| 摘要 |
PURPOSE:To enhance measuring accuracy, by projecting while light on the surface of an object to be measured from the back surface of a reflecting mirror, which is arranged so that the concave surface thereof is obliquely turned to the surface of the object to be measured, through the hole provided to the center of the reflecting mirror and diffracted light other than zero order is reflected toward an interferometer. CONSTITUTION:A concave reflecting mirror 14 having a circuit hole 16 at the center thereof is arranged obliquely with respect to the wafer 10 on a base 12 and, after the wafer 10 is positioned by a telescope 24, the wafer 10 is irradiated with the white light from a white light source 20 through the hole 16. The regular reflected light from the wafer 10 passes through the circular hole 16 and diffracted light other than zero order becomes beam L1 to be projected on an interferometer 22. The beam L1 is split by a splitter 30 and the beam reflected by a fixed mirror 32 and the moving mirror 34 displaced by a piezoelectric element 40 is condensed to a beam detector 40 by a condensing lens 46. The output of the detector 48 is amplified by an amplifier 50 and filtered by a low-pass filter (LPF) 52 and converted by an A/D converter 54. A controller 58 drives the piezoelectric element 40, and a main peak and a sub-peak are drawn from the moving quantity of the mirror 34 and the output of the beam detector 48 and the interval therebetween is measured. By this method, highly accurate measurement is performed.
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