Method of plasma enhanced chemical vapor deposition of diamond using methanol-based solutions

#The present disclosure relates to a method of synthesizing diamond. In particular, the present disclosure relates to a method of synthesizing diamond crystals and diamond films using plasma enhanced chemical vapor deposition.

#Diamond synthesized by chemical vapor deposition (“CVD”) has many unique and outstanding properties that make it an ideal material for a broad range of scientific and technological applications. A number of methods for diamond CVD are reported which utilize various gas mixtures and energy sources for dissociating the gas mixture. Such methods include the use of high temperature electrons in various kinds of plasma, high solid surfaces on hot filaments, and high temperature gases in combustion flames to dissociate molecules such as hydrogen, oxygen, halogen, hydrocarbon, and other carbon containing gases. Typically, a diamond crystal or film is grown on a substrate, which is usually maintained at a temperature much lower than that of electrons in the plasma, the heated surface of a hot filament, or the combustion flame. As a result, a super equilibrium of atomic hydrogen is developed near the diamond growing surface of the substrate.

#Atomic hydrogen is believed to be crucial in the diamond CVD process. It is theorized that atomic hydrogen is effective in stabilizing the diamond growing surface and promoting diamond growth at a CVD temperature and pressure that otherwise thermodynamically favor graphite growth. Consistently, the reported diamond CVD processes involve the use of hydrogen gas or hydrogen containing molecules. The most typical diamond CVD process utilizes a precursor comprising of methane gas diluted by 94-99% hydrogen. With these CVD processes, the super equilibrium of atomic hydrogen can be achieved at a varied percentage of molecular hydrogen in the gas mixture. However, these CVD processes depend on the effectiveness of the dissociation process in generating atomic hydrogen.

#Many aspects of this disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention.

#FIG. 1 is a schematic illustration of a microwave plasma enhanced chemical vapor deposition system made in accordance with the present disclosure.

#For a more complete understanding of the present disclosure, reference should be made to the following detailed description taken in connection with the accompanying FIGURE.

#The present disclosure relates to systems and methods of synthesizing diamond (e.g., crystals and/or diamond films) for a very broad range of scientific and technological applications such as optical windows, machining tools, heat spreaders, tribological coatings, sensors and actuators, electrochemical coatings, protective coatings, and wide-bandgap semiconductor devices. The systems and methods use a non-magnetic-field microwave plasma system. The systems and methods of the present disclosure use a premixed methanol-based liquid solution as the feedstock (e.g., precursor liquid). The methanol-based solution contains one or more carbon containing compounds with the molar ratio of atomic carbon to atomic oxygen being greater than one. The methanol-based solution includes methanol from about 50 to 96% by weight of the feedstock and is substantially free of water. The feedstock is introduced, in the absence of a gas stream entraining the feedstock, to a reaction chamber. Then, the feedstock is vaporized and subjected to a plasma, in the absence of a carrier gas (e.g., Argon) or a reactive gas (e.g., H2), under conditions effective to disassociate the vaporized feedstock to promote diamond growth on a substrate. The pressure range for the system can be from about 10 to 130 Torr and from about 70 to 130 Torr.

#FIG. 1 generally illustrates the plasma enhanced chemical vapor deposition system utilized in performing the methods of the present disclosure. As illustrated in FIG. 1, the precursor 5 is fed from a precursor container 6 by a conduit 7, such as a TEFLON or metal tubing, through a metering valve 8, such as a needle valve, to an inlet 3 of reactor chamber 1 in the absence of a gas stream.