Patent Number: 
Section: claims

1. A particle beam apparatus defining an optical axis and comprising:an illuminating system for illuminating an object to be positioned in an object plane with a beam of charged particles which splits into a null beam and higher diffraction orders at said object;an objective arranged along said optical axis for imaging said object illuminated by said illuminating system;said illuminating system being configured to generate, during operation, an annularly-shaped illuminating aperture in a plane fourier transformed to said object plane;said objective having a focal plane facing away from said object plane;a phase-shifting element mounted in said focal plane or a plane conjugated thereto;said phase-shifting element including an einzel lens having first and second outer electrodes arranged along said optical axis and an inner electrode arranged therebetween;said electrodes being arranged and charged with electrical potential, during operation, so as to cause the potential at said optical axis to correspond to the potential at said first and second outer electrodes of said einzel lens; and,wherein said phase-shifting element further comprises an ancillary electrode on or near said optical axis. 2. The particle beam apparatus of claim 1, wherein said ancillary electrode is charged with the potential of said first and second outer electrodes. 3. The particle beam apparatus of claim 2, further comprising a manipulator for holding said ancillary electrode and positioning said ancillary electrode perpendicularly to the direction of said optical axis. 4. The particle beam apparatus of claim 1, wherein said phase-shifting element is configured to impart, during operation, a phase shift to said null beam relative to said higher diffraction orders; and, said phase-shifting element is further configured to, during operation, not influence or only slightly influence said higher diffraction orders running closer to said optical axis than said null beam. 5. A particle beam apparatus defining an optical axis and comprising:an illuminating system for illuminating an object to be positioned in an object plane with a beam of charged particles which splits into a null beam and higher diffraction orders at said object;an objective arranged along said optical axis for imaging said object illuminated by said illuminating system;said illuminating system being configured to generate, during operation, an annularly-shaped illuminating aperture in a plane fourier transformed to said object plane;said objective having a focal plane facing away from said object plane;a phase-shifting element mounted in said focal plane or a plane conjugated thereto;said phase-shifting element including an einzel lens having first and second outer electrodes arranged along said optical axis and an inner electrode arranged therebetween;said electrodes being arranged and charged with electrical potential, during operation, so as to cause the potential at said optical axis to correspond to the potential at said first and second outer electrodes of said einzel lens;wherein said inner electrode comprises a plurality of segments;potentials of opposite polarity are applied to respective ones of each two of said segments lying mutually opposite each other with reference to said optical axis; and,wherein said plurality of segments are electrically insulated from each other. 6. The particle beam apparatus of claim 5, further comprising a deflection system for time sequentially generating said annularly-shaped illumination aperture; said deflection system being mounted in a plane conjugated to said object plane on the side thereof facing toward said illumination system; and, a voltage supply configured to cause a potential to be applied to said segments alternately or rotatingly. 7. The particle beam apparatus of claim 5, wherein said inner electrode comprises two segments lying opposite each other with respect to the optical axis and having respective edges facing toward said optical axis; and, said edges are at different distances from said optical axis. 8. The particle beam apparatus of claim 7, further comprising a deflection system for time sequentially generating said annularly-shaped illumination aperture; said deflection system being mounted in a plane conjugated to said object plane on the side thereof facing toward said illumination system; and, a voltage supply configured to cause a potential to be applied to said segments alternately or rotatingly. 9. A particle beam apparatus defining an optical axis and comprising:an illuminating system for illuminating an object to be positioned in an object plane with a beam of charged particles which splits into a null beam and higher diffraction orders at said object;an objective arranged along said optical axis for imaging said object illuminated by said illuminating system;said illuminating system being configured to generate, during operation, an annularly-shaped illuminating aperture in a plane fourier transformed to said object plane;said objective having a focal plane facing away from said object plane;a phase-shifting element mounted in said focal plane or a plane conjugated thereto;said phase-shifting element including a carrier; and, an annularly-shaped electrode accommodated in said carrier;said annularly-shaped electrode having a side facing away from said optical axis in a radial direction;said electrode having an edge on said side thereof;said edge and said carrier conjointly defining an annular gap therebetween wherein said phase-shifting element imparts a phase shift to the beam of charged particles split into higher diffraction orders in response to a potential applied thereto; and,wherein said phase-shifting element does not influence, or only slightly influences, said null beam. 10. The particle beam apparatus of claim 9, wherein said annularly-shaped electrode is a first annularly-shaped electrode; said phase-shifting element further comprises a second annularly-shaped electrode; and, said first and second annularly-shaped electrodes are electrically insulated from each other. 11. The particle beam apparatus of claim 10, wherein said second annularly-shaped electrode is arranged radially outside of said first annularly-shaped electrode; and said carrier is at a potential and, during operation, said potential of said carrier is applied to said second annularly-shaped electrode; and wherein said particle beam apparatus further comprises a voltage source for applying a potential to said first annularly-shaped electrode deviating from said potential of said carrier. 12. The particle beam apparatus of claim 11, wherein one of said first and second annularly-shaped electrodes comprises a plurality of annularly-shaped segments; and wherein said particle beam apparatus further comprises: a deflection system for time sequentially generating said annularly-shaped illumination aperture; said deflection system being mounted in a plane conjugated to said object plane on the side thereof facing toward said illumination system; and, a voltage supply configured to cause a potential to be applied to said segments alternately or rotatingly. 13. The particle beam apparatus of claim 9, wherein said phase-shifting element comprises a plurality of said annularly-shaped electrodes accommodated in said carrier; said annularly-shaped electrodes have respective sides facing away from said optical axis in a radial direction; said electrodes have respective edges on corresponding ones of said sides thereof; and, said edges and said carrier conjointly define respective annular gaps therebetween. 14. The particle beam apparatus of claim 13, wherein each one of said plurality of annularly-shaped electrodes comprises a plurality of annularly-shaped segments.