Method of operating a scanning electron microscope

• US 8,227,752 B1
• Filed: 02/17/2011
• Issued: 07/24/2012
• Est. Priority Date: 02/17/2011
• Status: Active Grant

• Current Assignee: CARL Zeiss SMT GmbH (Carl-Zeiss-Stiftung)
• Original Assignee: CARL Zeiss SMT GmbH (Carl-Zeiss-Stiftung)
• Inventors: Mantz, Hubert, Paluszynski, Jaroslaw
• Primary Examiner(s): Wells, Nikita
• Application Number:
  US13/029,998
• Time in Patent Office: 523 Days
• Field of Search: 250/306, 250/307, 250/310, 250/311, 250/492.2
• US Class Current: 250/306
• CPC Class Codes: H01J 2237/226 Image reconstruction
• CPC Class Codes: H01J 2237/2611 Stereoscopic measurements and/or imaging
• CPC Class Codes: H01J 37/28 with scanning beams H01J37/268, H01J37/292, H01J37/2955 take precedence

Abstract

A method of inspecting an object using a scanning particle beam microscope, the method comprising: operating the microscope in a high-resolution mode by laterally scanning a particle beam of the high-resolution mode; operating the microscope in a 3D-mode for acquiring a three-dimensional representation of the object by laterally scanning a particle beam of the 3D-mode; wherein the particle beam of the high-resolution mode and the particle beam of the 3D-mode have a same beam energy and a same focus distance; and wherein an aperture angle of the particle beam of the 3D-mode is at least 2 times greater, or at least 5 times greater, or at least 10 times greater, or at least 100 times greater than an aperture angle of the particle beam of the high-resolution mode.

Claims

1. A method of inspecting an object using a scanning particle beam microscope, the method comprising:

operating the microscope in a high-resolution mode by laterally scanning a particle beam of the high-resolution mode;

operating the microscope in a 3D-mode for acquiring a three-dimensional representation of the object by laterally scanning a particle beam of the 3D-mode;

wherein a beam energy of the particle beam of the high-resolution mode is equal to a beam energy of the particle beam of the 3D-mode and wherein a focus distance of the particle beam of the high-resolution mode is equal to a focus distance of the particle beam of the 3D-mode; and

wherein an aperture angle of the particle beam of the 3D-mode is at least 2 times greater, or at least 5 times greater, or at least 10 times greater, or at least 100 times greater than an aperture angle of the particle beam of the high-resolution mode.

2. The method of claim 1, wherein the aperture angle of the particle beam of the 3D-mode is greater than 2 mrad, or greater than 5 mrad, or greater than 10 mrad, or greater than 100 mrad.

3. The method of claim 1, wherein an object plane of the particle beam of the high-resolution mode is the only plane of the particle beam of the high-resolution mode which is located downstream of a particle beam source and which is optically conjugate to the particle beam source.

4. The method of claim 1, wherein the laterally scanning of the particle beam of the 3D-mode comprises laterally scanning the particle beam of the 3D-mode at each of a plurality of focus distances of the 3D-mode;

wherein the plurality of focus distances comprise the focus distance of the particle beam of the 3D-mode which is equal to the focus distance of the particle beam of the high-resolution mode.

5. The method of claim 4, further comprising:

acquiring a plurality of images, which corresponds to the lateral scanning at the plurality of focus distances;

determining from the plurality of images a plurality of stacks of image regions, such that image regions which are part of a same stack of the plurality of stacks show a same object portion; and

determining for each stack of the plurality of stacks an in-focus region from the image regions of the respective stack.

6. The method of claim 1, further comprising:

determining data values depending on signals generated by a detector of the scanning particle beam microscope; and

determining for each of the data values a location relative to the three-dimensional representation wherein the location corresponds to an object portion at which the respective data value has been measured.

7. The method of claim 1, further comprising:

storing the three-dimensional representation; and

storing a position of a measurement location relative to the three-dimensional representation.

8. The method of claim 7, further comprising:

acquiring a second three-dimensional representation of the object by the operating of the microscope in the 3D-mode; and

comparing the second three-dimensional representation with the stored three-dimensional representation to determine a position of the measurement location relative to a scanning region of the microscope.

9. A method of acquiring a three-dimensional representation of an object by operating a scanning particle beam microscope in a 3D-mode,

wherein in the 3D-mode, an aperture angle of a particle beam of the 3D-mode, which is directed to the object, is at least 2 times greater, or at least 5 times greater, or at least 10 times greater, or at least 100 times greater than an aperture angle of a particle beam of a high-resolution mode of the microscope;

and

wherein a beam energy of the particle beam of the high-resolution mode is equal to a beam energy of the particle beam of the 3D-mode, and wherein a focus distance of the particle beam of the high-resolution mode is equal to a focus distance of the particle beam of the 3D-mode.

10. A scanning particle beam microscope having a particle optical system,

wherein the particle optical system is configured to be operable in a high-resolution mode by laterally scanning a particle beam of the high-resolution mode;

wherein the particle beam microscope is further configured to be operable in a 3D-mode for acquiring a three-dimensional representation of an object by laterally scanning a particle beam of the 3D-mode;

wherein a beam energy of the particle beam of the high-resolution mode is equal to a beam energy of the particle beam of the 3D-mode and wherein a focus distance of the particle beam of the high-resolution mode is equal to a focus distance of the particle beam of the 3D-mode; and

wherein an aperture angle of the particle beam of the 3D-mode is at least 2 times greater, or at least 5 times greater, or at least 10 times greater, or at least 100 times greater than an aperture angle of the particle beam of the high-resolution mode.

11. The scanning particle beam microscope of claim 10, wherein the aperture angle of the particle beam of the 3D-mode is greater than 2 mrad, or greater than 5 mrad, or greater than 10 mrad, or greater than 100 mrad.

12. The scanning particle beam microscope of claim 10, wherein the particle optical system further comprises a particle beam source, wherein an object plane of the particle beam of the high-resolution mode is the only plane of the particle beam of the high-resolution mode, which is located downstream of the particle beam source and which is optically conjugate to the particle beam source.

13. The scanning particle beam microscope of claim 10, wherein the particle optical system further comprises:

a first magnetic condenser lens having a principal plane; and

an objective lens having a principal plane.

14. The scanning particle beam microscope of claim 13, wherein the particle optical system is configured such that an excitation of the first magnetic condenser lens in the 3D-mode is higher than an excitation of the first magnetic condenser lens in the high-resolution mode.

15. The scanning particle beam microscope of claim 13, wherein the particle optical system is configured such that the particle beam of the 3D-mode comprises a cross-over on the beam path between the principal plane of the first magnetic condenser lens and the principal plane of the objective lens.

16. The scanning particle beam microscope of claim 15, wherein the particle optical system is configured such that the particle beam of the high-resolution mode comprises a cross-over on the beam path between the principal plane of the first magnetic condenser lens and the principal plane of the objective lens;

wherein the particle optical system comprises an aperture stop arranged between the principal plane of the first magnetic condenser lens and the principal plane of the objective lens in the beam path; and

wherein a distance along the optical axis between the aperture stop and the cross-over of the particle beam of the high-resolution mode is greater than a distance along the optical axis between the aperture stop and the cross-over of the particle beam of the 3D-mode.

17. The scanning particle beam microscope of claim 13, wherein the particle optical system further comprises a second magnetic condenser lens which is arranged between the first magnetic condenser lens and the objective lens in the beam path;

wherein an excitation of the first magnetic condenser lens in the 3D-mode is lower than an excitation of the first magnetic condenser lens in the high-resolution mode; and

wherein an excitation of the second magnetic condenser lens in the 3D-mode is higher than an excitation of the second magnetic condenser lens in the high-resolution mode.

18. The scanning particle beam microscope of claim 10, wherein the aperture stop is configured to provide a plurality of different aperture diameters at a position in the beam path;

wherein an aperture diameter for the particle beam of the high-resolution mode is smaller than an aperture diameter for the particle beam of the 3D-mode.

19. The scanning particle beam microscope of claim 10, wherein the particle optical system is configured such that the laterally scanning of the particle beam of the 3D-mode comprises laterally scanning the particle beam of the 3D-mode at each of a plurality of focus distances of the 3D-mode;

wherein the plurality of focus distances comprise the focus distance of the particle beam of the 3D-mode which is equal to the focus distance of the particle beam of the high-resolution mode.

20. The scanning particle beam microscope of claim 19, further comprising:

a detector which is configured to detect particles during the laterally scanning of the particle beam of the 3D-mode and to generate signals depending on the detected particles; and

a computer which is configured to receive the signals of the detector, wherein the computer is configured to generate a plurality of images depending on the signals of the detector, wherein the plurality of images correspond to the plurality of focus distances;

determine from the plurality of images a plurality of stacks of image regions, such that image regions which are part of a same stack of the plurality of stacks show a same object portion; and

to

determine for each stack of the plurality of stacks an in-focus region from the image regions of the respective stack.

21. The scanning particle beam microscope of claim 10, further comprising a computer storage medium which is configured to store the three-dimensional representation and to store a position of a measurement location relative to the three-dimensional representation.

22. The scanning particle beam microscope of claim 21, wherein the computer is further configured to compare a second three-dimensional representation acquired in the 3D-mode with the stored three-dimensional representation to determine a position of the measurement location relative to a scanning region of the scanning particle beam microscope.