Hot Wall Cross-Flow Reactor

One of the difficulties with the traditional LPCVD hot tube reactor is depletion of reactant gases as they flow down the length of the tube. To overcome this problem, designers either ramp up the temperature at the tube back end to increase deposition rates, or introduce the gases in a distributed fashion along the tube length. Neither solution is ideal, so several years ago Anicon introduced a new hot wall configuration. In this system, a hot quartz bell jar is used to provide the uniform temperature ambient for deposition. 

The reaction chamber is also quartz, and is contained within the larger bell jar. Since the reaction chamber is operated at low pressures, a ballast gas occupies the space between the bell jar and the reaction chamber. 

Reactant gases enter the reaction chamber along its vertical axis, and are introduced at the top. The wafers are placed vertically in cassettes with typical close spacing. The gas then flows parallel to the wafer surfaces and leaves the system. Therefore, the only reacting gases a wafer sees are fresh ones, and depletion is not an issue. 

Another feature of this approach is a claimed lower particulate count that the wafers are exposed to. If the longer flow path in an LPCVD furnace promotes gas phase nucleation and stirs up particles, then this system should minimize such effects. 

In the traditional LPCVD hot tube reactor, cleaning the tube required removing it from the furnace, which can be quite a job. In the Anicon system, the claim is that the quartz reaction chamber can be replaced in 15 minutes. 

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