| 摘要 |
PURPOSE:To measure precisely, by varying diameter of laser light flux projected on to an object lens according to the magnitude of the pattern step difference, and by varying focused angle of the laser light flux projected onto the pattern face after focused by the object lens. CONSTITUTION:An optical system 2 with a variable light flux diameter is constituted into a Galileo-type afocal system by a fixed lens 2A mounted in the laser light flux and two movable lenses 2B1, 2B2. When the movable lens 2B1 with a long focal distance is inserted in the optical path, the laser light flux is magnified into the same size as the pupil of the object lens 6. When the lens 2B2 with a long focal distance is retreated outside the optical path and at the same time the movable lens 2B2 with a short focal distance is inserted in the optical path, the laser light flux directing to the object lens 6 has a smaller diameter than the pupil diameter of the object lens 6. Since the light flux projected from the optical system 2 with a variable light flux diameter is a parallel flux, the diameter of the laser light flux when being projected on to the object lens 6 and passing through the pupil position A0, is specified by the optical system 2. |
