Target acquisition technique for CD measurement machine
AssigneeApplied Materials, Inc.
InventorsBo Su, Mircea Dusa
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Abstract
In a process for measuring the CD of a mask pattern transferred to a semiconductor wafer, in which a series of dies are sequentially inspected by first locating a target area on the die and then vectoring to a CD measurement area, a technique is used whereby the stored image of an alignment target is used for pattern recognition in the process of acquiring each subsequent die's target. The stored image is updated with each new die inspected, using an image of the most recently acquired target area. In this manner, the stored target image always closely approximates the next target to be acquired. Thus, according to the invention, difficulties in recognizing and centering on the target are minimized, and CD measurements of much higher reliability can be effected.
Claims12
A method of improving the reliability of a critical dimension (CD) measurement in a photolithographic process, comprising the steps of:
- a. storing as a reference an image of a selected target formed on a photolithographically exposed semiconductor wafer, and storing a vector value between a point of said selected target and a CD measurement site;
- b. performing a pattern recognition process using said reference image, to acquire a next target formed on another region of said wafer, and using said vector value to acquire a CD measurement site within said another region;
- c. updating said reference image by replacing said stored image with an image of said next target;
- and
- d. repeating step (b) using the updated reference image.
A method of improving the reliability of an optical measurement, comprising the steps of:
- storing as a reference an image of a first target area formed on a device, and a vector value between a point of said first target area and a measurement site;
- performing a pattern recognition process using said reference image, to acquire a second target area formed on a second region of said device, and using said vector value to acquire a measurement site within said second region;
- updating said reference image by replacing said stored image with an image of said second target area, performing a pattern recognition process using said update reference image, to acquire a third target area formed on a third region of said device, and using said vector value to acquire a measurement site within said third region.
A method of improving the reliability of site location, comprising the steps of:
- a. storing as a reference an image of a selected target;
- b. performing a pattern recognition process using said reference image, to acquire a next target;
- c. updating said reference image by replacing said stored image with an image of said next target;
- and
- repeating step b using said updated reference image, obtaining a simulated image of said next target using a simulator operating on an original target;
- and,
- using said simulated image to confirm correct acquisition of next target.
Dependencies are inferred from the claim text.