| 摘要 |
PURPOSE:To detect an original correct position even when a mark for a detecting signal is deformed by mounting a nonlinear amplifying circuit for reducing strain resulting from the deformation of the mark for the detecting signal or a waveform shaping circuit between a detecting means and a mark-position detecting circuit. CONSTITUTION:A photoelectric signal to modulated diffracted beams (l) is outputted from a photoelectric element 10 by a vibration mirror 3. An amplifier 13 amplifies the photoelectric signal only by a fixed quantity, and the amplified photoelectric signal A is inputted to a comparator 14 as a nonlinear type amplifier (or a waveform shaping circuit). The comparator 14 compares predetermined reference voltage Vr outputted from a controller 15 and the photoelectric signal A, and outputs a time system-like binary signal D reaching to a logical value [H] when the photoelectric signal A becomes larger than reference voltage Vr. A phase synchronous detecting circuit 16 as a detecting circuit synchronously rectifies the binary signal D by an oscillation signal (f), and outputs a DC-like detecting signal P corresponding to the positional displacement of the center of the vibration of spot beams and the center of a mark M. The controller 15 controls a motor 17 for driving a stage 7 so that the detecting signal P reaches to zero on the basis of the input of the detecting signal P. |
