Microwave Plasma CVD Reactors

There are various types of CVD reactors for diamond film synthesis, and they are presented in this chapter. A recent advent of production-type CVD reactors is revolutionary changing diamond film from research to production phase. In reading the articles of CVD diamond, it shonld be noted that in some reactors, the substrate temperature cannot be controlled independently of other parameters. The gas presssure P, the microwave power Pj and other parameters influence Ts, and thus the plasma condition is concurrently changed. Therefore, a meticulous care is necessary to see whether the results intrinsically arise from T, or from the plasma condition due to the change in other parameters, when one interprets experimental data. 

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Microwave Plasma CVD reactors use very similar conditions to hot filament reactors, and despite being significantly more expensive, are now among the most widely used techniques for diamond growth. In these... 

A.7.1. Microwave plasma CVD reactors A.7.2. Hot filament CVD reactor A.7.3. DC plasma CVD reactor A.8. Crystal growth modes A.9. Carbon materials A. 10. Miscellaneous notations... 

NIRIM-type A microwave plasma CVD reactor developed by National Institute for Research in Inorganic Materials (NIRIM), Japan. This laboratory is now called National Institute for Materials Science (NIMS). 

Figure 5.4 Block diagram of a typical microwave plasma CVD reactor.

There are several types of microwave plasma CVD (MPCVD) reactors designed by several organizations. The widely known reactors are presented in Section 3 ... 

In the laboratory, researchers can obtain diamond electrodes from three different sources (i) from their own home-built systems, typically HF-CVD (ii) from commercial growth systems, for example, MW plasma CVD reactors from Seki Diamond Systems, Microwave Enterprises, Diamond Materials, and iPlas Cyran-nus and (ill) purchase the diamond electrodes from a commercial source, as listed in Table 5.2. 

Figure 5.2. Two of the more common types of low pressure CVD reactor, (a) Hot Filament Reactor - these utilise a continually pumped vacuum chamber, while process gases are metered in at carefully controlled rates (typically a total flow rate of a few hundred cubic centimetres per minute). Throttle valves maintain the pressure in the chamber at typically 20-30 torr, while a heater is used to bring the substrate up to a temperature of 700-900°C. The substrate to be coated - e.g. a piece of silicon or molybdenum - sits on the heater, a few millimetres beneath a tungsten filament, which is electrically heated to temperatures in excess of 2200 °C. (b) Microwave Plasma Reactor - in these systems, microwave power is coupled into the process gases via an antenna pointing into the chamber. The size of the chamber is altered by a sliding barrier to achieve maximum microwave power transfer, which results in a ball of hot, ionised gas (a plasma ball) sitting on top of the heated substrate, onto which the diamond film is deposited.

From the microwave supported plasma CVD, which is also used to deposit diamond films (Section 6.3.1), a method generating nanodiamond in a flow reactor is derived. The sole modification to obtain single particles is to omit the substrate from the reactor so the diamond particles formed are carried along by the gas current to precipitate only in cooler parts of the apparatus placed downstream after the oven. As carbon source, dichloromethane in a mixture with oxygen is employed. The main product obtained with this method is amorphous, graphitic material. This may, however, quantitatively be removed by a treatment with 70% perchloric... 

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.)...

Figure 8.31. Three reactors for plasma-CVD (a) dc-reactor (b) rf-reactor (c) microwave reactor.

Figure 2.1 shows a schematic diagram of the CVD equipment. A commercial low-pressure microwave (2.45 GHz) plasma reactor, Model AX5400 (ASTeX Coip., Wohurn, MA) was used (Fig. 2.2). This unit consists of a vacuum system, a microwave generating system and a gas supply system.

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