Precision electrostatic lens system and method of manufacture

• US 5,241,182 A
• Filed: 11/25/1992
• Issued: 08/31/1993
• Est. Priority Date: 06/18/1991
• Status: Expired due to Term

• Current Assignee: FEI Company (Thermo Fisher Scientific Incorporated)
• Original Assignee: FEI Company (Thermo Fisher Scientific Incorporated)
• Inventors: Martin, Noel A., Gerlach, Robert L.
• Primary Examiner(s): Berman, Jack I.
• Application Number:
  US07/982,242
• Time in Patent Office: 279 Days
• Field of Search: 250/396 R, 313/360.1, 313/361.1
• US Class Current: 250/396.00R
• CPC Class Codes: H01J 2237/06316 Schottky emission
• CPC Class Codes: H01J 2237/12 electrostatic
• CPC Class Codes: H01J 3/027 Construction of the gun or parts thereof H01J3/021 - H01J3/025, H01J3/026 and H01J3/028 take precedence
• CPC Class Codes: H01J 37/065 Construction of guns or parts thereof H01J37/067 - H01J37/077 take precedence
• CPC Class Codes: H01J 9/18 Assembling together the component parts of electrode systems

Abstract

A precision electrostatic lens system is formed from lens electrodes having high precision inner bores by aligning said bores on a ceramic rod, inserting segmented glass spacers between adjacent electrodes, and brazing the combination together to provide a monolithic structure capable of maintaining accurate tolerances.

Claims

1. A method of forming a precision electrostatic lens structure capable of accurately focusing a charged particle beam, said method comprising the steps of:

forming plural metal electrodes with side surfaces adapted for juxtaposition with one another, said electrodes being laterally movable relative to one another for therethrough,

positioning an aligning rod through said bores in a pair of adjacent electrodes so as to be closley received by said bores for aligning the same,

inserting a dielectric spacer member of predetermined thickness between said pair of adjacent electrodes,

inserting brazing material at interfaces between said adjacent electrodes and said spacer member,

urging said adjacent electrodes and said spacer member together and raising the combination of said adjacent electrode, said spacer member and said brazing material as thus urged together to an elevated temperature for a predetermined period of time to secure said adjacent electrodes to said spacer member by brazing,

lowering said temperature and physically removing said aligning rod from said bores which closely received the same.

2. The method according to claim 1 wherein said spacer member is segmented such that segments thereof are separately insertable.

3. The method according to claim 2 wherein the segments of said spacer member are inserted in circumferentially spaced relation to one another.

4. The method according to claim 2 including urging said segments radially inwardly relative to the axis of said bores prior to raising the combination to said elevated temperature.

5. The method according to claim 4 wherein the electrodes of said adjacent pair are provided with axial portions against which said dielectric spacer members are inwardly urged prior to brazing.

6. The method according to claim 1 wherein the materials for said electrodes and said spacer member are selected to have substantially similar thermal coefficients of expansion.

7. The method according to claim 6 wherein said electrodes are formed of a titanium alloy and said spacer member is formed of a material selected from the group consisting of alumina and machinable glass.

8. The method according to claim 1 wherein said adjacent electrodes with said spacer member therebetween are urged together in a stack by weighting said stack.

9. The method according to claim 1 wherein the combination is raised to an elevated temperature in a vacuum oven.

10. A method of forming a precision electrostatic lens structure capable of accurately focusing a charged particle beam, said method comprising the steps of:

forming plurality metal electrodes with side surfaces adapted for accurate juxtaposition with respect to one another,

providing said electrodes with high precision central bores in a direction substantially orthogonal to said side surfaces,

positioning a precision aligning rod through said bores in said electrodes so as to be closely received by said bores for aligning the same while said juxtaposed side surfaces are parallel to one another perpendicular to said rod,

inserting a dielectric spacer member between adjacent electrodes, said spacer member having a predetermined thickness and having parallel opposite surfaces for location in facing relation to juxtaposed side surfaces of adjacent electrodes to define interfaces therewith,

inserting brazing material at said interfaces between said adjacent electrodes and said spacer member,

urging said adjacent electrodes and said spacer member together in close contact with said brazing material,

raising the combination of said electrodes, said spacer member and said brazing material, while said combination is urged together, to an elevated temperature for a predetermined period of time to secure adjacent electrodes to said spacer member by brazing,

lowering said temperature and removing said aligning rod from said bores which closely received the same.

11. The method according to claim 10 wherein said adjacent electrodes and said spacer member therebetween are urged together in a stack by weighting said stack.

12. The method according to claim 10 including inserting at least one additional dielectric spacer member between said adjacent electrodes, including placing said additional spacer member at a different and spaced position about the axis of said bores from the first mentioned spacer member, and providing brazing material between said additional spacer member and said adjacent electrodes prior to raising the combination to said elevated temperature.

13. The method according to claim 12 wherein said dielectric spacer members are urged radially inwardly prior to raising the combination to said elevated temperature.

14. The method according to claim 13 wherein an electrode of said pair of adjacent electrodes is provided with an axial portion against which said dielectric spacer members are radially urged prior to brazing.

15. The method according to claim 13 wherein said dielectric spacer members are urged inwardly with a taut wire located in circumferential grooves in said spacer members.

16. The method according to claim 10 wherein said electrodes are formed of titanium alloy and said dielectric spacer members are formed of material selected from the group consisting of alumina and machinable glass.

17. The method according to claim 10 wherein said spacer member is initially slidable radially with respect to said side surfaces of said electrodes between which it is inserted.

18. The method according to claim 17 wherein said spacer member is urged radially inwardly toward the axis of said bores prior to raising the combination to said elevated temperature.

19. The method according to claim 10 wherein the step of providing said electrodes with high precision central bores comprises providing bores of the same diameter in said electrodes.

20. The method according to claim 10 wherein the step of providing said electrodes with high precision central bores comprising providing bores of progressively changing size with said rod being stepped in exterior diameter to match.

21. A method of forming a precision electrostatic lens structure capable of accurately focusing a charged particle beam, said method comprising the steps of:

forming plural metal electrodes with side surfaces adapted for juxtaposition with respect to one another,

providing said electrodes with precision bores extending therethrough,

positioning a precision aligning rod through said bores in at least a pair of adjacent electrodes so as to be closely received by said bores for aligning the same,

inserting an array of dielectric spacer members of predetermined thickness around the axis of said bores between said pair of adjacent electrodes,

inserting brazing material between said adjacent electrodes and said spacer members,

urging said adjacent electrodes and said spacer members together.

raising the combination of said adjacent electrodes, said spacer members and said brazing material to an elevated temperature to secure said adjacent electrodes to said spacer members, and

removing said rod from said bores which closely received the same.

22. The method according to claim 21 wherein said dielectric spacer members are urged radially inwardly prior to raising the combination to said elevated temperature.

23. The method according to claim 22 wherein said dielectric spacer members are urged inwardly with tensioned circumferential means disposed around said spacer members.

24. A precision electrostatic lens structure for accurately focusing a charged particle beam, said structure comprising:

plural metal electrodes with juxtaposed side surfaces and aligned central bores adapted to pass a charged particle beam,

wherein electrodes of at least a pair of said electrodes are joined together by means of plural segmented dielectric spacer members circumferentially spaced from one another about the axis of said bores and brazed to side surfaces of said electrodes,

said metal electrodes and said spacer members having substantially matching thermal coefficients of expansion.

25. The structure according to claim 24 wherein said side surfaces are parallel where they are joined together by said spacer members, said spacer members having matching parallel faces, said side surfaces and said matching faces being substantially perpendicular to the axis of said aligned central bores.

26. The structure according to claim 24 wherein an electrode of said pair of electrodes is provided with an axial portion which said segmented dielectric spacer members are positioned against.

27. The structure according to claim 26 wherein another electrode of said pair of electrodes has a larger diameter cylindrical portion at least partially overlaying said axial portion.

28. The structure according to claim 24 including three electrodes.

29. The structure according to claim 28 wherein the coefficients of thermal expansion of said electrodes and said spacer members are substantially matched.

30. The structure according to claim 24 wherein said structure is monolithic being supportable solely at one end thereof.

31. A precision electrostatic lens structure for accurately focusing a charged particle beam, said structure comprising:

plural metal electrodes with juxtaposed side surfaces and aligned central bores adapted to pass a charged particle beam,

wherein electrodes of at least a pair of said electrodes are joined together with segmented dielectric spacer members,

said side surfaces being parallel where they are joined together by said spacer members, said spacer members having matching parallel faces, said side surfaces and said matching faces being substantially perpendicular to the axis of said aligned central bores.

32. The structure according to claim 31 wherein said electrodes and said spacer members are brazed together.

33. The structure according to claim 31 including three electrodes.

34. The structure according to claim 31 wherein an electrode of said pair of electrodes is provided with an axial portion against which a said spacer member is positioned, and

another electrode of said pair has a larger diameter cylindrical portion at least partially overlaying said axial portion.