| 摘要 |
An auto-focusing alignment and measurement system for use in precisely positioning a semiconductor substrate with respect to an integrated circuit mask is herein disclosed. This system includes a moveable convergent lens operable with another pair of convergent lenses for alternately focusing images of the mask and the substrate onto a photodiode array. The photodiode array serves as a focus detector and, together with associated signal processing circuitry, provides a feedback signal for controlling displacement of the moveable lens to equal the separation between the mask and the substrate with an accuracy better than the depth of field of the optics. An illumination source and viewing optics provide a magnified view of images of both the mask and the substrate superimposed and in focus, thereby facilitating alignment of the substrate with respect to the mask prior to photolithographic printing. This apparatus may also be employed to measure the degree of surface flatness and parallelism between the mask and the substrate.
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