Measurement and endpointing of sample thickness

Patent metadata

Field	Value
Publication number	US-10978272-B2
Application number	US-201916579006-A
Country	US
Kind code	B2
Filing date	Sep 23, 2019
Priority date	Oct 31, 2018
Publication date	Apr 13, 2021
Grant date	Apr 13, 2021

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.

First claim

The invention claimed is:

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 diffraction pattern center of the diffraction pattern image;
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 values 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 obtaining the diffraction pattern image comprises obtaining the diffraction pattern image with a charged particle beam.

3. A method according to claim 2 , wherein obtaining the diffraction pattern image with the charged particle beam comprises obtaining the diffraction pattern image with an electron beam.

4. A method according to claim 1 , wherein determining the slope of the image values comprises determining the slope of the image values radially outwards from the diffraction pattern center.

5. A method according to claim 1 , wherein determining the slope comprises determining the slope of the image values basted at least in part on use of a function:
f ( x,y )= k ·√{square root over (( x−x 0 ) 2 +( y−y 0 ) 2 )}+ c

wherein:
f=the image values representative for the diffraction pattern;
x,y=coordinates of the diffraction pattern image;
x 0 , y 0 =the diffraction pattern center;
k=the slope; and
c=a constant.

6. A method according to claim 5 , wherein determining the slope of the image values comprises determining the slope of an Electron Count (EC), wherein the EC is used as image values representative for the diffraction pattern, such as in form of f(x,y)=log(log(EC(x,y))).

7. A method according to claim 5 , wherein determining the slope of the image values comprises fitting the diffraction pattern image of the sample to the function, with k and c as variables.

8. A method according to claim 1 , further comprising the step of determining 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, based at least in part on the function:
k(z)=a ·z −b

wherein:
k=the slope;
z=the thickness; and
a, b=constants.

9. 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.

10. A method according to claim 9 , 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.

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

12. A method according to claim 11 , further comprising the step of establishing an end-point of thinning of the sample, based on the determined thickness.

13. 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 diffraction pattern center of the diffraction pattern image;
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.

14. A dual beam charged particle microscope of claim 13 , wherein the controller is configured to further cause the microscope to determine a diffraction pattern center of the diffraction pattern image.

15. A dual beam charged particle microscope of claim 14 , 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.

16. A dual beam charged particle microscope of claim 13 , 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.

17. A dual beam charged particle microscope of claim 16 , 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.

18. A dual beam charged particle microscope of claim 13 , 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.

Assignees

• Fei Co

Inventors

• Vystavel Tomas
• Stejskal Pavel
• Uncovsky Marek

Classifications

• H01J2237/24578

  Spatial variables, e.g. position, distance · CPC title

• H01J2237/31745

  for preparing specimen to be viewed in microscopes or analyzed in microanalysers · CPC title

• H01J2237/31749

  Focused ion beam · CPC title

• H01J37/304

  Controlling tubes by information coming from the objects {or from the beam}, e.g. correction signals · CPC title

• G01N23/2055

  Analysing diffraction patterns · CPC title