TARGET ACQUISITION TECHNIQUE FOR CD MEASUREMENT MACHINE

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.