| 摘要 |
PURPOSE:To enhance the utilization efficiency or S/N ratio of illumination beam by markedly reducing the reflected light returning to a light source, by providing a plane-of-polarization rotary member between a polarizing beam splitter and a detection optical system to limit incident illumination beam to a specific polarized beam component. CONSTITUTION:The laser beam incident on a polarizing beam splitter 9 from a laser beam source 4 is limited to P-polarized beam, and the splitter 9 permits the transmission of the almost whole quantity of said incident beam. When the laser beam passes through the next lambda/4 plate 10, a plane-of-polarization rotates by pi/4 to become circular polarized beam. Therefore, the spot beam LAy formed on a wafer W is also circular polarized beam and, at the same time, the reflected beam from the wafer W is preserved as circular polarized beam. When this reflected beam again reversely advances through the plate 10 with respect to illumination beam, linear polarized beam (S polarized beam) wherein the plane of polarization is further rotated by pi/4 is obtained. Therefore, the reflected beam from the water W is almost entirely reflected by the splitter 9 to reach a space filter 14. As a result, the reflected beam from the wafer W returning to the beam source is reduced to an almost negligible value and the generation of back talk is prevented. |
