Focusing a charged particle imaging system

Patent metadata

Field	Value
Publication number	US-9099282-B2
Application number	US-201414228191-A
Country	US
Kind code	B2
Filing date	Mar 27, 2014
Priority date	Feb 18, 2011
Publication date	Aug 4, 2015
Grant date	Aug 4, 2015

Abstract

A charged particle beam focusing apparatus includes a charged particle beam generator configured to project simultaneously at least one non-astigmatic charged particle beam and at least one astigmatic charged particle beam onto locations on a surface of a specimen, thereby causing released electrons to be emitted from the locations. The apparatus also includes an imaging detector configured to receive the released electrons from the locations and to form images of the locations from the released electrons. A processor analyzes the image produced by the at least one non-astigmatic charged particle beam and in response thereto adjusts a focus of the at least one non-astigmatic charged particle beam.

First claim

What is claimed is:

1. An apparatus comprising:
a charged particle beam generator configured to project simultaneously at least one non-astigmatic charged particle beam and at least one astigmatic charged particle beam onto locations on a surface of a specimen, thereby causing released electrons to be emitted from the locations;
an imaging detector configured to receive the released electrons from the locations and to form images of the locations from the released electrons; and
a processor, coupled to the imaging detector, configured to analyze a subset of the images, the subset being produced by the at least one astigmatic charged particle beam, and in response thereto to adjust a focus of the at least one non-astigmatic charged particle beam.

2. The apparatus according to claim 1 , wherein one of the locations comprises lines parallel to a given direction, and wherein the charged particle beam generator is configured to project a given astigmatic beam comprised in the at least one astigmatic charged particle beam as an ellipse on the one of the locations so that one of a major axis and a minor axis of the ellipse is parallel to the given direction.

3. The apparatus according to claim 2 , wherein analyzing the subset comprises analyzing an image of the one the locations and determining a focus error metric in response to an ellipticity of the ellipse and a concentration of the lines.

4. The apparatus according to claim 1 , further comprising an irradiation system between the charged particle beam generator and the surface, wherein the charged particle generator is configured to protect the at least one non-astigmatic charged particle beam and the at least one astigmatic charged particle beam via the irradiation system.

5. The apparatus according to claim 1 , wherein the charged particle beam generator is configured to project the at least one non-astigmatic charged particle beam as an array of non-astigmatic charged particle beams.

6. The apparatus according to claim 1 , wherein the charged particle beam generator is configured to project the at least one astigmatic charged particle beam as a plurality of astigmatic charged particle beams.

7. The apparatus according to claim 6 , wherein the charged particle beam generator is configured to project the at least one non-astigmatic charged particle beam as an array of non-astigmatic charged particle beams, and wherein the plurality of astigmatic charged particle beams surrounds the array.

8. The apparatus according to claim 1 , wherein the charged particle beam generator comprises a multi-lens array comprising a multi-aperture array element having an array of non-aberration-forming apertures and a plurality of aberration-forming apertures, and wherein the charged particle beam generator is configured to form the at least one non-astigmatic charged particle beam as non-astigmatic charged particle beams by projecting a charged particle beam via the array of the non-aberration-forming apertures and to form the at least one astigmatic beam as astigmatic charged particle beams projecting the charged particle beam via the plurality of the aberration-forming apertures.

9. The apparatus according to claim 8 , wherein the plurality of aberration-forming apertures surrounds the array of non-aberration-forming apertures.

10. The apparatus according to clam 8 , wherein the non-aberration-forming apertures comprise circular apertures.

11. The apparatus according to claim 8 , wherein a dimension of one of the aberration-forming apertures is at least 2.5 times larger than a dimension of one of the non-aberration-forming apertures.

12. The apparatus according to claim 8 , wherein the aberration-forming apertures comprise at least elliptical apertures.

13. The apparatus according to claim 12 , wherein the at least elliptical apertures comprise two elliptical apertures having different orientations.

14. The apparatus according to claim 13 , wherein the two elliptical apertures are oriented orthogonally to each other.

15. The apparatus according to claim 1 wherein the charged particle beam generator is configured to project the at least one non-astigmatic charged particle beam and the at least one astigmatic charged particle beam as electron beams.

16. The apparatus according to claim 1 , wherein the charged particle beam generator is configured to project the at least one astigmatic charged particle beam to form respective at least one ellipses on respective at least one of the locations.

17. The apparatus according to claim 16 , wherein analyzing the subset comprises analyzing an image of the at least one of the locations and determining a focus error metric in response to ellipticities of the at least one ellipses.

18. The apparatus according to claim 17 , wherein the focus of the at least one non-astigmatic charged particle beam is linearly dependent on the focus error metric.

19. The apparatus according to claim 1 , wherein the at least one astigmatic charged particle beam comprises astigmatism chosen from two-fold astigmatism and three-fold astigmatism.

20. An apparatus, comprising:
a charged particle beam generator configured to project simultaneously at least one non-astigmatic charged particle beam and at least one astigmatic charged particle beam onto locations on a surface of a specimen, thereby causing released electrons to be emitted from the locations;
an imaging detector configured to receive the released electrons from the locations and to form images of the locations from the released electrons;
an aberrating element which is positioned before the imaging detector and which is configured to produce an aberration in the images; and
a processor, coupled to the imaging detector, configured to adjust a focus of the at least one non-astigmatic charged particle beam in response to at least one element of a group of elements comprising the aberration and a subset of the images, the subset being produced by the at least one astigmatic charged particle beam.

21. A method for focusing a beam, the method comprising:
projecting simultaneously at least one non-astigmatic charged particle beam and at least one astigmatic charged particle beam onto locations on a surface of a specimen, thereby causing released electrons to be emitted from the locations;
receiving the released electrons from the locations;
forming images of the locations from the released electrons; and
analyzing the image a subset of the images, the subset being produced by the at least one astigmatic charged particle beam and in response thereto adjusting a focus of the at least one non-astigmatic charged particle beam.

22. The method according to claim 21 , wherein one of the locations comprises lines parallel to a given direction, the method further comprising projecting a given astigmatic beam comprised in the at least one astigmatic charged particle beam as an ellipse on the one of the locations so that one of a major axis and a minor axis of the ellipse is parallel to the given direction.

23. The method according to claim 22 , wherein analyzing the subset comprises analyzing an image of the one of the locations and determining a focus error metric in response to an ellipticity of the ellipse and a concentration of the lines.

24. The method according to claim 21 , wherein the at least one non-astigmatic charged particle beam comprises an array of non-astigmatic charged particle beams.

25. The method according to c

Assignees

• Applied Materials Israel Ltd
• Zeiss Carl Smt Gmbh

Inventors

• Rogers Steven R
• Knippelmeyer Rainer K
• Kemen Thomas
• Schubert Stefan
• Elmaliah Nissim

Classifications

• H01J37/153

  Electron-optical or ion-optical arrangements for the correction of image defects, e.g. stigmators · CPC title

• H01J2237/2817

  Pattern inspection · CPC title

• H01J2237/0453

  multiple apertures · CPC title

• H01J37/222

  Image processing arrangements associated with the tube · CPC title

• H01J37/28

  with scanning beams {(H01J37/268, H01J37/292, H01J37/2955 take precedence)} · CPC title