PARTICLE BEAM APPARATUS FOR SELECTIVELY FORMING AN IMAGE OF A SPECIMEN OR ITS DIFFRACTION DIAGRAM

• US 3,560,739 A
• Filed: 03/26/1969
• Issued: 02/02/1971
• Est. Priority Date: 03/26/1968
• Status: Expired due to Term

• Current Assignee: Otto Wolff
• Original Assignee: Otto Wolff
• Inventors: Wolff, Otto
• Application Number:
  US04/810,698
• Time in Patent Office: 678 Days
• US Class Current: 250/306
• CPC Class Codes: H01J 37/141 Electromagnetic lenses
• CPC Class Codes: H01J 37/295 Electron or ion diffraction tubes

Abstract

Particle beam device for selectively imaging a specimen or a specimen diffraction diagram having a separately energizable electromagnetic diffraction lens located coaxially of the beam axis between the lens gap of objective lens and the projection lens. The diffraction lens is mounted in magnetically insulating relation within the bore of the objective lens which reduces the axial space of the device. The diffraction lens comprises two component lenses that develop opposing magnetic fluxes along the beam axis so that image rotations within the diffraction lens are avoided.

Claims

1. In a particle beam device having a longitudinal optical axis, an apparatus for selectively imaging a specimen or a specimen diffraction diagram, said apparatus comprising beam generating means for issuing particle beams, means for accommodating a specimen in the path of said beams, an objective lens having a lens gap and a lens bore coaxial with said axis and having front and rear focal planes, said rear focal plane being spaced from said beam generating means a larger distance than said front focal plane, said diffraction diagram being imaged in said rear focal plane of said objective lens by the latter, a projection lens having an object plane and being disposed beyond said objective lens coaxially with said axis, and imaging means disposed beyond the specimen locality in coaxial relation to said axis, said imaging means having a separately energizable electromagnetic diffraction lens for transmitting the diffraction diagram imaged in said rear focal plane of the objective lens to said object plane of the projection lens, said diffraction lens being disposed coaxially intermediate said lens gap of the objective lens and said projection lens, said diffraction lens being further disposed within said bore of said objective lens in magnetically insulating relation thereto, said diffraction lens comprising two component lenses of respective image widths coaxially adjacent to each other for developing respective flux linkages directed along said axis in mutually opposed relation, each of said component lenses having a lens gap bisected by a midplane perpendicular to said axis, the axial distance between said midplanes being less than the image width of the component lens closest to the specimen locality.

2. In a particle beam device according to claim 1, said flux linkages having respective values the ratio of which is adequate to substantially compensate image rotations due to the diffraction lens.

3. In a particle beam device according to claim 1, said objective lens and said projection lens each being electromagnetic.

4. A particle beam device according to claim 1, wherein said two lenses of said diffraction lens are two coils for developing said respective flux linkages and said diffraction lens further comprises an iron circuit for conducting said flux linkages, said iron circuit comprising three annular discs disposed in respective planes perpendicular to said axis, said two coils being sequentially disposed intermediate said discs, and a tubular portion disposed in surrounding relation to said coils and being connected to the respective edge surfaces of said discs.

5. In a particle beam device according to claim 4, said iron circuit consisting of material having low remanence.

6. In a particle bEam device according to claim 1, said objective lens being a pole shoe lens having two pole shoe members disposed coaxially in relation to said axis and separated from each other so as to define said lens gap, one of said pole shoe members being disposed beyond the specimen locality and having an opening which widens in a direction extending away from said lens gap so as to form a receptacle for accommodating said diffraction lens.

7. A particle beam device according to claim 6 wherein the particle beam device is provided with a stigmator, said opening being adequate to receive said stigmator, said stigmator being in coaxial relation to said axis and being closer to said lens gap defined by said pole shoe members than said diffraction lens.

8. A particle beam device according to claim 1, wherein said apparatus has an imaging scale for transmitting the diffraction image such that the image of the specimen projected by the objective lens and the image of its diffraction diagram projected by said apparatus are formed with at least substantially the same magnification.

9. In a particle beam device according to claim 8, said imaging scale being at least 1:

1.

10. In a particle beam device according to claim 8, said imaging scale being greater than 1:

1.

11. A particle beam device according to claim 1, wherein said apparatus comprises a selector diaphragm disposed in the object plane of said projection lens.

12. A particle beam device according to claim 1, wherein said apparatus comprises two intermediate lenses, one of said lenses being closer to said beam generating means than the other of said lenses, said projection lens being said one lens of said two intermediate lenses, said two intermediate lenses having respective variable excitations for the entire range of magnification corresponding to a fixed objective lens excitation.

13. In a particle beam device according to claim 12, each of said intermediate lenses having two component lenses for developing respective flux linkages directed along said axis in mutually opposed relation, said flux linkages having respective values the ratio of which is adequate to substantially compensate image rotations.

14. A particle beam device according to claim 1, wherein said apparatus comprises projection means beyond said projection lens, the last lens of said projection means being a projective lens with an interchangeable pole shoe system.

15. A particle beam device according to claim 1, wherein said apparatus comprises vacuum seal means and a base plate, said diffraction lens being mounted on said base plate and extending into said bore of said objective lens, said objective lens having an end face beyond the specimen, said end face abutting said base plate, said seal means being disposed intermediate said base plate and said end face for forming a vacuumtight seal therebetween, said base plate having vacuumtight channels for directing electrical leads to said diffraction lens.

16. In a particle beam device according to claim 15, said apparatus comprising adjusting drive means mounted on said base plate for transverse displacement.

17. A particle beam device according to claim 1, wherein said apparatus comprises a selector diaphragm, disc means disposed adjacent said base plate for shielding stray magnetic fields, said disc means having means for receiving said selector diaphragm, and drive means mounted to said disc means for adjusting said diaphragm, said disc means abutting said projection lens, and a vacuum seal disposed intermediate said disc means and said projection means.

18. In a particle beam device according to claim 15, said diffraction lens being disposed in said bore of said objective lens so as to define gap between said diffraction lens and the latter whereby said gap magnetically insulates said objective lens from said diffraction lens.

19. In a particle beam device according to claim 1, said diffraction lens being adjustable to form an image of the specimen in the object plane of said projection lens with said objective lens being deenergized.

20. In a particle beam device according to claim 19, said objective lens having two excitation coils, said coils being disposed in coaxial relation to said axis and positioned there along to form a space wherein the specimen is laterally insertable.

21. A particle beam device according to claim 19, wherein one of said coils is closer to said beam generating means than the other of said coils, said one coil having a greater number of ampere turns than the other of said coils.

22. In a particle beam device according to claim 21, said objective lens having two pole shoes coaxial with said axis, one of said pole shoes being further from said beam generating means than the other of said pole shoes, said one pole shoe having a bore for receiving said diffraction lens.

23. In a particle beam device according to claim 1, said diffraction lens being adjacent said projection lens and adjustable for transmitting the diffraction diagram into said object plane of the projection lens.

24. In a particle beam device according to claim 1, wherein said diffraction lens has two focal planes, one of said focal planes being further from the specimen locality than the other of said focal planes, and aperture diaphragm is disposed so as to be coincident with said one focal plane, said diaphragm having an aperture dimensioned so that the beam may pass unimpeded when said objective lens is deenergized.