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Optical Inspection Method for Masks or the Like

IP.com Disclosure Number: IPCOM000046114D
Original Publication Date: 1983-Jun-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Goodman, DS: AUTHOR [+2]

Abstract

A mask may be quickly inspected by overlaying a complementary mask and imaging a small source of light through the masks onto an observer's eye. Any light which reaches the eye is due to missing mask material.

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Optical Inspection Method for Masks or the Like

A mask may be quickly inspected by overlaying a complementary mask and imaging a small source of light through the masks onto an observer's eye. Any light which reaches the eye is due to missing mask material.

In Fig. 1, a chrome-on-glass mask 10 or the like is to be inspected for correct placement of its features and for missing chrome. It is placed in contact with a master 12 which is complementary (i.e., its opaque regions correspond to the transparent regions of a perfect mask, and vice versa). The two are aligned by means of special marks or some particular features. The pair is illuminated by a small light source 14 whose image is formed by a fairly well-corrected lens 16. The eye 18 of the inspector is placed at the source image 20. Missing chrome anywhere on the mask (such as a pinhole 22 or opening offset 23) can be seen, without moving the eye, as a light feature on a dark background. The eye is extremely sensitive when used in this way. Its sensitivity can be increased by using the apparatus in a darkened room, so that the eye becomes dark adapted. A microscope can be moved into place for more precise measurement of any defects. The system can be further enhanced by using a double source 24 (Fig.
2). One source is imaged into one eye 18 and the other source is imaged into the other eye 26, so that binocular vision is used.

This method is not limited to chrome-on-glass masks, but can be used, for example,...