Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Linear Photodiode Feedback Automatic Alignment System

IP.com Disclosure Number: IPCOM000082960D
Original Publication Date: 1975-Mar-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 63K

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 of an alignment mask in the kerf of large-scale integrated circuit chips on a wafer or on special alignment sites. The image of the alignment mark, consisting of a cross, is projected optically onto the surface of a linear array of photodiodes.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

Linear Photodiode Feedback Automatic Alignment System

Shown is an automatic wafer alignment system, which is based on the detection of the X-Y position of an alignment mask in the kerf of large-scale integrated circuit chips on a wafer or on special alignment sites. The image of the alignment mark, consisting of a cross, is projected optically onto the surface of a linear array of photodiodes.

The position error of the image relative to the linear array is determined by scanning the array, and determining the location of each leg of the cross within the array. Location of the image is determined by contrast differences between the alignment mark and its background, which cause corresponding voltage differences at the output of the diodes. Data acquisition and reduction is performed via a computer.

Once the position of the image is known, corresponding X-Y error signals are generated which are fed to an X-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 is optically relayed to the surface of the feedback detector 9.

As shown in Fig. 2, a linear array of 256 photodiodes 10 is provided consisting of 0.001 inch square diode elements on a center-to-center spacing of
0.001 inch. Initially, the diode array is vertic...