Tre Semiconductor Equipment Corporation

Lawrence S Green

Boris Meshman

Thomas A Kerekes

David Karlinsky

A step-and-repeat exposure system incorporates a method for achieving die-by-die alignment at high speed in order to increase the throughput of the system. In order to align circuit patterns which are to be exposed onto a semiconductor wafer in an overlapping fashion, the wafer is initially moved to a target position in order to view an alignment target previously formed on the wafer, and is subsequently moved to an exposure position. The movement to the exposure position is controlled as a function of the calculated position of the alignment target. The method involves initiating the video scan to view the alignment target prior to the stage coming to a complete rest at the target position. The characteristics of the stage motion are determined and the acquisition of the video data is initiated as soon as the oscillation of the stage has subsided by an acceptable amount. By initiating the video scan at an early point, a significant decrease in the alignment time at each die site is achieved.

High speed alignment method for wafer stepper

This automatic wafer alignment technique may be used in a step-and-repeat photomicrolithographic exposure system accurately to prealign a wafer before exposure to the B-level and subsequent reticles, and automatically to align the wafer at each die site prior to exposure. A search technique optimizes location of the global targets used for wafer prealignment. The search begins at the most likely target position and proceeds through a search area established by the maximum expected rough prealignment error. A wafer alignment target configuration consisting of a cross with one elongated arm and a short crossbar is used to optimize target verification. To locate targets a video image is digitized and the average intensity at each video scan line and column is obtained and stored. This data is used to determine the presence in the video image of feature edges. A table of all such edges is established. These listed edges are correlated to determine all pairs of edges that may represent potential targets. From these, the best target is selected by comparing certain weighted parameters of each potential target.

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Los Angeles, CA, United States of America

Lawrence S Green