Method and apparatus for overlay measurement

摘要

A process for measuring the alignment of different layers on a semiconductor wafer (33) includes forming repetitive alignment marks (14, 24) having substantially the same period on the different layers on the wafer (33). The images of the overlay alignment marks (14, 24) are converted from space domain to frequency domain through Fourier transformations. The alignment measurements are performed by calculating the phase difference between the images corresponding to the repetitive patterns (14, 24) on different layers. <IMAGE>