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Stabilizing Jets for Air Cushion Levitated Wafers

IP.com Disclosure Number: IPCOM000084361D
Original Publication Date: 1975-Oct-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 25K

Publishing Venue

IBM

Related People

Hendriks, F: AUTHOR

Abstract

Existing air-track wafer levitation employs 3 distinct rows of jets: Jo for levitation and propulsion in the z-direction, as indicated at 2, and J1 and J2 in the direction of arrows 4 and 6, respectively, for centering and levitation. The system as described thus far exhibits lateral (x-direction) instability.

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Stabilizing Jets for Air Cushion Levitated Wafers

Existing air-track wafer levitation employs 3 distinct rows of jets: Jo for levitation and propulsion in the z-direction, as indicated at 2, and J1 and J2 in the direction of arrows 4 and 6, respectively, for centering and levitation. The system as described thus far exhibits lateral (x-direction) instability.

The instability is produced by the (observed) tilt alpha of the wafer, when the wafer strays from its center line (x=0) position. More explicitly, the air-cushion pressure combined with the tilt furnishes a side force which is phase shifted with respect to the lateral (x) deviation, rendering the wafer unstable.

To remedy the instability, two extra jets J3 and J4 are directed in the directions of arrows 8 and 10, respectively, for the purpose of suppressing wafer tilt, thus eliminating air-cushion pressure and tilt induced instability.

The elimination of wafer tilt allows the centrally directed shear stresses, set up by J1, J2, J3, J4 to create a restoring force in phase with the lateral deviation
X.

The jets J3 and J4 can be fed from the same plenum pressure that serves J1 and J2.

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