Microwave PECVD

Gate Oxide Tunnel Oxide f SiH4/N20 PECVD Microwave Plasma Anodisation Laser CVD... 

Figure 1.3 clearly demonstrates the luminous gas phase created under the influence of microwave energy coupled to the acetylene (gas) contained in the bottle. This luminous gas phase has been traditionally described in terms such as low-pressure plasma, low-temperature plasma, nonequilibrium plasma, glow discharge plasma, and so forth. The process that utilizes such a luminous vapor phase has been described as plasma polymerization, plasma-assisted CVD (PACVD), plasma-enhanced CVD (PECVD), plasma CVD (PCVD), and so forth. 

Tap, R. Willert-Porada, M. Synthesis of composite powders and coating of fibers by combined CVD-PECVD in a microwave heated fluidized bed reactor. In Microwave and Radio Frequency Applications, Folz, D.C., Booske, J.H., Clark, D.E., Gerling, J.F., Eds. The American Ceramic Society Westville, OH, 2003 89-97. 

Figure 5.3 (a) Schematic showing the setup of the microwave-assisted PECVD system for growing CNT, CNF, or NCD on a substrate, (b) photograph of the PECVD system, and (c) photograph of the Ar/CH Hj plasma as viewed from observation window. 

The PECVD or plasma polymerization represents a new technology that enables the production of thin films with manifold properties. Plasma polymerized layers are insoluble in organic solvents, indicative of the highly three dimensional crosslinked structure. The properties of such films can be influenced by parameters like pressure, flow rate, nature of monomer, carrier or reactive gases, power input, reactor configuration, substrate location, frequency (r.f. or microwave). In a "cold plasma" the particles are not in thermical equilibrium. The temperature of the electrons goes up to 10 °C, that of neutral particles and ions reaches about 300 C. The monomers get fragmented in the plasma and polymerize on the fibre surface. 

The catalytic chemical vapor deposition (CCVD) technique is far more developed and has great potential to be applied industrially. This technique allows for mass production at lower temperatures than the previously described methods and can be adapted for continuous production [69]. This method consists of decomposing a gas or a liquid precursor, which supplies carbon on catalytic particles (Fe, Ni, Co) in a mbe furnace at temperatures between 500 and 1,100 °C (Fig. 5.4). Besides the classic oven, heated by electric heaters, plasma furnaces (PECVD, Plasma-Enhanced Chemical Vapor Deposition) microwaves (nuCTowave, MW-PECVD), or DC (direct current, dc-PECVD) are also used. 

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