Status and Applications of Diamond and Diamond-Like Materials An Emerging Technology (1990) / Chapter Skim
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2 Growth Processes
2 Growth Processes
Pages 19-60
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From page 19... ...
Over the past 10 years workers have moved from a generally held belief that no practical process for low-pressure diamond growth was possible to the current realization that nearly any method that produces a ready supply of atomic hydrogen and some carbon-containing species works. Furthermore, the crystal quality and related morphology are remarkably similar for all the various processes and their variants, even though they range from plasma-enhanced processes to heated-filament-assisted nonplasma processes.
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From page 20... ...
A relatively unexplored area of deposition Space" is the use of both bombardment and chemical vapor deposition processes simultaneously at temperatures not exceeding 300 to 500.C. Such materials may have properties intermediate between the diamond and DLC and DEHC materials.
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From page 21... ...
As mentioned earlier, it now seems that just about any process that efficiently produces atomic hydrogen and carbon-containing species can yield diamond films over some range of conditions. In some deposition processes both physical and chemical processes take place simultaneously, but such distinctions will not be made specifically.
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From page 22... ...
at pressures where diamond is a stable phase in equilibrium with a metal-rich liquid. In this system there exists a eutectic at lower P-T conditions than required for direct conversion.
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There are many cell designs to cover the needed variations, but common to all is internal heating by passing a low-voltage high current through the cell. Direct heating usually means the current passes directly through the reactants (e.g., a mixture of iron and graphite for diamond synthesis)
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Control of Crystal Size The static process permits control of grain size simply by controlling the time the system remains at the desirer! P-T conditions.
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at higher temperatures, near the diamond-graphite equilibrium curve. (This is opposite to the morphology changes in CVD diamond growth.)
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Type IIA diamond is essentially pure carbon and exhibits the highest thermal conductivity. Type lIB is the p-doped semiconducting diamond with boron in lattice sites.
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Most natural diamonds (IA) are two-phase mixtures of platelets precipitated in the host diamond.
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From page 28... ...
There is room for improvement in the bonding of CVD diamond to any material. CHEMICAL VAPOR DEPOSITION PROCESSES It was the recognition of the role of atomic hydrogen in the vapor deposition approach that led Russian workers to the first successful growth of diamond films at commercially practical deposition rates (>1 '~m/hr)
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The most extensively studied process is microwave plasma-enhanced chemical vapor deposition (MPECVD)
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1987. Growth of diamond thin films by dc plasma chemical vapor deposition.
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FIGURE 2-5 Schematic diagrams of various plasma-enhanced CVD techniques for diamond growth: (a) microwave PECVD (Kamo et al., 1983~; (b)
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From page 32... ...
and conceptually. The optimum conditions for diamond growth involve, among other factors, a substrate temperature of about 1000oC and a high percentage of atomic hydrogen.
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From page 33... ...
TABLE 2-2 Nonplasma Deposition Processes for Diamond Film Growth Deposition Rate Techniques (,~m/hr) References Heated-Filament CVD 0.1-20 1,2 - wound filament - small-bore tube - substrate biasing Laser-enhanced CVD 3 Kerr to References: 1.
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From page 34... ...
have been used to "seed" the surface (Bachmann et al., 1988~. Substrate Temperature For the diamond films with the highest level of crystal perfection, the substrate temperature is usually in the range of 900 to 1000.C.
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and crystal size and perfection (at about 0.2 to 0.5 percent CHIP. Recently diamond films of apparent comparable quality have been grown from CO.
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From page 36... ...
Fundamental Issues in CVD Processes There have been few reported studies that directly address the fundamental issues of nucleation and growth of vapor-deposited diamond films and the resulting film's structural and chemical defects. This section, therefore, deals more with speculations and attempts to identify critical areas of research.
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, and others have reviewed the chemical kinetics model for diamond vapor deposition developed by Derjaguin and Fedoseev (1977) and Fedoseev and coworkers (1984~.
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From page 38... ...
that requires a critical temperature was suggested. Clearly, else nucleation stage in diamond growth poses the most important questions that will have to be answered before there is significant progress in solving practical problems of lowdefect-density polycrystalline films, high purity, homoepitaxy, heteroepitaxy, and controlled morphology.
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From page 39... ...
et al., 1988) measurements of gas-phase species during enhanced CVD diamond growth have shown that both CH3 and C2H2 species are present in sufficient quantities to account for diamond growth.
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Atomic hydrogen, which is a necessary ingredient in diamond film deposition, is a highly reactive element. Since silicon substrates and fused silica reactor tubes and bell jars are often used, silicon is a common impurity.
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From page 41... ...
An evolutionary growth model for diamond films is expected to be important as attempts are made to design and engineer films for specific applications. A complete description and understanding will entail a number of the fundamental issues already discussed -- nucleation intermediate layers, renucleation, intergrowth of crystals, evolutionary selection, and effects of
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From page 42... ...
Growth cones are a very common feature of many different types of deposition processes and, in fact, are a common occurrence in deposition of some of the materials discussed in this report, e.g., SiC. Growth cones commonly affect a variety of properties, usually in a negative fashion.
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From page 43... ...
Thus these materials can be grown on relatively low-temperature substrates. In the case of diamond-like carbon films, the coatings have been reported to possess high electrical resistivity, high hardness, low coefficient of friction, and a relatively high transparency in the infrared.
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Pulsed discharge rail gun with auxiliary ion beam FIGURE 2-11 Processes for growing carbon films from hydrocarbon gases (Angus et al., 1986~.
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2 x 10 5 100 eV Dual ion beam deposition 75 CH4 (Ar) 5 x 10 90- 250 eV Single beam direct deposit, on 76
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1980a. Electrical and optical properties of hydrogenated amorphous carbon films.
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1979. Properties and coating rates of diamond-like carbon films produced by FR glow discharge of hydrocarbon gases.
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1986. Thin film growth rate ejects for primary ion beam deposited diamondlike carbon films.
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Equipment has been constructed for coating objects up to 1 m in diameter. Figure 2-15 shows the original sacrificial cathode ion source developed for direct ion beam deposition of diamond-like carbon coatings.
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field Teflon tube FIGURE 2-15 Direct ion beam deposition from solid precursor configuration.
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A second ion source, operated at a lower ion energy, can be employed to further bombard the sample surface. This results again in films with improved mechanical and optical properties.
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From page 52... ...
._. I ~ Cathode Neutralizer Diamond- Like Film l l Beam Mixture of Methane and Ardors FIGURE 2-17 Dual ion beam deposition configuration (Mirtich, 1981~.
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From page 53... ...
Direct ion beam deposition techniques, on the other hand, utilize pressures in the submillitorr region. Because of this fundamental difference, coatings produced by ion plating typically grow at faster rates but have poorer optical and electronic properties than those produced by ion beam processes.
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From page 54... ...
Size of Substrates Process equipment for coating substrates up to 1 m in diameter has been constructed for ion plating and related deposition systems. Until recently, the area coated by direct ion beam processes has been restricted by the unavailability of large-area ion beam source technology.
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Microstructure Diamond-like carbon films have been shown to contain a variety of hydrogen contents and range of atomic structures. The majority of the dense films have been found by x-ray examination to be amorphous.
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From page 56... ...
The ,B-phase has been produced by vapor deposition processes, and various procedures have been developed for heteroepitaxial growth on large-area silicone substrates based on various buffer layers to satisfy the mismatch in lattice parameter and thermal expansion coefficient. Thick layers have been successfully prepared by a number of workers (e.g., Nishino et al., 1980; Liaw and Davis, 1985~.
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From page 57... ...
1988. Measurement of stable species present during filament-assiste~i diamond growth.
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1987. Growth of diamond thin films by dc plasma chemical vapor deposition.
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From page 59... ...
1985. Preparation, Structure and Properties of Hard Coatings, in Thin films from Free Atoms and Particles.
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