Emission noise correction of a charged particle source

A method of operating a charged particle microscope comprising the following steps: - Providing a specimen on a specimen holder; - Using a source to produce a beam of charged particles that is subject to beam current fluctuations; - Employing a beam current sensor, located between said source and specimen holder, to intercept a part of the beam and produce an intercept signal proportional to a current of the intercepted part of the beam, the beam current sensor comprising a hole arranged to pass a beam probe with an associated probe current; - Scanning said probe over the specimen, thereby irradiating the specimen with a specimen current, with a dwell time associated with each scanned location on the specimen; - Using a detector to detect radiation emanating from the specimen in response to irradiation by said probe, and producing an associated detector signal; - Using said intercept signal as input to a compensator to suppress an effect of said current fluctuations in said detector signal, wherein: - The beam current sensor is configured as a semiconductor device with a sensing layer that is oriented toward the source, in which: –ª Each charged particle of said intercepted part of the beam generates electron/hole pairs in said sensing layer; –ª Generated electrons are drawn to an anode of the semiconductor device; –ª Generated holes are drawn to a cathode of the semiconductor device, thereby producing said intercept signal.