Method for overlay measurement in exposure process

Abstract

A method for overlay measurement in an exposure process uses a multiplex filter having a plurality of filters. A first filter is selected from the plurality of filters and positioned underneath a lens of an overlay measurement apparatus. Next, a determination is made whether overlay marks formed on a wafer are perceptible through the lens and the first filter. If perceptible, the overlay marks are measured. If the overlay marks are not perceptible, the first filter is replaced with a second filter from the plurality of filters, and a determination is made whether the overlay marks are perceptible through the second filter and, if perceptible, the overlay marks are measured. Accordingly, there is no need to stop the exposure process if there is a failure to perceive the overlay marks. Further, the method, according to an embodiment of the present invention, increases the efficiency of the exposure process, especially, the wafer alignment process.

Dependencies are inferred from the claim text.