Browse Prior Art Database

2/D Area Array Solid State Feedback Automatic Wafer Alignment System

IP.com Disclosure Number: IPCOM000082961D
Original Publication Date: 1975-Mar-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 64K

Publishing Venue

IBM

Related People

Khoury, HA: AUTHOR

Abstract

Shown is an automatic wafer alignment system, which is based on the detection of the X-Y position or alignment mark within the kerf or chips of integrated circuits. The alignment mark is projected optically onto the surface of an area array solid-state feedback detector. The solid-state detector is comprised of a square matrix photodiode array.

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2/D Area Array Solid State Feedback Automatic Wafer Alignment System

Shown is an automatic wafer alignment system, which is based on the detection of the X-Y position or alignment mark within the kerf or chips of integrated circuits. The alignment mark is projected optically onto the surface of an area array solid-state feedback detector. The solid-state detector is comprised of a square matrix photodiode array.

The position of the projected alignment mark image relative to the array is determined by a two-dimension serial scan of the array. Contrast differences between the alignment mark and the background yield corresponding voltage differences at the output of the diodes. Character recognition signal processing via a computer can easily differentiate between the alignment mark and chip geometries, if any, in the proximity of the alignment mark. Further signal processing can yield the position of the alignment mark within the diode array.

Once the position of the image is known, corresponding X-Y error signals are generated which are fed to an Q-Y table in the closed-loop servo system. The servo system may be operated in either digital and/or analog modes.

As shown in Fig. 1, an illumination system 1 directs a beam of light through aperture 2. By beam splitter 3 and objective lens 4, the image of the aperture is reduced and focused on wafer 5. A filter 6 may be utilized to block light frequencies which may expose the photoresist. The reflected light from the alignment mark is collected by the objective lens 4 and focused, via beam splitter 7 and relay lens 8 on the surface of the feedback detector system 9. Thus, the projected image of the alignment mark 11 is optically relayed to the surface of the feedback detector 9.

As shown in Fig. 2, a two-dimensional 2500 photodiode area array detector 10 is provided, which consists of a 50 x 50 matrix of 0.004'' square diode elements on a center-to-center spacing of 0.004'' x 0.004''. The active individual diode area is 7.8 mils . As schematically shown in Fig. 2, the projected alignment mask is displaced by an error Ex, Ey from the ideal image location center line 12.

A computer processing system (CPS) provides a sta...