| 摘要 |
PURPOSE:To perform high-precision focus position detection by compressing an image optically at right angles to the array direction of light and dark parts of a stripe pattern when detecting the contrast of the stripe pattern. CONSTITUTION:The 1st optical system projects and forms an image of the stripe pattern consisting of light and dark parts combined periodically on a surface t3 to be observed and the 2nd optical system which forms an image of the reflected stripe pattern from the surface 3 to be observed by an array type image sensor 6 consisting of plural photoelectric elements. A contrast detecting circuit 7 is provided which obtains light and dark information corresponding to the stripe pattern from the photoelectric conversion output signal of the sensor 6 and detects the focus position of the object surface 3 from the light and dark difference. Then, the detected image is compressed at right angles to the direction corresponding to the light and dark pattern on the sensor 6 and an image in an area wider than the photodetection surface of the sensor 6 is inputted to eliminate the influence of a pattern formed on a sample surface. |
