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Optical Inspection System

IP.com Disclosure Number: IPCOM000042530D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Tsukamoto, K: AUTHOR

Abstract

The system serves to automatically detect defects on a photomask, a printed-circuit board or the like which has printed patterns thereon. In this system, the defects on the printed patterns are detected by the fact that the printed patterns have regular outlines and the defects have irregular outlines. This system has two or three linear image sensor arrays which scan the patterns. A logical exclusive OR of the outputs of two of the arrays is taken. The signal widths of the exclusive OR represent the edges of the patterns and of the defects. The signal widths of the exclusive OR caused by the patterns have predetermined values. On the contrary, the signal widths of the exclusive OR caused by the defects are not equal to the predetermined values.

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Optical Inspection System

The system serves to automatically detect defects on a photomask, a printed- circuit board or the like which has printed patterns thereon. In this system, the defects on the printed patterns are detected by the fact that the printed patterns have regular outlines and the defects have irregular outlines. This system has two or three linear image sensor arrays which scan the patterns. A logical exclusive OR of the outputs of two of the arrays is taken. The signal widths of the exclusive OR represent the edges of the patterns and of the defects. The signal widths of the exclusive OR caused by the patterns have predetermined values. On the contrary, the signal widths of the exclusive OR caused by the defects are not equal to the predetermined values. Therefore, the defects are able to be distinguished by measuring the signal widths of the exclusive OR of the outputs of two arrays. As shown in Fig. 1, the system has a light source 10, a transparent patterned object 11, an optical lens means 12, one or more linear image sensor arrays 13, such as CCD or MOS, an X-Y table 14, and a data processor 15. In this case, the system has three linear image sensor arrays 1, 2 and 3, each having 4049 cells in its lengthwise direction of 20 mm, which are arranged in parallel, apart from each other with the same space of 40 mm, as shown in Fig. 2, and moved by the X-Y table 14 in their lengthwise and transverse directions. The system can detect defects which are larger than 40 mm. The patterned object 11 is, for instance, a glass master provided with printed patterns thereon which are defined by only linear and circular outlines, as shown in Figs. 3, 4 and
5. The linear outlines in Fig. 3 make angles of 0OE, 45OE, 90OE and 135OE with each other. The linear outlines may make other predetermined angles.

The glass master 11 is positioned at a predetermined angle with respect to arrays 1, 2 and 3. Referring now to Fig. 3, two of the arrays, for example, arrays 1 and 2, scan the linear patterns simultaneously in their lengthwise directions D1 and D2. Then, the outputs of arrays 1 and 2 are taken by the logical exclusive OR. All of the logical exclusive ORs can be classified into one of three signal types, where a first type S0 has a signal width of substantially zero length caused by a perpendicular pattern P1, a second type S1 has a signal width of a predetermined constant length caused by a slant pattern P2, and a third type S2 has a signal width of very long length caused by a horizontal pattern P3, unless there is no defect on the patterns. If there are any defects on the patterns, the logical exclusive ORs SD do not belong to any of above-mentioned three types S0, S1 and S2 since they have signal widths different from S0, S1 and S2. Since the signal widths of the exclusive ORs SD caused by defects D are between S0 and S1 or between S1 and S2, any defects can be detected by measuring signal widths of the exclusive ORs. When th...