Browse Prior Art Database

Rotational Alignment of Wafers

IP.com Disclosure Number: IPCOM000040820D
Original Publication Date: 1987-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Miller, RJ: AUTHOR

Abstract

An object, such as a semiconductor wafer, having regular surface patterns that can be illuminated scatters light in a pattern of diffraction spots which can be detected to indicate rotational positioning of the wafer.

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Rotational Alignment of Wafers

An object, such as a semiconductor wafer, having regular surface patterns that can be illuminated scatters light in a pattern of diffraction spots which can be detected to indicate rotational positioning of the wafer.

In the figure, wafer 1 has a regular two dimensional pattern 2 formed on its surface at each lithographic masking step. Light from a low power helium-neon laser 3 is directed at near-gazing incidence onto the wafer surface resulting in the production of diffraction spots 4. One or more photodetector arrays 5 are provided near the wafer "horizon" to sense a corresponding spot.

As the wafer is rotated, the selected diffraction spot moves up or down in magnified motion. Spot movement near the wafer horizon has the greatest magnification and enables the most accurate wafer positioning during alignment. Placement of the detectors at a distance of 50 cm. from the point of light incidence provides several millimeters of vertical motion for one degree of rotation that can be observed with the photodetector array. Arrays positioned at opposite sides of the incident beam permit adjustment of the wafer to insure that one of the orthogonal pattern axes bisects the arrays. A helium-neon laser can be used for aligning photoresist-coated wafers since the photoresist is not sensitive to that wavelength.

Disclosed anonymously

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