(110)-oriented diamond films synthesized by microwave chemical-vapor deposition

Bilayer diamond films were deposited on Si substrates by microwave-plasma chemical-vapor deposition (CVD) using a methane-hydrogen gas mixture. The first layer was deposited for 3 h using a reaction gas which was composed of 2.5 vol. % methane and 97.5 vol.% hydrogen. The deposited film consisted of very weakly (110)-oriented microcrystalline diamonds as well as amorphous carbon and graphite. In order to remove non-diamond carbons from the film surface, the specimen was treated in hydrogen plasma for 1 h. Finally, a second layer was deposited on the first layer for 14 h using a methane concentration of between 0.2 and 1.6 vol.%. It was found that the x-ray intensity of the (220) diffraction of the bilayer films was much greater than that of the (111) diffraction, indicating that the diamond grains in the second layer were strongly oriented with their crystallographic (110) planes parallel to the substrate surface. X-ray diffraction spectra of bilayer films in which the second layer was deposited for 7, 14, 21, and 35 h using two different methane concentrations, 0.3 and 1.2 vol.%, showed that within periods of up to 21 h, the (220) intensity increased with the deposition time much more quickly than the (111) intensity, indicating that the degree of (110) orientation was further enhanced as the second layer thickness increased. However, the (220) intensity decreased after 21 h, presumably due to thermal randomization. Results of scanning electron microscopy, electron diffraction, and Raman spectroscopy of the bilayer films are also presented.