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Browse Prior Art Database

General-Purpose Self-Focussing Scanner

IP.com Disclosure Number: IPCOM000044605D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Herd, HH: AUTHOR [+3]

Abstract

This article describes a general purpose scanner which provides a capability for simultaneous focus and inspection read-out at the same point on a surface under inspection. The self-focussing feature of the scanner, here disclosed, obtains from the use of an image position change involving the vertical motion of the surface under inspection. Most substrates submitted for visual quality inspection are only approximately flat and level, thereby causing problems in maintenance of focus during scan for quality defects. Other material surfaces having specular reflective properties, such as microlithographic masks and silicon wafers, also pose significant illumination problems to a general purpose scanner used to inspect both diffuse and specular surfaces. These problems are overcome by the system shown in Fig.

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General-Purpose Self-Focussing Scanner

This article describes a general purpose scanner which provides a capability for simultaneous focus and inspection read-out at the same point on a surface under inspection. The self-focussing feature of the scanner, here disclosed, obtains from the use of an image position change involving the vertical motion of the surface under inspection. Most substrates submitted for visual quality inspection are only approximately flat and level, thereby causing problems in maintenance of focus during scan for quality defects. Other material surfaces having specular reflective properties, such as microlithographic masks and silicon wafers, also pose significant illumination problems to a general purpose scanner used to inspect both diffuse and specular surfaces. These problems are overcome by the system shown in Fig. 1, which employs an arrangement of illumination 1, and detection means 2 allowing for a simultaneous focus and read operation on the same area element of the scanned surface 3. If the angle R 4 is both the aperture half-angle and the inclination to the surface normal of the principal ray, and equality of the angles of incidence and reflection obtain, the spatial wavelength cut-off will be g/sin 2R, with a minimum occurring at R = 45 degrees. When the illumination at this angle is provided on the object plane as the image of an illuminated slit 5, re-imaged on a detector 6, departure from focus is converted to a displacement across the detector. When the detector is segmented, as in a CCD (charge-coupled device), one direction of the linear array will observe focus while the orthogonal direction will observe the data co...