| 摘要 |
PURPOSE:To measure the distance between linear patterns of a plurality of markings in each wafer using an optical means by providing for each identifiable wafer and at different intervals, the markings of the linear patterns which are in parallel with each other in the prescribed ranges distributed on the wafer surface, and the wafers are discriminated automatically. CONSTITUTION:The pattern of markings 20 is printed on an accurate position while the position of a reticle 30 is being ascertained by an attached laser length-measuring device. A wafer is discriminated by the mutual distance D of the marking 20. In order to discriminate the wafer 1 on which the markings 20 are provided, the reflected light coming from the markings 20 is detected by a photo-sensor while the spot of laser beam scans the wafer 1, the wafer is discriminated by correctly computing the time difference, generated by two detected pulses, corresponding to the two markings 20, by a high frequency clock pulse. The laser beam spot can be scanned at a fixed high speed using the means such as reflection and the like of a rotary mirror, and the mutual distance D of the markings 20 can be measured with a high precision. |
