Pancake Reactor

Fig. 22. Schematics of chemical vapor deposition epitaxial reactors (a) horizontal reactor, (b) vertical pedestal reactor, (c) multisubstrate rotating disk reactor, (d) barrel reactor, (e) pancake reactor, and multiple wafer-in-tube reactor (38).

Pancake Reactor The tube reactor with normal flow leads to another type of bell jar reactor referred to as the pancake reactor. It is shown in Figure 23. Here the susceptor is a disc placed horizontally and heated by induction by coils placed below it. The reactive gas flow could be introduced from above, but the favored approach is to introduce it from below at the center of the susceptor disc. Gas exhaust is at the periphery between the disc and the bell jar. 

The other configuration of silicon ept reactor that has been successful commercially is the so-called pancake reactor. The basic concept behind the system was shown in Chapter 1, Figure 22. As a production reactor, it is simple, rugged and inexpensive compared to the radiantly-heated barrel just described. The typical graphite wafer holder inside a quartz bell jar is shown in Figure 13. 

Another new epi reactor has also been introduced recently by Gemini Research. This system uses a cold quart bell jar much the same as the earlier pancake reactor. The susceptor configuration is new, however, and is shown in Figure 17,... 

In principle, the LFR is a fixed-bed reactor with a very low aspect ratio, i,e the ratio of bed height to bed diameter. Typically, the thickness of the catalyst layers is in the range of 15-75 mm. Hence, the reactor can be considered as a pancake reactor, in which the pancake has been folded for convenient accommodation in the reactor space. Because of the shallowness of the bed and its very large cross section, the pressure drop is much lower than in the case of a fixed bed of more conventional dimensions. 

Figure 1.2 Typical reactors used in chemical vapor deposition (a) pancake reactor (b) barrel reactor (c) horizontal reactor (d) low-pressure (LPCVD) reactor. (From Ref. 9.)...

Tubular Reactors. The tubular reactor is exceUent for obtaining data for fast thermal or catalytic reactions, especiaHy for gaseous feeds. With sufficient volume or catalyst, high conversions, as would take place in a large-scale unit, are obtained conversion represents the integral value of reaction over the length of the tube. Short tubes or pancake-shaped beds are used as differential reactors to obtain instantaneous reaction rates, which can be computed directly because composition changes can be treated as differential amounts. Initial reaction rates are obtained with a fresh feed. Reaction rates at... 

Modeling of Miscellaneous CVD Reactors. In addition to the classical CVD reactor configurations discussed in the preceding sections, a wide variety of CVD reactor configurations have been used, including barrel and pancake-type reactors for epitaxy and vertical cross-flow LPCVD reactors. Barrel reactors have often been modeled as horizontal reactors, because the flow geometry of one barrel side is similar to that of a horizontal reactor (Table 3 in reference 212). However, the similarity disappears if buoyancy effects and barrel rotation are included in the analysis. 

Figure 13 Vertical pancake epi silicon reactor chamber—Gemini Research.

Figure 1 illustrates conventional CVD reactors. These reactors may be classified according to the wall temperature and the deposition pressure. The horizontal, pancake, and barrel reactors are usually cold-wall reactors where the wall temperatures are considerably cooler than the deposition surfaces. This is accomplished by heating the susceptor by external rf induction coils or quartz radiant heaters. The horizontal multiple-wafer-in-tube (or boat) reactor is a hot-wall reactor in which the wall temperature is the same as that of the deposition surface. Therefore, in this type of reactor, the deposition also occurs on the reactor walls which presents a potential problem since flakes from the wall deposit cause defects in the films grown on the wafers. This is avoided in the cold-wall reactors, but the large temperature gradients in those reactors may induce convection cells with associated problems in maintaining uniform film thickness and composition. 

Oh, L Takoukis, C.G. Neudeck, G.W. Mathematical modeling of epitaxial silicon growth in pancake chemical vapor deposition reactors. J. Electrochem. Soc. 1991, B8, 554-567. 

FIGURE 28.1 Examples of CVD reactor configurations (a) pancake, (b) barrel, (c) horizontal, (d) LPCVD. 

The disassembly reactivity feedback for a spherical reactor core is derived in Appendix Al, Eq. (A1.35). However, this expression presents some problems when trying to analyze a pancaked cylindrical core, since it is not clear what the one-group buckling, j8, should be in the equivalent spherical core. This difficulty is circumvented by assuming V Fin Eq. (A1.23) is given by... 

Concerning the laboratory devices used for sonochemistry, common cleaning baths are constructed aroimd one or more ceramics fitted to the external face of a tank (p. 304). Such devices work at a single frequency, generally between 20-50 kHz, fixed by the manufacturer with an acoustic power of ca, 1 W. Immersion horns are used when more acoustic power is required. Emitters are composed of a "pancake" of PZT ceramics compressed between a titanium rod and a steel countermass (p. 305). Usually horn devices work from 20 to 100 kHz, and the acoustic power emitted can reach several tens of W. For higher frequencies, piezoceramics are simply fixed to the reactor. The reader interested in the construction of ultrasonic devices should consult Ref. 21. 

FIGURE 7.1 Schematic of a lab-scale 200 mm diameter iCVD reactor system. For a vinyl homopolymerization, a constant flow of monomer and initiator is metered into the pancake -style vacuum reaction chamber. An array of resistively heated wires, suspended a few centimeters above the substrate, heats the vapors. Laser interferometery provides real-time monitoring of the iC VD polymer thickness. The pressure of the chamber is controlled by a throttling value. Unreacted species and volatile reaction by-products are exhausted to a mechanical pump. For copolymerization, an additional monomer feed line would need to be added to the system (top image). Schematic cross-section of the iCVD reactor showing decomposition of the initiator by the heated filaments. Surface modification through polymerization of the monomer occurs on the actively cooled substrate (bottom image). 

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