| 摘要 |
PURPOSE:To set the distance between a mask and a wafer with high velocity and high accuracy without any damage by measuring the amplitude of a vibration of either one of a mask or a wafer. CONSTITUTION:When a mask 7 is allowed to vibrate by an oscillator 5, a mask 7 vibrates since the air between the mask 7 and a wafer 6 acts as a damper. The action of the damper changes corresponding to the distance (d) and when the frequency of the oscillator 5 is constant, the amplitude decreases. Accordingly, when the amplitude of the wafer 7 is measured and the hight of the wafer stand 3 is controlled so that it may be equal to the amplitude which corresponds to the optimum distance previously set, the distance (d) is always set accurately. The laser reflects with a scanning line 10 and radiates on the mask 7 and the wafer 2 vertically through the mirror 11, and reflective light thereof is catched by a sensor 12 as an interference light thereof is catched by a senser 12 as an interference light through the mirror 11. The interference light is photoelectric transformed and the vibration and the amplitude of the mask 7 are calculated, whereby the stand 2 is allowed to raise or lowered. By this method, the distance (d) is controlled with high accuracy and high velocity. |
