| 摘要 |
PURPOSE:To detect the quantities of displacement of a 1st and a 2nd body by measuring the phase difference between beat signals obtained with diffracted light beams from diffraction gratings which are provided to the 1st and 2nd bodies and have equal grating constants. CONSTITUTION:A signal processing control circuit 7 measures the phase difference between the beat signal sent from a mask P1 detector 60 and the beat signal from a wafer P1 detector 62. The circuit 7 also measures the phase difference between the beat signal sent from a mask P2 detector 61 and the beat signal sent from a wafer P2 detector 63. Then the circuit 7 detects the phase difference between the beat signals from diffraction gratings 10 which has the pitch of masks A and B, i.e. 8mum in this case and the phase difference between the beat signals from diffraction gratings 11 which have the same pitch, i.e. 1.5mum in this case, so the quantity of the relative position shift between the wafers A and B can be measured within a range of 4mum and the quantity of displacement between the bodies A and B is obtained. |
