Method for Axial Alignment of Charged Particle Beam and Charged Particle Beam System

• US 20120119107A1
• Filed: 11/16/2011
• Published: 05/17/2012
• Est. Priority Date: 11/16/2010
• Status: Active Grant

• Current Assignee: JEOL Limited
• Original Assignee: JEOL Limited
• Inventors: Sawada, Hidetaka, Sasaki, Takeo
• Granted Patent: US 8,847,172 B2
• Time in Patent Office: Days
• US Class Current: 250/396.ML
• CPC Class Codes: H01J 2237/103 characterised by lens type
• CPC Class Codes: H01J 2237/1501 Beam alignment means or procedures
• CPC Class Codes: H01J 2237/1532 Astigmatism
• CPC Class Codes: H01J 2237/262 Non-scanning techniques
• CPC Class Codes: H01J 37/1471 for centering, aligning or positioning of ray or beam
• CPC Class Codes: H01J 37/153 Electron-optical or ion-optical arrangements for the correction of image defects, e.g. stigmators
• CPC Class Codes: H01J 37/26 Electron or ion microscopes; Electron or ion diffraction tubes

Abstract

A method for axial alignment of a charged particle beam relative to at least three stages of multipole elements and a charged particle beam system capable of making the axial alignment. Some parts of the orbit of the beam or the distributions of three astigmatic fields, or both, are simultaneously translated in a direction perpendicular to the optical axis such that astigmatisms of the same order and same type due to axial deviations between successive ones of the astigmatic fields cancel.

Claims

1. A method of making axial alignment of a charged particle beam in a charged particle beam system, said method comprising the steps of:

producing at least three astigmatic fields; and

translating parts of the orbit of the charged particle beam or distributions of the astigmatic fields, or both, simultaneously along a direction perpendicular to an optical axis such that astigmatisms of the same order and same type due to axial deviations between successive ones of the astigmatic fields cancel out each other.

2. A method of making axial alignment of a charged particle beam as set forth in claim 1, wherein each of said astigmatic fields is a three-fold astigmatic field, and wherein each of said astigmatisms is a two-fold or five-fold astigmatism.

3. A method of making axial alignment of a charged particle beam as set forth in claim 2, wherein each of said astigmatic fields is the two-fold astigmatic field, and wherein the translating step is terminated when the charged particle beam exiting from the astigmatic field distributed on the most downstream side of the at least three astigmatic fields is most overfocused.

4. A method of making axial alignment of a charged particle beam as set forth in any one of claims 1 to 3, further comprising the step of producing a pair of rotationally symmetric fields between any adjacent two of the astigmatic fields to transfer planes equivalent to planes formed by the astigmatic fields to their downstream astigmatic fields, and wherein parts of the orbit of the charged particle beam, distributions of the astigmatic fields, distributions of the pairs of rotationally symmetric fields, or some of them, are translated simultaneously along a direction perpendicular to the optical axis.

5. A method of making axial alignment of a charged particle beam in a charged particle beam system, said method comprising the steps of:

producing at least 3 three-fold astigmatic fields;

producing a pair of rotationally symmetric fields between any adjacent two of the astigmatic fields to transfer planes equivalent to planes formed by the astigmatic fields to their downstream astigmatic fields; and

simultaneously performing first deflections to cause parts of the orbit of the charged particle beam to enter the three-fold astigmatic fields obliquely.

6. A method of making axial alignment of a charged particle beam as set forth in claim 5, wherein said first deflections include translating the charged particle beam relative to other than the three-fold astigmatic field distributed on the most upstream or downstream side of the three-fold astigmatic fields.

7. A method of making axial alignment of a charged particle beam as set forth in any one of claims 5 and 6, further comprising the step of performing a second deflection simultaneously with said first deflections, the second deflection operating to cause the charged particle beam exiting from the three-fold astigmatic field distributed on the most downstream side of said at least 3 three-fold astigmatic fields to propagate on an optical axis.

8. A method of making axial alignment of a charged particle beam in a charged particle beam system, said method comprising the steps of:

producing 3 three-fold astigmatic fields;

producing a pair of rotationally symmetric fields between any adjacent two of the astigmatic fields to transfer planes equivalent to planes formed by the three-fold astigmatic fields to their downstream astigmatic fields; and

varying intensities of the three-fold astigmatic fields simultaneously while maintaining a summation of three-fold astigmatisms produced by the three-fold astigmatic fields at zero at all times.

9. A method of making axial alignment of a charged particle beam as set forth in claim 8, wherein a phase angle difference of approximately (70.5/3)°

is formed between the most upstream three-fold astigmatic field and the most downstream three-fold astigmatic field of said 3 three-fold astigmatic fields.

10. A charged particle beam system comprising:

at least three stages of multipole elements for producing astigmatic fields; and

deflectors mounted between the multipole elements and operating to translate parts of the orbit of a charged particle beam simultaneously along a direction perpendicular to an optical axis such that astigmatisms of the same order and same type due to axial deviations between successive ones of the multipole elements cancel out each other.

11. A charged particle beam system as set forth in claim 10, further comprising pairs of transfer lenses mounted between the multipole elements, and wherein each pair of transfer lenses produces a pair of rotationally symmetric fields to transfer planes equivalent to planes formed by the multipole elements to their downstream multipole elements.

12. A charged particle beam system as set forth in any one of claims 10 and 11, wherein each of said astigmatic fields is a three-fold astigmatic field, and wherein each of said astigmatisms is a two-fold or five-fold astigmatism.

13. A charged particle beam system as set forth in claim 12, wherein each of said astigmatic fields is the two-fold astigmatic field, and wherein said deflectors terminate the simultaneous translational motions when the charged particle beam exiting from the multipole element located on the most downstream side of the at least three stages of multipole elements is most overfocused.

14. A charged particle beam system comprising:

at least three stages of multipole elements for producing astigmatic fields; and

a moving mechanism for translating the at least three stages of multipole elements separately and simultaneously in a direction perpendicular to an optical axis such that astigmatisms of the same order and same type due to axial deviations between successive ones of the multipole elements cancel out each other.

16. A charged particle beam system as set forth in any one of claims 14 and 15, wherein each of said astigmatic fields is a three-fold astigmatic field, and wherein each of said astigmatisms is a two-fold or five-fold astigmatism.

17. A charged particle beam system as set forth in claim 16, wherein each of said astigmatic fields is the two-fold astigmatic field, and wherein said moving mechanism terminates the simultaneous translational motions when the charged particle beam exiting from the multipole element located on the most downstream side of the at least three stages of multipole elements is most overfocused.

15. A charged particle beam system comprising:

at least three stages of multipole elements for producing astigmatic fields;

pairs of transfer lenses mounted between the multipole elements, each pair of transfer lenses producing a pair of rotationally symmetric fields to transfer planes equivalent to planes formed by the multipole elements to their downstream multipole elements; and

a moving mechanism for translating the multipole elements or the transfer lenses, or both, separately and simultaneously in a direction perpendicular to an optical axis such that astigmatisms of the same order and same type due to axial deviations between successive ones of the multipole elements cancel out each other.

18. A charged particle beam system comprising:

at least three stages of multipole elements for producing three-fold astigmatic fields;

pairs of transfer lenses mounted between successive ones of the multipole elements such that each pair of transfer lenses produces a pair of rotationally symmetric fields to transfer planes equivalent to planes formed by the multipole elements to their downstream multipole elements; and

first deflectors mounted between the transfer lenses of each pair and operating to deflect parts of the orbit of the charged particle beam simultaneously so as to hit the optical axis obliquely.

19. A charged particle beam system as set forth in claim 18, wherein said first deflectors excluding the deflectors mounted upstream of the multipole element located on the most upstream or most downstream side operate to translate parts of the orbit of the charged particle beam as well as to deflect the beam as mentioned previously.

20. A charged particle beam system as set forth in any one of claims 18 and 19, further comprising second deflectors for deflecting the charged particle beam exiting from the multipole element located on the most downstream side of said at least three stages of multipole elements to cause the beam to propagate on the optical axis, and wherein the deflections by the first and second deflectors are made at the same time.

21. A charged particle beam system comprising:

three stages of multipole elements for producing three-fold astigmatic fields;

first deflectors mounted upstream of the multipole elements; and

transfer lenses of a pair mounted upstream and downstream, respectively, of the first deflectors and operating to produce a pair of rotationally symmetric fields to transfer planes equivalent to planes formed by the multipole elements to their downstream multipole elements;

wherein the multipole elements vary intensities of the three-fold astigmatic fields simultaneously while maintaining a summation of three-fold astigmatisms produced by the three-fold astigmatic fields at zero at all times.

22. A charged particle beam system as set forth in claim 21, wherein a phase angle difference of approximately (70.5/3)°

is created between the three-fold astigmatic fields produced respectively by the multipole elements located on the most upstream side and on the most downstream side, respectively, of the three stages of multipole elements.