Tilted susceptor tube reactor

Bell Jar Reactor, Barrel Susceptor If we wanted to place even more wafers in a reactor, one can go to a bell jar configuration and extend the tilted susceptor tube concept just described. Consider a reactor within a bell jar arranged as shown in Figure 21. 

Tube Reactor When initial attempts were made to extend the susceptor of Figure 17 in the flow direction, it was discovered that deposits on the last wafers were thinner than deposits on the initial ones. As discussed earlier, the explanation proposed14 was that deposition was diffusion controlled so that the thicker downstream boundary layer limited the diffusion of reactant species to the downstream wafer. An obvious solution is to tilt the susceptor up towards the rear (see Figure 8). This would have the effect of thinning the downstream boundary layer which should correct this problem. Experimental data14 have verified this effect as shown in Figure 20. 

Figure 12.5 A schematic diagram of some of the major elements of a typical low-pressure chemical vapor deposition system. Note that the entire process is typically contained within a safety enclosure because many of the reactants as process gases are either flammable or toxic. A toxic gas detector scans the interior of the enclosure, especially around the gas piping, for leaks. The scrubber reacts the source materials that are left over after passing through the reactor tube to render them harmless. Typically the valves for all sources are operated electronically so that the user does not need to open the safety enclosure except to load substrates on the susceptor. The system shown here includes a single substrate on a tilted susceptor. Batch processes are similar except in the arrangement of substrates in the reactor tube. Other reactor tube designs are also used. More specific reaction examples are given in Section 12.8.

Figure 12.9 A sketch of the use of a tilted susceptor to restrict cross sectional area of the reactor tube and hence to increase gas velocity. End view (left), side view (right). This balances or even reduces the stagnant layer thickness. The gas velocity should not increase to the point of causing turbulence in the gas.

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