MEASUREMENT AND ENDPOINTING OF SAMPLE THICKNESS

• US 20200135427A1
• Filed: 09/23/2019
• Published: 04/30/2020
• Est. Priority Date: 10/31/2018
• Status: Active Grant

• Current Assignee: FEI Company (Thermo Fisher Scientific Incorporated)
• Original Assignee: FEI Company (Thermo Fisher Scientific Incorporated)
• Inventors: Vystavel, Tomas, Stejskal, Pavel, Uncovsky, Marek
• Granted Patent: US 10,978,272 B2
• Time in Patent Office: Days
• CPC Class Codes: G01B 11/06 for measuring thickness ; e.g. of sheet material thickness measurement by thermal means G01B21/085
• CPC Class Codes: G01B 15/02 for measuring thickness
• CPC Class Codes: G01N 23/2055 Analysing diffraction patterns
• CPC Class Codes: H01J 2237/24455 Transmitted particle detectors
• CPC Class Codes: H01J 2237/24578 Spatial variables, e.g. position, distance
• CPC Class Codes: H01J 2237/2802 Transmission microscopes
• CPC Class Codes: H01J 2237/30466 Detecting endpoint of process
• CPC Class Codes: H01J 2237/31745 for preparing specimen to be viewed in microscopes or analyzed in microanalysers
• CPC Class Codes: H01J 2237/31749 Focused ion beam
• CPC Class Codes: H01J 37/28 with scanning beams H01J37/268, H01J37/292, H01J37/2955 take precedence
• CPC Class Codes: H01J 37/295 Electron or ion diffraction tubes
• CPC Class Codes: H01J 37/304 Controlling tubes by information coming from the objects or from the beam, e.g. correction signals

Abstract

The invention relates to a method of determining the thickness of a sample. According to this method, a diffraction pattern image of a sample of a first material is obtained. Said diffraction pattern image comprises at least image values representative for the diffraction pattern obtained for said sample. A slope of said image values is then determined. The slope is compared to a relation between the thickness of said first material and the slope of image value of a corresponding diffraction pattern image of said first material. The determined slope and said relation are used to determine the thickness of said sample.

Claims

1. A method of determining the thickness of a sample, comprising the steps of:

obtaining a diffraction pattern image of a sample of a first material, wherein the diffraction pattern image comprises at least image values representative for the diffraction pattern obtained for the sample;

determining a slope of the image values;

providing, for the first material, a relation between the thickness of the first material and the slope of image value of a corresponding diffraction pattern image of the first material; and

using the determined slope and the relation to determine the thickness of the sample.

2. A method according to claim 1, wherein the diffraction pattern image is obtained using a charged particle beam.

3. A method according to claim 2, wherein the charged particle beam is an electron beam.

4. A method according to claim 1, wherein the method further comprises determining a diffraction pattern center of the diffraction pattern image.

5. A method according to claim 4, wherein the slope of the image values is determined radially outwards from the diffraction pattern center.

6. A method according to claim 4, wherein determining the slope comprises use of a function:

f(x, y)=−

k·

√

{square root over ((x−

x₀)²+(y−

y₀)²)}+c

wherein;

f=the image values representative for the diffraction pattern;

x,y=coordinates of the diffraction pattern image;

x₀, y₀=the diffraction pattern center;

k=the slope; and

c=a constant.

7. A method according to claim 6, wherein an Electron Count (EC) is used as image values representative for the diffraction pattern, such as in form of f(x,y)=log(log(EC(x,y))).

8. A method according to claim 6, wherein the diffraction pattern image of the sample is fitted to the function, with k and c as variables.

9. A method according to claim 1, wherein for the relation between the thickness of the first material and the slope of image value of a corresponding diffraction pattern image of the first material, use is made of:

k(z)=a·

z<sup>−

b</sup>

wherein;

k=the slope;

z=the thickness; and

a, b=constants.

10. A method according to claim 1, comprising the steps of:

providing a plurality of samples of a first material having mutually different thicknesses;

obtaining respective diffraction patterns; and

establishing the relation between the thickness of the first material and the slope of image value of a corresponding diffraction pattern image of the first material.

11. A method according to claim 10, wherein the step of providing a plurality of samples of a first material having mutually different thicknesses comprises the step of providing a tapered specimen.

12. A method according to claim 1, further comprising monitoring the thickness of the sample during thinning of the sample.

13. A method according to claim 12, further comprising the step of establishing an end-point of thinning of the sample, based on the determined thickness.

14. A dual beam charged particle microscope comprising:

a sample holder, for holding a sample;

an ion beam column, for producing an ion beam onto the sample for thinning the sample;

an electron beam column, for producing an electron beam onto the sample;

a detector, for detecting radiation emanating from the sample and arranged for obtaining a diffraction pattern of the sample;

a controller, for at least partially controlling operation of the microscope to cause the microscope to;

obtain a diffraction pattern image of a sample of a first material, wherein the diffraction pattern image comprises at least image values representative for the diffraction pattern obtained for the sample;

determine a slope of the image values;

provide, for the first material, a relation between the thickness of the first material and the slope of image value of a corresponding diffraction pattern image of the first material; and

use the determined slope and the relation to determine the thickness of the sample.

15. The dual beam charged particle microscope of claim 14, wherein the sample is a tapered specimen having different thicknesses.

16. A dual beam charged particle microscope of claim 14, wherein the controller is configured to further cause the microscope to determine a diffraction pattern center of the diffraction pattern image.

17. A dual beam charged particle microscope of claim 16, wherein the controller is configured to further cause the microscope to determine the slope of the image values radially outwards from the diffraction pattern center.

18. A dual beam charged particle microscope of claim 14, wherein the controller is configured to further cause the microscope to use the determined slope and the relation to monitor the thickness of the sample during thinning of the sample.

19. A dual beam charged particle microscope of claim 18, wherein the controller is configured to further cause the microscope to establish an end-point of thinning of the sample, based on the determined thickness.

20. A dual beam charged particle microscope of claim 14, wherein the controller is configured to further cause the microscope to:

receive an additional sample of the first material; and

use the determined slope and the relation to monitor the thickness of the additional sample during thinning of the additional sample.