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Pneumatic Orientor Adaptive Pulse Sequence

IP.com Disclosure Number: IPCOM000089507D
Original Publication Date: 1977-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Gardineer, BG: AUTHOR

Abstract

Wafer "notching" in a pneumatic orientor is greatly affected by electrostatic attraction between wafer and orientor. The mode of operation described herein minimizes these effects.

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Pneumatic Orientor Adaptive Pulse Sequence

Wafer "notching" in a pneumatic orientor is greatly affected by electrostatic attraction between wafer and orientor. The mode of operation described herein minimizes these effects.

In operation of a pneumatic orientor on air slides, a problem occurs with static attraction between the wafer and the orientor base plate. The orientor is an open-loop device that aligns the wafer about the notch by pulsing the pull-down vacuum with 50 ms pulses spaced 180 msec apart. When the pulse is off, the wafer floats up and rotates. A 50 ms vacuum pulse is sufficient to pull the wafer down and clamp it to the plate in all cases. If no static electricity is present, this rate will produce very satisfactory results, and the wafer will align in about 10 pulses.

However, some days the static charge builds up to a point where the wafer alignment would require an inordinate number of pulses, often between 50 and 100. In extreme circumstances, the wafer would never orient since the pulse gaps were not of sufficient duration to allow the wafer, under a high static attraction, to lift and rotate at all. On such occasions, an approach is to readjust the pulse gap, raising it to 220 and 250 ms length. After such adjustments, the orientor can function properly again with alignment taking place within 10 to 20 pulses.

Due to the vagaries of humidity, etc., it is sometimes necessary to readjust the pulse gap two or three times in one day to maintain the operability of the system.

In order to solve this problem, the following method is described. Operate the orientor with three different sequential pulse gaps. When alignment first starts, pulse the wafer 15 times with 180 msec. pulse gaps. Immediately following are ten 220 msec. pulse gaps, and subsequently all pulses at 250 msec. gaps. Pulses stop during the cycle at any point where the notch is sensed as being in position. This three frequency mode of operation allows successful orientation of the wafer regardless of the degree of static charge existing between the plate and the wafer. If there is no charge to sp...