Patent ID: 6642525
Filing Date: 2003-11-04
Classification: H01J

Abstract:
A magnetic lens assembly for providing a magnetic deflection field for a beam of charged particles, comprising:a focusing lens device for providing a magnetic field which has substantially rotational symmetry in respect of a symmetry axis of the assembly and acts on the beam traversing said magnetic field as a focusing lens with an optical axis; an axis shifting device comprising at least one axis shifting coil for producing a corrective magnetic field which is superposable on the magnetic field provided by the focusing lens device and acts on the beam such that the optical axis is shiftable parallel to the symmetry axis of the assembly, wherein the axis shifting device comprises a first set of axially spaced apart rings which are positioned concentrically in respect of the symmetry axis and are made of a material which is substantially not electrically conductive and has a high magnetic permeability, wherein the at least one axis shifting coil is provided with a plurality of current conductor windings for producing the corrective magnetic field, and wherein the current conductor windings of the axis shifting coil engage around at least one of the rings of the first ring set; and at least one stigmator coil with a plurality of current conductor windings which engage around at least one of the rings of the first and second ring set.