| 摘要 |
PURPOSE:To execute a measurement through an optical system related to a main function of a device, and to discriminate directly whether a focus is matched to a use area of an object to be inspected, so as not to be subject to restriction, by detecting the focus by utilizing an image surface characteristic of the optical system. CONSTITUTION:When it is supposed that a wafer W has been placed so as to coincide with the surface on which a mask image has been formed, a pattern P1w and P2w are provided on the wafer W corresponding to a position of a height of Y1 and Y2 which have swung up and down an image height by an equal quantity DELTAy against the best image height Y. This optical system PS is an unmagnification system, therefore, an image of a pattern is formed at a point P1 and P2 of the image height Y1 and Y2 by the same measure even on a mask Ma. A photodetector executes a measurement at a position of P1 and P2, therefore, an out-of-focus pattern image by a portion of a defocus quantity (DELTAz) in the direction of the optical axis is measured, respectively. A slit of the same shape as the pattern is placed in front of the photodetector, therefore, a light quantity indicated by an oblique line part is photodetected. In this case, a difference of outputs of both photodetecting areas is ''0'' because each defocus quantity is equal (P1A=P2B). In this way, the mask image can be focused exactly on the wafer. |
