Plasma reactor

In practical applications, gas-surface etching reactions are carried out in plasma reactors over the approximate pressure range 10 -1 Torr, and deposition reactions are carried out by molecular beam epitaxy (MBE) in ultrahigh vacuum (UHV below 10 Torr) or by chemical vapour deposition (CVD) in the approximate range 10 -10 Torr. These applied processes can be quite complex, and key individual reaction rate constants are needed as input for modelling and simulation studies—and ultimately for optimization—of the overall processes. 

Electron Cyclotron Resonance (ECR). A microwave plasma can also be produced by electron cyclotron resonance (ECR) (see Ch. 5, Sec. 9). An ECR-plasma reactor suitable for the deposition of diamond is shown schematically in Fig. 5.19 of Ch. 5.[ °]... 

Hussain, T., and Ibberson, V., Synthesis of Ultrafme Silicon Nitride in an RF Plasma Reactor, in Advances in Low-Temperature Plasma Chemistry, Technology, Applications, 2 71-77, (H. Boenig, ed), Technomic, Lancaster (1984)... 

A thermal plasma system has been developed for the decomposition of methane. A schematic diagram of the experimental apparatus is shown in Fig. 1. The system consists primarily of D.C. plasma torch, plasma reactor and filter assembly. Plasma was discharged between a tungsten cathode and a copper anode using N2 gas. All the experiments were carried out at atmospheric pressure at 6 kW input electric power and N2 flow rate of 10 to 12 1/min. The feed gas (CH4) flow rates were varied from 3 to 15 1/min depending on the operating conditions, shown in Table. 1. 

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.

The scale-up from a small to a large plasma reactor system requires only linear extrapolations of power and gas flow rates. However, in practice, the change in reactor geometry may result in effects on plasma chemistry or physics that were unexpected, due to a lack of precise knowledge of the process. Fine tuning, or even coarse readjustment, is needed, and is mostly done empirically. 

FIG. 5. Schematic representation of the ASTER deposition system. Indicated are (I) load lock. (2) plasma reactor for intrinsic layers. (3) plasma reactor for />-type layers. (4) plasma reactor for t -type layers, (5) metal-evaporation chamber (see text). (6) central transport chamber. (7) robot arm. (8) reaction chamber, (9) gate valve, (10) gas supply. (11) bypass. (12) measuring devices, and (13) tur-bomolecular pump. 

In the plasma reactor dedicated for intrinsic material deposition (2 in Fig. 5), only hydrogen and silane are used, along with argon. A mixture of trimethylboron (5% TMB in H2), SiHa, and methane (CH4) is used in the / -plasma reactor (3 in Fig. 5). Diborane can also be used. A mixture of phosphine [PH3 (1% in H2)] and SIH4 is used in an n-plasma reactor (4 in Fig. 5). All gases are of 6.0 quality (99.9999% pure) if available from manufacturers, and otherwise as pure as possible. 

FIG. 35. Vertical cross section of the reaction chamber equipped with the mass spectrometer system. Indicated are QMF. the quadmpole mass filter ESA. the electrostatic analyzer CD, the channeltron detector DE, the detector electronics DT, the drift tube lO, the ion optics TMP, the turbomolecular pump PR, the plasma reactor and MN. the matching network. 

By coupling a non-thermal plasma reactor to a catalytic reactor containing alumina alone, Baudin [32] have observed the DeNO function of alumina at low temperature,... 

Figure 5.14. Detection of organic products oxygenates and organic nitrogen-containing compounds at the outlet of non-thermal plasma reactor without catalyst. Feed NO (500 ppm) - C3H6 (2000ppm Cj) - 02 (8 vol.%) - N2 [32],...

It is clearly shown, as already found by Penetrante and co-workers [33], Hoard and Balmer [34] and Dorai and Kushner [35], that the plasma reactor is able to produce oxygenates and RNO from RT to 400°C (673 K). Those species correspond to function 2 and they are necessary for the DeNO reaction according to the present model. 

Experiments in real diesel exhaust gas have been carried out as well [101] using a pulsed DBD and V205/Ti02 catalysts placed downstream of the plasma reactor. NO removal reached 90% under no-load conditions, for catalyst temperatures above 373 K... 

Ogata, A., Mizuno, K., Kushiyama, S. and Yamamoto, T. (1998) Methane Decomposition in a Barium Titanate Packed-Bed Nonthermal Plasma Reactor, Plasma Chem. Plasma Process 18, 363-73. 

Takaki, K., Shimizu, M., Mukaigawa, S. et al. (2004) Effect of Electrode Shape in Dielectric Barrier Discharge Plasma Reactor for NOx Removal, IEEE Trans. PI. Sci. 32, 32-8. 

Li J, Sato M, Ohshima T (2007) Degradation of phenol in water using a gas-liquid phase pulsed discharge plasma reactor. Thin Solid Films 515 4283-4288... 

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