Patent ID: 7692144

Claim:
An electron beam apparatus equipped with a height detection system configured to assess a height of a specimen during use, comprising: an electron beam unit having an electron beam source, electro optical lenses, a table for setting a specimen and controllable in height direction, and a detector for detecting charged particles emanated from the specimen by the irradiation of an electron beam emitted from the electron beam source and converged and deflected by the electro optical lenses; and a height detection system for detecting height of the specimen set on the table while the specimen is irradiated by the electron beam, wherein the height detection system further comprises: an illumination system configured to direct a first and a second beam of light to a surface of the specimen at substantially opposite azimuth angles and at substantially equal angles of incidence while the specimen is irradiated by the electron beam; a collection system configured to collect the first beam of light specularly reflected from the surface of the specimen and to collect the second beam of light specularly reflected from the surface of the specimen while the specimen is irradiated by the electron beam; first and second detectors, wherein the first detector is configured to generate an output signal responsive to the collected first beam of light, and wherein the second detector is configured to generate an output signal responsive to the collected second beam of light while the specimen is irradiated by the electron beam; and a device configured to receive the output signals from the first and second detectors while the specimen is irradiated by the electron beam and to generate a comparison signal from the output signals while the specimen is irradiated by the electron beam, wherein the comparison signal is responsive to the height of the specimen.