Method for avoiding artefacts during serial block face imaging

• US 9,536,704 B2
• Filed: 09/09/2013
• Issued: 01/03/2017
• Est. Priority Date: 09/28/2012
• Status: Active Grant

• Current Assignee: Carl Zeiss Microscopy GmbH (Carl-Zeiss-Stiftung)
• Original Assignee: Carl Zeiss Microscopy GmbH (Carl-Zeiss-Stiftung)
• Inventors: Langer, Matthias, Arnold, Rainer, Esseling, Markus, Paluszynski, Jaroslaw
• Primary Examiner(s): Logie, Michael
• Application Number:
  US14/021,075
• Publication Number:
  US 20140092230A1
• Time in Patent Office: 1,212 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G01N 2223/401 image processing
• CPC Class Codes: G01N 2223/418 electron microscope
• CPC Class Codes: G01N 23/2251 using incident electron beams, e.g. scanning electron microscopy [SEM]
• CPC Class Codes: H01J 2237/221 Image processing
• CPC Class Codes: H01J 2237/226 Image reconstruction
• CPC Class Codes: H01J 37/222 Image processing arrangements associated with the tube image data processing or generation, in general G06T
• CPC Class Codes: H01J 37/28 with scanning beams H01J37/268, H01J37/292, H01J37/2955 take precedence
• CPC Class Codes: H04N 7/18 Closed-circuit television [CCTV] systems, i.e. systems in which the video signal is not broadcast

Abstract

A method includes capturing a first image of the sample via a detector, wherein the particles of the primary particle beam have a first average energy so that the interaction products detected by the detector predominantly contain sample information from a sample layer lying below the sample surface. The method also includes removing the outermost sample layer with the aid of the cutting device, and capturing a second image of the sample via the detector, wherein the particles of the primary particle beam have a second average energy so that the interaction products detected by the detector predominantly contain sample information from the surface layer of the sample. The method further includes calculating the lateral shift/lateral offset of the sample from a comparison of the first and second images, and compensating for the lateral offset.

Claims

1. A method, comprising:

a) obtaining a first image of a sample based on detected interaction products of a first primary particle beam and the sample, the particles of the first primary particle beam having a first average energy so that the detected interaction products predominantly contain sample information for a sample layer which is a sub-surface layer of the sample lying below a surface layer of the sample;

b) after a), removing the surface layer of the sample via a cutting device to provide a new surface layer of the sample which corresponds to the sub-surface layer in a);

c) after b), exposing the sample to a second primary particle beam generated by the particle source;

d) after c), obtaining a second image of the sample based on detected interaction products of a second primary particle beam and the sample, the particles of the second primary particle beam having a second average energy so that the detected interaction products predominantly contain sample information for the new surface layer of the sample corresponding to the sub-surface layer in a); and

e) after d), calculating a lateral shift of the sample based on a comparison of the first and second images,

wherein the first and the second image predominately contain sample information for the same sample layer.

2. The method of claim 1, further comprising compensating for the lateral shift.

3. The method of claim 1, wherein the interaction products detected in a) and d) comprise primary particles scattered at the sample detected via a BSE detector.

4. The method of claim 1, wherein the first average energy is greater than the second average energy.

5. The method of claim 1, wherein the first average energy is greater than 2 keV.

6. The method of claim 5, wherein the second average energy of the particle beam is less than 2 keV.

7. The method of claim 1, wherein the second average energy of the particle beam is less than 2 keV.

8. The method of claim 1, wherein the first image of the sample contains information from a sample layer which lies 10 nm to 50 nm below the surface of the sample.

9. The method of claim 1, further comprising moving the sample to compensate for the lateral shift.

10. The method of claim 1, further comprising deflecting a primary particle beam to compensate for the lateral shift via a shift of the scanned scanning field.

11. The method of claim 1, comprising compensating for the lateral shift via computational methods during 3D reconstruction after obtaining a series of images of the sample.

12. The method of claim 1, wherein e) comprises cross-correlating the first and second images.

13. The method of claim 1, further comprising:

1) scanning a primary particle beam across the sample while the sample is in a first focal plane to obtain an image of the sample;

2) scanning a primary particle beam across the sample while the sample is in a second plane to obtain an image of the sample, the second focal plane being different from the first focal plane,

3) repeating

     2);

4) calculating a 3D construction on the basis of the images obtained in

     1) through

     3),

5) determining an angle which the primary particle beam and the sample surface form relative to one another; and

6) adjusting the angle between primary particle beam and sample surface so that said angle is approximately 90°

.

14. The method of claim 13, wherein 6) comprises moving the sample and/or varying the focal plane of each individual image during the subsequent attainment of a series of images.

15. The method of claim 1, further comprising:

1) obtaining images of the sample surface, a defined region of the sample surface being scanned by the primary beam;

2) selecting at least three sample regions lying in the outer regions of the obtained image;

3) transforming the image data of the selected sample regions via a frequency-based computation algorithm;

4) evaluating the transformed data and determining the focal plane of the sample regions; and

5) varying the sample position so that an angle between the primary particle beam and the sample surface is approximately an angle of 90°

.

16. The method of claim 1, further comprising:

1) for each point of the sample surface, obtaining a signal of primary particles scattered at the sample surface via a quadrant detector having at least four quadrants which detect independently of one another;

2) on the basis of the obtained signals, calculating and storing the height information for each point on the sample surface;

3) determining a surface roughness;

4) adapting the cutting parameters and cutting the sample;

5) repeating

     1) through

     4); and

6) defining a limit value for assessing the cut quality and excluding those image data which exceed the limit value from the 3D reconstruction.

17. The method of claim 1, further comprising:

1) preparing a first operating state so that a needle is moved into a working position of the needle and the cutting device is moved into a rest position of the cutting device;

2) locally introducing gas at the sample surface via the needle so that the gas is ionized and the charges on the sample surface are compensated for;

3) obtaining at least one image of the sample via the detector;

4) preparing a second operating state by moving the cutting device into its working position and moving the needle into a rest position of the needle; and

5) removing a sample layer with the aid of the cutting device.

18. The method of claim 17, wherein the gas comprises nitrogen.

19. The method of claim 1, wherein the cutting device comprises a blade.

20. The method of claim 19, wherein the blade of the cutting device comprises a diamond blade.

21. The method of claim 19, further comprising:

1) for each point of the sample surface, using a SE detector to obtain a signal of secondary electrons released from the sample due to an interaction of the primary particle beam with the sample;

2) identifying pixels having an overdriven or approximately overdriven output signal of the SE detector; and

3) adapting cutting speed and/or adapting oscillation frequency and/or oscillation amplitude of the blade and cutting the sample with adapted parameters, and/or excluding the image data identified in

     2) from the 3D reconstruction.

22. The method of claim 1, wherein the first average energy is the average energy of all the particles of the first primary particle beam, and the second average energy is the average energy of all the particles of the second primary particle beam.

23. A method, comprising:

a) detecting interaction products of a first primary particle beam and a sample to obtain a first image of a first layer of the sample while the first layer of the sample is a sub-surface layer of the sample which lies below an exposed surface of the sample;

b) after a), removing a portion of the sample so that the first layer of the sample is an exposed layer of the sample;

c) after b), detecting interaction products of a second primary particle beam and the sample to obtain a second image of the first layer of the sample while the first layer is the exposed layer of the sample; and

d) after c), calculating a lateral shift of the sample based on a comparison of the first and second images of the first layer,

wherein the first and second images are both images of the first layer.

24. A method, comprising:

a) obtaining a first image of a sample based on detected interaction products of a first primary particle beam and the sample, the particles of the first primary particle beam having a first average energy so that the detected interaction products predominantly contain sample information for a first layer of the sample, the first layer of the sample being a sub-surface layer of the sample lying below a surface layer of the sample;

b) after a), removing the surface layer of the sample via a cutting device to provide a new surface layer of the sample, the new surface layer of the sample being the same as the first layer of the sample;

c) after b), exposing the sample to a second primary particle beam generated by the particle source;

d) after c), obtaining a second image of the sample based on detected interaction products of a second primary particle beam and the sample, the particles of the second primary particle beam having a second average energy so that the detected interaction products predominantly contain sample information for the first surface layer of the sample; and

e) after d), calculating a lateral shift of the sample based on a comparison of the first and second images.