Patent ID: 8466430

Claim:
An electrostatic lens comprising: a plurality of electrodes each having at least one through hole, corresponding ones of the through holes being aligned with each other; and an insulating spacer that is provided between the plurality of electrodes and that fixes an interval between the plurality of electrodes, wherein a protective film is disposed on a surface of each of the plurality of electrodes, the protective film is present on an interior wall of the at least one through hole and in a region around the at least one through hole on the surface of the electrode, the region extending continuously from the interior wall to an end portion of the electrode, and the protective film is not present between the electrode and the spacer, and wherein a distance l (meters) between an end portion of the protective film in the region around the at least one through hole and the center of the at least one through hole satisfies the following expression in the meter-kilogram-second-ampere unit system, l ≧(5×10 3 /3)×( g/φacc )×[−10.5+ln( gΔφ/s )], where a distance between the plurality of electrodes is represented by g (meters), a voltage difference between the plurality of electrodes is represented by Δφ (volts), an absolute value of an acceleration voltage of a charged particle beam is represented by φacc (volts), and an allowed value of a center distance precision for the charged particle beam is represented by s (meters).