| 摘要 |
An alignment apparatus includes an illumination source for illuminating an object having a mark, a photoreceptor for receiving light reflected by the object, a converter for digitizing the output signal level of the photoreceptor, a circuit for determining a slice level on the basis of the data digitized by said converter, a device for comparing the digitized data and the slice level to extract a signal relating to the mark and determining the interval between the mark and a reference, and a device for causing relative movement between the object having the mark and the object having the reference mark to place them into alignment with each other.
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