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David Crowley, Tokyo Electron Texas, Inc., Austin, TX
Flow characteristics within the exhaust cup
Tokyo Electron Texas, Inc., (TEX) is part of a worldwide organization,
Tokyo Electron Limited (TEL), a leader in semiconductor and LCD production
equipment based in Japan. TEX performs research and development for Tokyo
Electron’s Clean Track systems, which dominate the market because
of their reputation for superior reliability and performance.
Clean Track systems are used in the photolithography process that silicon
wafers undergo during microchip fabrication. They are used to coat silicon
wafers with a sub-micron thick layer of photo-sensitive polymer (called
photo-resist), perform baking and surface preparation processes, send
the wafers to a pattern exposure tool, and develop the photo-resist after
exposure. The precision of the resulting pattern is strongly dependent
on the uniformity of the photo-resist thickness across the wafer. This
thickness is governed by the wafer rotation speed and air flow inside
the system, which is driven in part by the design of an exhaust cup, used
to remove volatiles. To understand the features of two different exhaust
cup designs, two models of about 1.4 million cells each were analyzed
using FLUENT.
The FLUENT results were in agreement with a simulation done previously
by TEX’s parent company, Tokyo Electron Kyushu (TKL), which used
slightly different boundary conditions and other software tools. The
results supported observations of vortices created at high spin speeds,
giving engineers confidence in the simulation techniques and providing
valuable information related to the modification of the exhaust cup to
improve the system performance. In the future, FLUENT will be used to
verify improvements to the airflow and exhaust system designs.
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