Current issues and problems in the chemical vapor deposition (CVD) of diamond are those which relate to its characterization, its nucleation on foreign surfaces, the question of its formation in preference to the other phases of solid carbon (for example, graphite, chaoite, or lonsdaleite), why different morphologies and crystallographic orientations (textures) are seen in different experiments or with different parameters in the same experiment, and finally whether well-crystallized metastable phases can be obtained by CVD in other material systems or are only a peculiarity of carbon chemistry. Whether a given carbon coating is justly described as diamond has been such an issue, and coatings should clearly show evidence for diamond by x-ray diffraction and Raman spectroscopy before the claim of diamond is made. Experimental results have not been consistent in many cases, and much work remains to be done before an accurate assessment can be made of the technological impact of the development.

https://science.sciencemag.org/content/sci/247/4943/688.full.pdf

Current Issues and Problems in the Chemical Vapor Deposition of Diamond

Generation of diamond nuclei has been realized on a silicon mirror surface in plasma chemical vapor deposition. Prior to the normal diamond growth process, a predeposition process of several minutes duration was introduced in which a high methane fraction in the feed gas was used and in which a negative bias voltage was applied to the substrate. This resulted in an enormous enhancement of the generation of diamond nuclei. For the onset of diamond nucleation the minimum voltage was −70 V and the minimum methane fraction in the methane‐hydrogen feed gas was 5%. Density of a diamond nuclei as high as 1010/cm2 was attained with this method.

Generation of diamond nuclei by electric field in plasma chemical vapor deposition

The stress in diamond films prepared by microwave plasma CVD was investigated as a function of methane concentration (0.2%–3.0%) and deposition temperature (600–900 °C). Tensile and compressive total (thermal and intrinsic) stress were observed, depending on the deposition conditions. The thermal stress is compressive and relatively constant (0.215–0.275 GPa) over the temperature range investigated. The intrinsic stress is tensile and its origin is interpreted in terms of the grain boundary relaxation model. Calculations indicate a value of 0.84 GPa, using the grain boundary model, which is in fair agreement with the measured value. For the methane series, the tensile intrinsic stress decreases with increasing the methane fraction. The increasing compressive stress is ascribed to increased impurity (hydrogen and nondiamond phase carbon) incorporation with increasing methane fraction. 15N nuclear reaction analysis shows a linear correlation between hydrogen in the film and methane in the supply gas while spectroscopic ellipsometry shows a direct correlation between optically absorbing nondiamond (sp2) carbon incorporation and methane. For the temperature series, the intrinsic tensile stress increases with deposition temperature. The increase is ascribed to decreasing sp2 C incorporation with temperature, as confirmed by spectroscopic ellipsometry measurements.

Intrinsic stress in diamond films prepared by microwave plasma CVD

Genesis of presolar diamonds: Comparative high-resolution transmission electron microscopy study of meteoritic and terrestrial nano-diamonds

Diamond, silicon carbide, gallium nitride, aluminum nitride, and boron nitride are currently under development for both electronic and optoelectronic semiconductor devices. Predictions based on their physical properties indicate that devices made from these materials should be far superior to currently available devices in high power, high frequency, and short wavelength applications. Yet actual device implementation requires that adequate materials processing technology exists. In this review, the current state of the art for producing semiconductor devices from these materials is evaluated, and recommendations for areas needing further research are outlined.

Prospects for device implementation of wide band gap semiconductors

Diamond synthesis from the vapor phase has been studied using hot filament assisted CVD, microwave plasma assisted CVD in an open system, and chemical transport process in a closed system using a gas mixture of hydrocarbon diluted with hydrogen gas. The deposited materials were identified as a cubic diamond with x-ray diffraction and Raman scattering measurement. The deposition process of diamond was considered on the basis of these experimental results and a review of the relevant field. The results suggest that the diamond synthesis proceeded by the deposition process, with the etching process operating simultaneously, and that atomic hydrogen played a very important role as the etching agent for non-diamond carbon. Also, the deposition process would be considered as the method that utilizes the bonding energy difference on each crystal surface of the diamond. The complicated problems on diamond synthesis originate from the fact that a third allotropic form exists in carbon, that is, the carbyne group.

Nobuo Setaka

Papers

Diamond synthesis from vapor phase and its growth process