Method for optically detecting height of a specimen and charged particle beam apparatus using the same

An apparatus using a charged particle beam, comprising:

• a scanning electron microscope system including an electron beam source, a condenser lens which converges an electron beam emitted from said electron beam source, a deflector which deflects the electron beam converged by said condenser lens, an objective lens which converges said electron beam deflected by said deflector onto a measurement object to irradiate the object with the beam, a secondary electron detector which detects secondary electrons generated from said measurement object irradiated with said electron beam, and an image processing unit which measures a pattern formed on said measurement object based on a secondary electron beam image detected by said secondary electron detector;
• a focus control system including a focus control unit which performs focus control by controlling an excitation current of said objective lens, and an automatic focus control unit which performs automatic focus control of said objective lens according to said secondary electron beam image;
• and
• a height detection optical system including a projection optical unit which projects two-dimensional symmetrical light pattern to said measurement object from a position diagonally above the object, an optical image forming unit which forms an image of the two-dimensional symmetrical light pattern projected on measurement object by the projection optical unit a two-dimensional area sensor which detects said optical image of the two-dimensional light pattern and converts two-dimensional optical image detected by said detection optical unit into an electrical signal, and a height detection unit which detects a height of said measurement object by using information obtained from a converted electrical signal having a symmetrical wave pattern selected from the electrical signal converted from the detected image.