An apparatus for automatically controlling the magnification factor for a scanning electron microscope.

摘要

The present invention relates to an apparatus for calibrating the magnification of a scanning electron microscope. The microscope includes a generator for generating an electron beam, a scanning signal generator for producing a scanning signal and a unit for scanning the beam. The apparatus is comprised of a calibration object which has a plurality of aligned elements thereon which, when scanned by the electron beam produces a signal having a frequency which has a fundamental periodicity dependent on the spacing of the aligned elements. A detector is provided for detecting the signal and producing an output signal having a data content and the fundamental periodicity. A unit is connected to the detector for determining the fundamental periodicity of the output signal from the entire data content of the output signal. A control unit is provided for producing a desired magnification signal. A generator is connected to the unit for determining the fundamental periodicity of the output signal and to the control unit for producing a correction signal which is derived from the desired magnification signal and the fundamental periodicity of the output signal. A combiner is connected to the generator and the unit for scanning the beam for combining the correction signal and the scanning signal to produce a modified scanning signal which scans the electron beam to produce the desired magnification of the scanning electron microscope.