Scanning system for inspecting anamolies on surfaces

Abstract

An optical scanning system and method for detecting anomalies, including pattern defects and particulate contaminants, on both patterned and unpatterned surfaces, using a light beam, scanning at a grazing angle with respect to the surfaces, a plurality of detectors and an interchannel communication scheme to compare data from each detector, which facilitates characterizing anomalies. The light beam illuminates a spot on the surface which is scanned over a short scan-line. The surface is moved in a manner so that the spot is scanned over its entire area in a serpentine fashion along adjacent striped regions. The plurality of detectors include groups of collector channels disposed circumferentially around the surface, a bright field reflectivity / autoposition channel, an alignment / registration channel and an imaging channel. The collector channels in each group are symmetrically disposed, in the azimuth, on opposite sides of the center of the scan line. The position of the collector channels, as well as the polarization of the beam, facilitates distinguishing pattern defects from particulate contaminants. The bright field reflectivity / autoposition channel is positioned to receive specularly reflected light that carries information concerning local variation in reflectivity, which is used to classify detected anomalies, as well as determine variations in the height of the surface. The alignment / registration channel is positioned to detect a maximum of the light scattered from the pattern on the surface to ensure that the streets of die present on the surface are oriented so as not to be oblique with respect to the scan line. The imaging channel combines the advantages of a scanning system and an imaging system while improving signal / background ratio of the present system.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of U.S. patent application Ser. No. 09 / 954,287, filed Sep. 11, 2001, which is a continuation of U.S. patent application Ser. No. 09 / 760,558, filed Jan. 16, 2001, now U.S. Pat. No. 6,636,302, which is a continuation of U.S. patent application Ser. No. 09 / 213,022, filed Dec. 16, 1998, now U.S. Pat. No. 6,215,551, which is a continuation of U.S. patent application Ser. No. 08 / 499,995, filed Jul. 10, 1995, now U.S. Pat. No. 5,883,710, which is a continuation-in-part application of parent application entitled “Optical Scanning System for Surface Inspection,” by Mehrdad Nikoonahad, Keith B D. Wells and Brian C. Leslie, Ser. No. 08 / 351,664, filed Dec. 8, 1994, now abandoned. This application is also related to the patent application entitled “Optical Wafer Positioning System,” by Mehrdad Nikoonahad, Philip R. Rigg, Keith B. Wells and David S. Calhoun, Ser. No. 08 / 361,131, filed Dec. 21, 1994 (“Related Applica...

AI Technical Summary

Benefits of technology

"The invention is about a method and system for detecting anamolies (small abnormalities) on the surface of a semiconductor wafer. The method involves directing a beam of light at the surface and causing relative motion between the beam and the surface so that the beam scans a path covering the entire surface. The scanning is done by reducing the size of the illuminated area (the spot size) to make it easier to detect the anamolies against a background of scattered light. By breaking up the scan path into short segments, the system can maintain uniformity of the spot along the scan line. The method and system provide a way to detect anamolies with high sensitivity while also maintaining high throughput."

Problems solved by technology

For this reason, if the anamoly is of a size which is small compared to the size of the illuminated area, the scattered light from such anamoly may be overwhelmed by and become undetectable from the background.

However, with a smaller spot size, it will be more difficult to maintain the uniformity of the spot along a long straight scan line across the entire wafer.

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