Advanced Semiconductor Laboratory
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Showerhead design for MOCVD


By
Kuang-Hui Li

December 26, 2016 - Posted in Discussion
​For MOCVD deposition, precursors will thermally decompose, then diffuse onto the substrate. However, there is an unfavorable process called parasitic reaction if a chemical reaction happens within precursors. The parasitic reaction will cause several problems. First, precursors will form an abduct or complex which these abduct or complex will not be deposited on the substrate, and it reduces the growth efficiency since some of the precursors are very expensive. Second, the parasitic reaction will generate particles and fall on the substrate. These particles can be considered as small crystal with different lattice orientation, and these particles will reduce the quality of a single-crystal thin film. The purpose of the showerhead is to prevent precursors from the parasitic reaction before precursors thermally decompose and diffuse onto the substrate.
KH 1.JPG 
Figure 1, Thomas Swan Showerhead.
 
The most common showerhead design is Thomas Swan showerhead, as shown in Fig. 1, and it has three layers. From the bottom to the top are layers of cooling water, layers for precursor 1, and layers for precursor 2, respectively. However, this design has a drawback which it has too many welding points. If some welding points are not sealed or deteriorate, the reactor will face water leaking issue, if the leaking point is small. If the leaking point is large, a few water droplet drop on a hot substrate will cause severe damage to the reactor. Axitron (acquire Thomas Swan in 1999) improves welding skill, but water leaking issue is a major drawback.
 
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