| 摘要 |
PURPOSE:To save the time for measurement and realize accurate and quick focusing by moving the wafer in vertical for the specified distance for focusing during movement in the horizontal direction to the predetermined region by making use of position data of a plurality of detector at the time of preceding focusing. CONSTITUTION:When a wafer 4 moves upward by the drive of piezo-element 23, amount of drive is detected by air sensor nozzles 34, 35, 36, 37 and an eddy current type position detector 22 and then can also be measured. A differential amplifier 45 sequentially compares amount of drive of wafer by piezoelement 23 detected by the eddy current type position detector 22 and amount of drive indicated by a micro processor 40 and drives wafers until such difference is ranged within the range of error. As a result, surface of wafer 4 is accurately located to the predetermined focusing surface position. As a first detector, a photoelectric reflection type displacement member max be used in addition to the air microsensor displacement meter. As a second detector, measurement can be realized with high accuracy even by using an electrostatic capacitance type displacement meter is addition to the eddy current type displacement meter.
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