Browse Prior Art Database

Wafer Leveling and Height Sensing System

IP.com Disclosure Number: IPCOM000076633D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Forslund, DC: AUTHOR [+4]

Abstract

Wafer dimensional tolerances allow the working surface of the wafers to be out of parallel-with the mask working surface by as much as 0.0015''. This is corrected by holding the wafer 1 on a gimbal vacuum chuck 2 that is moved into position by three actuators 3, which are controlled by an optical sensing system.

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Wafer Leveling and Height Sensing System

Wafer dimensional tolerances allow the working surface of the wafers to be out of parallel-with the mask working surface by as much as 0.0015''. This is corrected by holding the wafer 1 on a gimbal vacuum chuck 2 that is moved into position by three actuators 3, which are controlled by an optical sensing system.

The optical sensing system consists of a light source 4, lenses 5&6 and a photoelectric quadrant detector 7. The pattern generated by reflecting collimated light onto the wafer is focused onto the surface of the quadrant detector. When equal amounts of light energy are in each quadrant, the working surface of the wafer is parallel to the surface of the quadrant detector. The quadrant detector is made parallel to the working surface of the mask by locating it, during the operation, on the same surface that establishes the bottom plane of the mask.

The pedestal itself consists of the parts shown. A vacuum is drawn between the wafer 1 and the contact plate 8. The contact plate 8 is attached to leveling plate 9 which is normally locked between the locking ball 10 and the pedestal body 11. During the leveling operation, pressure is applied beneath the locking diaphragm 12, thus lifting the locking ball 10 and releasing the leveling plate 9. After the wafer has been leveled, the pressure is removed from under the locking diaphragm 12, allowing the locking ball, to be forced downward by the locking spring 13, to prevent t...