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Small airborne particles within a tube, generally made of quartz, are removed by periodically passing through the tube, as indicated in Fig. 1, wafers having a high field gradient.
English (United States)
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Electrostatic Tube Cleaner
Small airborne particles within a tube, generally made of quartz, are
removed by periodically passing through the tube, as indicated in Fig. 1, wafers
having a high field gradient.
In integrated circuit semiconductor wafer processing, small quartz particles
wear off boats used for reoxidation. After several days in a reoxidation furnace,
the particles acquire sufficient static charge to be attracted to wafers being
processed in the furnace, particularly to wafers having a thin oxide.
To purge the tube of these small particles, a set of wafers, e.g., 100 wafers,
each having a high field gradient, is passed through the entire length of the tube
for about one half to one minute. Since bound surface charge attracts particles,
the set of wafers is made to have maximum oxide charge by, preferably, growing
a 500-angstrom layer of oxide on a silicon substrate having a <111>
crystallographic orientation in dry oxygen followed by a 24-hour anneal at 550
Degrees C in dry oxygen.
It has been found that the maximum field gradient occurs at the edges of
windows or openings, illustrated in Fig. 2, formed in the layer of oxide. Since the
force on the particles is proportional to field gradient, each wafer having a
diameter of 3 to 4 inches should have as many openings as possible and at least
100,000. The backside of the wafers is stripped to reduce the field in the
opposite direction when the set of wafers is placed in the boat carrying the