Position sensing of a grating mark by heterodyne detection using a Zeeman laser

A way to detect with high resolution the position of a wafer and a mask is proposed and evaluated. In this method, a grating mark on a wafer or a mask is detected by heterodyne interference using a He-Ne Zeeman laser. Experiments show that the position of a wafer or a mask could be detected with a resolution of approximately 0.01 microm.