| 摘要 |
PURPOSE:To detect a change in a focal position without being affected by a change in the brightness of a light source by a method wherein a first optical system whose quantity of detection light from the light source is changed according to the change in the focal position is installed, a second optical system whose quantity of detection light from the light source is not affected by a change in the focal position is installed and the ratio regarding the quantity of detection light of the first optical system to the second optical system is found. CONSTITUTION:When the brightness of a light source 4 is designated as I, signal levels detected when light has been transmitted through a fiducial mark 12 at a transmittance of k1 and a reference fiducial mark 15 at a transmittance of k2 and when it has been incident individually on a calibration sensor 13 and a reference sensor 16 are respectively k1XI and k2XI. Then, a calibration signal is obtained in an arithmetic circuit. That is to say, the calibration signal does not contain the brightness I of the light source 4, and it is expressed by the ratio regarding the transmittance of the fiducial mark 12 to the reference fiducial mark 15. Then, when the calibration signal is at a peak, the height position of a Z-stage 1 is found. |
