Feedback method for increasing stability of electron beams

Abstract

Temperature dependency on magnetic field strength of an electron optical element in an electron beam system due to variation of permeability with temperature of a ferromagnetic pole piece subject to radiant heating from another electron optical element is corrected by measurement of pole piece temperature and closed loop control of excitation current of a correction element which may be provided as a portion of a lens, stigmator, deflector or the like. A correction function may be computed to extrapolate correction values from empirically determined correction values or correction values may be retrieved from a memory such as a look-up table. Performance of the electron beam system is improved and constraints on choice of pole piece materials, mounting geometry, relative positioning of electron optical column elements and electron optical column length are relaxed since temperature dependencies of many electron optical elements can be corrected.

Dependencies are inferred from the claim text.