| 摘要 |
PURPOSE:To improve the resolution in comparison to a conventional one by detecting contact conditions between a mask and a wafer by an ultrasonic sensor and determining a space between them based on a detection signal so as to determine the space quantity from the wafer surface which is as minute as possible. CONSTITUTION:When a wafer 5 has been carried to a wafer chuck 6, the equalization of the initial preset is done by a calibrator as usual. Then the wafer chuck 6 is pushed up gradually and an ultrasonic generator 1 continues to oscillate until the wafer 5 comes in contact with a mask 3 at the peculiar frequency which is determined by the mask 3 and a mask holder plate 4 and outputs the signals of this oscillation which are accepted by an ultrasonic receiver 2. When the wafer 5 comes in contact with the mask 3, the acoustic impedance from the ultrasonic generator 1 to the ultrasonic receiver 2 changes substantially by an influence of the contact. If the alignment has been finished, the exposure can be done while keeping this state. If the alignment has not been finished yet, the non-contact state must be restored for the alignment. |
