concurrent increase of the C2Hx (x=1-2) species are characteristic of the gas-phase chemistry under these window conditions. We speculate that the success of epitaxial deposition under these window conditions was due to surface reconstruction arising from the lack of H radicals and/or from the surface reactions in which C2Hx mediates.

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