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Coincident Detection Scanning Apparatus

IP.com Disclosure Number: IPCOM000039911D
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Batchelder, JS: AUTHOR

Abstract

Rough or patterned surfaces on semiconductor wafers can be inspected for particulate contamination or defects by grazing angle detection of scattered normally incident illumination. With this apparatus, a circularly polarized laser beam of small spot size, roughly 5 microns, is projected normally incident onto a wafer surface. Four detectors at incremental angles (i.e., 45o, 135o, 225o, 315o) surround the wafer and are located 0 to 5o above the wafer's surface. In operation, the laser scans and is scattered off the surface of the wafer. The detectors measure the scatter at a preset grazing angle depending on the height threshold for acceptable particulate contamination.

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Coincident Detection Scanning Apparatus

Rough or patterned surfaces on semiconductor wafers can be inspected for particulate contamination or defects by grazing angle detection of scattered normally incident illumination. With this apparatus, a circularly polarized laser beam of small spot size, roughly 5 microns, is projected normally incident onto a wafer surface. Four detectors at incremental angles (i.e., 45o, 135o, 225o, 315o) surround the wafer and are located 0 to 5o above the wafer's surface. In operation, the laser scans and is scattered off the surface of the wafer. The detectors measure the scatter at a preset grazing angle depending on the height threshold for acceptable particulate contamination. The height of the detector is determined from the fact that there is a null when the detector is placed right at the wafer's surface, and a fringe maximum at some distance above the wafer. That distance is inversely proportional to the height of the original source above the wafer's surface. Therefore, by measuring the characteristics of the grazing angle scatter, the size of the particulates can be quickly measured. This is the primary way of distinguishing between particles and pattern, as particles are higher than the pattern. Scatter from the circuit patterns is able to be distinguished from scatter from the particulate, as particulate scatter will be incident on all four detectors simultaneously while scatter from the circuit patterns is not detected as...