| 摘要 |
PURPOSE:To reduce the noise and perform photoelectric detection of scattered ray efficiently, by combining a shielding screen to cut polarized light and nonscattered light, in an auto-aligner used in the production of ICs, etc. CONSTITUTION:The linearly polarized light from a laser 1 is made to scan on a wafer 13 through the imageing optical system 40 from above a mask 12 by way of an objective lens 11. In this imaging optical system 40 is placed a 1/4 wavelength plate 50, so as to intersect the light directly reflected from the mask 12 and the light returning from the wafer at right angles in the polarizing direction. Installing a polarized beam splitter 51 in the photoelectrical detection system, overlapped both rays are separated from each other to scattered rays and nonscattered rays by using the characteristics of polarization, removing overlaps, and only scattered beams are picked up. The scattered light is detected by a photo detecter 18 through a shielding screen 16 to permit scattered ray to pass and a lens 17. As for the mask signal, the outputs are delivered simultaneously from both channels. As the wafer signal, the output is delivered to the channel of the side to which the reflected light from the wafer reaches. When necessary, the both signals are added by an adder 52, and then taken out together. |
