| 摘要 |
<p>PURPOSE:To enable precision prealignment of a wafer even if a diameter of the wafer is small by applying modification to an output of a photo detector according to a diameter of the wafer and by amplifying the modified output of the photo detector at a predetermined amplification rate based on the diameter of the wafer. CONSTITUTION:Amplification rate of a variable gain amplifying circuit 24 is set to a selector 29 according to a diameter of a wafer, and an output voltage of a D/A converter 30 is also set. A photo detector 21 receives sensor light which is not shielded at a periphery of the wafer. A generated current is converted to a voltage and output to an amplifier 28 through a low path filter 23. Since the amplification rate of the amplifying circuit 24 and an applied voltage from the D/A converter 30 are set according to a diameter of the wafer, it is possible to detect a fine orientation flat accurately.</p> |
