Glow discharge configurations

Plasma polymerization is usually carried out in a low pressure glow discharge sustained by either a dc or an ac electric field. Examples of the reactors used for this purpose are shown in Fig. 1. The simplest configuration involves a pair of circular parallel plate electrodes mounted inside a glass bell jar. The lower electrode usually serves as the substrate holder and is sometimes heated or cooled. Monomer is introduced through a feed tube and unconsumed monomer and gaseous products are withdrawn through a port in the base plate. 

In addition to thermally-created CVD films, much work has been done using glow discharges to modify the deposition. Therefore, Chapter 2 reviews the fundamentals of plasma-enhanced CVD (PECVD). Initially, the basic character of a plasma is covered. Then we discuss the influence of the reactor configuration on the plasma behavior and PECVD deposition. The two major PECVD reactor systems are reviewed, and then several new concepts are considered. 

Figure 13.1 Schematic diagrams of the two configurations of the electrode setup used in the glow discharge polymerization process, (a) A1 substrate was used as powered electrode and (b) A1 substrate was floating in between the two parallel electrodes.

The primary glow discharge reactor in this configuration could be used for plasma coating in a low-pressure regime, in principle however, in consideration of flow pattern in such a multiple shelves reactor and electrical field in multiple electrodes, it is difficult to achieve uniform coatings in such a mode of operation. 

The distribution of polymer deposition observed in the plasma polymerization of acetylene at different flow rates (and different system pressures under plasma conditions) is shown in Figure 20.2. It should be noted that acetylene is the fastest polymerizing hydrocarbon and the system pressure decreases on the inception of glow discharge. In this particular configuration of reactor, the monomer does not pass the radio frequency coil, and presents a typical case in which the creation of chemically reactive species occurs at the boundary where the monomer meets the luminous gas phase, i.e., activation by luminous gas, not by ionization. 

Fig. 8.13. Simplified representation of five common source configurations for glow-discharge. (Reproduced with permission of the American Chemical Society.)...

Fig. 72. Restrictor tube configurations and current-voltage characteristics of flat cathode dc glow discharges. (A) According to Grimm (B) floating restrictor (C) restrictor made of...

Figure 4-19. Hollow-cathode configuration of glow discharges.

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