Microwave CVD

The hydrogen required for the deposition of a diamond film can furthermore be generated in the plasma arising from microwave irradiation at a frequency of 

Method Temperature (°q Pressure (Torr) (psi) Growth rate (pmh ) 

Still the inhomogeneity of the plasma has adverse effects on the outcome of MW-CVD. It causes an uneven decomposition of the hydrocarbon and an inhomogeneous distribution of the reactants in the gas phase. At the worst this will lead to an uneven deposition of the diamond film on the substrate with both the thickness and the quality of the film potentially being affected. 

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Another approach is to coat the cutting tool material with a carbide former, such as titanium or siUcon or their respective carbides by CVD and deposit diamond on top of it. The carbide layer may serve as an iaterface between diamond and the cemented carbide, thus promoting good bonding. Yet another method to obtain adherent diamond coatings is laser-iaduced microwave CVD. By ablating the surface of the substrate with a laser (typically, ArF excimer laser) and coating this surface with diamond by microwave CVD, it is possible to improve the adhesion between the tool and the substrate. Partial success has been achieved ia this direction by many of these techniques. 

Fig. 3 (a) Initial and (b) intermediate growth morphologies of microwave CVD diamond films. 

Fig. 4 Schematic layout of a modified microwave CVD reactor for nanocrystalline diamond deposition.

Microwave CVD uses microwave energies ranging from several hundreds of watts to tens of kilowatts at a frequency of 915 MHz or 2.45 GHz to dissociate active species. The most common MWCVD systems use 2.45 GHz. 

Gruen and co-workers first succeeded in the respective preparation by modifying a typical microwave CVD method (Figure 6.20). In addition to the carbon source... 

In microwave-CVD (MWCVD) the plasma is generated by microwave irradiation. 

Erickson et al. (1996) have measured the CH3 column density for a microwave CVD reactor with a feed gas of CH4 diluted in H2. A schematic diagram of their apparatus is shown in Fig. 7. The temperature of the discharge was determined to... 

Fig. 8. CH3 density versus input CH4 mole ftaction in a microwave CVD reactor. (Reprinted with permission from Erickson et al., 1996, Plasma Sources Sci. Technol., 5, 761, 1996 lOP Publishing, Ltd.)...

Erickson et al. (1996) tried to detect CH absorption in a microwave CVD reactor using CH4 diluted in H2 as the feed gas. They were unable to detect the CH absorption. Using the detection limit of their system, they placed an upper limit of 10 cm on the CH density. From this and their measured CH3 density, they placed an upper bound on the hydrogen dissociation ratio [H]/[H2] of 0.008. 

The high-sensitivity white-light absorption spectroscopy of hydrogen-deficient microwave CVD used for nanocrystalline diamond growth done by Goyette et al. (1998a) used the (0,0) vibrational band of the cPYl — a II electronic transition of C2, known as the Swan system. Figure 20 shows a typical absorption spectrum from this band. The bandhead for the (0,0) Swan band is located at 516.5 nm. The... 

Zhang et al. [194] at Harvard were able to synthesize an amorphous CN thin film with composition C2N. This material had exceptional hardness [195-197]. In some cases, tiny crystallises of covalent C-N were observed in the amorphous films [196-202]. Bhusari et al. in February 1997 [193] were able to synthesise large crystals (750 tm) of Si-containing carbon nitride consisting of a predominantly C-N network, by microwave CVD. 

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