| 摘要 |
PURPOSE:To prevent a measuring error caused by the non-uniformity of a surface to be measured and to enhance measuring accuracy, by forming beam having two interference beam components shifted by pi in an interference phase to each other as interference beam and indivisually detecting said interference beam components. CONSTITUTION:Monochromatic laser beam L is divided into two by a half mirror 115 and one beam L1 is allowed to irradiate a surface 5 to be measured and the reflected beam LR' thereof is again reflected by the mirror 15 to advance to the right of a drawing. The other beam L2 is reflected by the reference surface 23 of a reference plate 22 through a lambda/4 plate 20 and the reflected beam LR thereof is again passed through the lambda/4 plate 20 to be again incident to the mirror 15 and, at this time, the phase of a specific polarizing component is shifted by pi as compared with the beam L2. These reflected beams LR', LR interfere with each other and the interference beam I thereof passes through a polarizing beam splitter 25 and polarizing plates 26, 27 to be separated into an interference component I1 polarized in a predetermined direction and an interference component I2 polarized in the direction right-angles to said direction. The intensities of these interference beam components are respectively indivisually detected by optical detection systems 28I, 28II and, on the basis of the intensity difference, the surface roughness of the surface 5 is measured by a CPU 40.
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