| 摘要 |
PURPOSE:To improve the accuracy of positioning by preventing an adverse effect on the detection of positions due to the mutual interference of scattered light from each body to be positioned. CONSTITUTION:A lambda/2 board 10 and a lambda/4 board 11 are arranged at the prestage of a polarizing beam splitter 5. The board 10 and the board 11 are turned freely centering around an optical path P, and positioned at desired angles. The board 10 changes the direction of polarized light of projecting light to the direction of polarized light of incident light. The board 11 alters the start of polarized light before and behing a transmission through the board 11. Consequently, elliptically polarized light is changed into linearly polarized light in the desired direction by the functioning of the board 11 and the direction of polarized light by the functioning of the board 10 in reflected light from a wafer 4. Accordingly, light from the wafer 4 is cut completely by a direction reflected signal from a mask 3, thus preventing interference. |
