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Aligning a Mask Above a Wafer During the Manufacture of Integrated Circuits

IP.com Disclosure Number: IPCOM000083915D
Original Publication Date: 1975-Aug-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Korth, HE: AUTHOR

Abstract

Wafer edge E1 or E2 serves as an aligning mark. Light L impinging upon the wafer edge is scattered or reflected asymmetrically and perpendicularly to the edge. For a particular solid angle, the reflected light for the two wafer edges E1 and E2 is separately detected by photodiodes 1 and 2. When the two photodiode signals are equal, which is achieved by laterally shifting the mask above the wafer, the required degree of alignment has been reached.

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Aligning a Mask Above a Wafer During the Manufacture of Integrated Circuits

Wafer edge E1 or E2 serves as an aligning mark. Light L impinging upon the wafer edge is scattered or reflected asymmetrically and perpendicularly to the edge. For a particular solid angle, the reflected light for the two wafer edges E1 and E2 is separately detected by photodiodes 1 and 2. When the two photodiode signals are equal, which is achieved by laterally shifting the mask above the wafer, the required degree of alignment has been reached.

In an arrangement for implementing this method, the mask is optically imaged onto the tiltable wafer which is movable in both coordinate directions. The light scattered or reflected by the wafer edges is fed, via a beam splitter, to a field mask apertured in places to pass the reflected light to be evaluated.

The light permeating the apertures is transferred to one pair of photodiodes for each coordinate direction and direction of tilt. Each pair of photodiodes is connected to a differential amplifier whose output signal is used to control the wafer.

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