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Coincident Illumination Optical Detector

IP.com Disclosure Number: IPCOM000039873D
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Batchelder, JS: AUTHOR

Abstract

A NxM array of light sensitive diodes or photodiodes provides a fast and efficient optical detector for a coincident detection system. When multiple sources of illumination are used in microscope versions of inspection tools, parallel images result wherein the relative intensities of said images from the different light sources are compared to detect if scattered light is present from all sources and hence indicative of particulates being present. In addition, the detector must be able to differentiate between light sources and have low noise for sensitivity. A detector array, which satisfies these criteria, is shown in the figure. It consists of a N by M (12x2) array of light-sensitive diodes or photodiodes, where N is the number of area elements that are passed to the detector and M is the number of illumination sources.

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Coincident Illumination Optical Detector

A NxM array of light sensitive diodes or photodiodes provides a fast and efficient optical detector for a coincident detection system. When multiple sources of illumination are used in microscope versions of inspection tools, parallel images result wherein the relative intensities of said images from the different light sources are compared to detect if scattered light is present from all sources and hence indicative of particulates being present. In addition, the detector must be able to differentiate between light sources and have low noise for sensitivity. A detector array, which satisfies these criteria, is shown in the figure. It consists of a N by M (12x2) array of light-sensitive diodes or photodiodes, where N is the number of area elements that are passed to the detector and M is the number of illumination sources. The operation of the detector is as follows. A reverse bias Vis applied through two series resistors R to the diode array. The signal output is coupled through capacitors C. When no light strikes the detector, only dark current is conducted across the diodes (roughly a few nanoamps per diode pair). If light from a laser arrives at the upper left diode in the array (such would typically be the case for light scattered from valid structures on the surface), that diode would conduct but essentially no current would flow from Vo to ground because the lower left diode is not illuminated by a laser. Now, howev...