| 摘要 |
<p>The invention relates to a method and means for automatic focusing and has particular use in semiconductor metrology. The invention concerns the use of two beam sources and a single detector. One of said beam sources is projected forwardly of an image plane of an object to be viewed and the second of said beam sources is projected rearwardly of an image plane of an object to be viewed. The reflections from each of said beams are then passed through a vignetting aperture and onto a single focus detector. Using this arrangement it is possible to efficiently and accurately determine the point of focus.</p> |
