| 摘要 |
PURPOSE:To eliminate the erroneous detection due to a complicated pipe line and a change in the original pressure, to eliminate the erroneous detection due to a dust particle between a substrate and a substrate chuck and, at the same time, to remove the erroneous detection due to a change in the atmospheric pressure by a method wherein, before the substrate is sucked, a slice level to judge a suction state is set by a means to store a pressure value of the air pressure. CONSTITUTION:When a wafer does not exist, a vacuum ON/OFF signal g is set to an ON state 41 and the air pressure inside wafer chucks 2, 3 is lowered to the original pressure. At this stage, a value 42 of an output signal b of pressure sensors 4, 5 is taken into a sample- and-hold amplifier 9 and is stored there. Then, after the air pressure inside the wafer chucks 2, 3 has been restored to the atmospheric pressure and the wafer has been mounted, the air pressure is set again to the original pressure. During this process, the output signal b of the pressure sensors 4, 5 is stabilized at a fixed level 44. This output 44 from the sensor is compared with a slice level d by means of comparators 15, 16 so as to obtain a comparator output h. This comparator output h is read out by a wafer-suction-detecting signal j at the prescribed timing, and the suction rate is judged. For this process, a shift volume 46 is selected in such a way that its level does not cause a shift in the position of the wafer when the wafer is sucked by the wafer chucks 2, 3. By this method, it is possible to eliminate the erroneous detection due to the insufficient suction of the wafer. |
