| 摘要 |
PURPOSE:To achieve an automatic focusing point of high accuracy without providing an optical path length altering unit in an optical system for obliquely detecting a pattern by detecting two patterns provided in parallel toward a perpendicular direction to the oblique direction, and so adjusting a mask position that the two patterns are displaced at focal points of the same distance in opposite directions to obtain the composite focal position. CONSTITUTION:Since patterns 2, 3 provided on a mask 1 have different distances to an objective lens 6, the pattern 2 detects an image focused at a point (a) displaced at (-) focal displacement R-on a sensor and the pattern 3 detects an image focused at a point (b) displaced at (+) focal displacement R+ at the composite focal position. Then, when the mask 1 is sequentially raised from below, the detecting forms at the sequential positions vary from R+ to R, R-. when the mask 1 is disposed at the lower position, the pattern 2 becomes the composite focal point as shown by the detecting waveform R+, becoming acute waveform as compared with the pattern 3. The difference of the peak value ¦P1-P2¦ is, for example, calculated for the detecting waveform, and the position where the value becomes minimum is a composite focal point, thereby easily detecting the focal position. |
