Method of determining a brightness of a charged particle beam, method of determining a size of a source of the charged particle beam, and charged particle beam imaging device

Patent metadata

Field	Value
Publication number	US-12386164-B2
Application number	US-202217966385-A
Country	US
Kind code	B2
Filing date	Oct 14, 2022
Priority date	Oct 14, 2022
Publication date	Aug 12, 2025
Grant date	Aug 12, 2025

Abstract

A method of determining a brightness (B r ) of a charged particle beam ( 11 ) focused by a focusing lens ( 120 ) toward a sample ( 10 ) in a charged particle beam imaging device ( 100 ) is described. The method includes (a) taking one or more images (h f, 1 . . . N ) of the sample with the charged particle beam imaging device; (b) retrieving one or more beam profiles (g f, 1 . . . N ) of the charged particle beam from the one or more images; and (c) determining the brightness (B r ) of the charged particle beam ( 11 ) based on at least the one or more beam profiles (g f , g 1 . . . N ), a probe current (I p ) of the charged particle beam, and a landing potential (LE) of the charged particle beam. Optionally, the brightness (B r ) determined as above can be used for determining a size (D virt ) of a source ( 105 ) of the charged particle beam ( 11 ). Further, a charged particle beam imaging device ( 100 ) configured for any of the methods described herein is provided.

First claim

The invention claimed is:

1. A method of determining a brightness of a charged particle beam focused by a focusing lens toward a sample in a charged particle beam imaging device, the method comprising:
(a) taking one or more images of the sample with the charged particle beam imaging device;
(b) retrieving one or more beam profiles of the charged particle beam from the one or more images; and
(c) determining the brightness of the charged particle beam based on at least the one or more beam profiles, a probe current of the charged particle beam, and a landing potential of the charged particle beam.

2. The method of claim 1 , wherein, in (a), one or more images of the sample are taken when the sample is arranged at one or more defocus distances from a respective beam focus of the charged particle beam, the method further comprising:
determining one or more beam widths from the one or more beam profiles; and
calculating a numerical aperture of the charged particle beam based on the one or more beam widths and the one or more defocus distances,
wherein, in (c), the brightness of the charged particle beam is determined based on at least the numerical aperture, the probe current, and the landing potential.

3. The method of claim 2 , wherein the one or more defocus distances at which the one or more images are taken, or differences between the one or more defocus distances, are known in absolute values, and said absolute values are used for calculating the numerical aperture.

4. The method of claim 2 , wherein the numerical aperture of the charged particle beam is calculated based on an average change of beam width as a function of defocus distance, and optionally a calibration factor.

5. The method of claim 1 , wherein
in (a), at least one image of the sample is taken when the sample is arranged at a beam focus of the charged particle beam,
in (b), a focus beam profile is retrieved from the at least one image, and
in (c), the brightness of the charged particle beam is determined based on at least the focus beam profile, a numerical aperture of the charged particle beam, the probe current, and the landing potential.

6. The method according to claim 5 , wherein a focus spot size of the charged particle beam is retrieved from the focus beam profile, and
in (c), the brightness of the charged particle beam is determined based on the focus spot size, the numerical aperture, the probe current, and the landing potential.

7. The method of claim 6 , wherein, in (c), the brightness is determined by calculation using following formula:

B
r

=

4
⁢

I
p

π
2

⁢

d
geo
2

(
NA
)

2

⁢

(
LE
)

(

Formula
⁢

1

)

wherein NA is the numerical aperture of the charged particle beam, I P is the probe current, LE corresponds to the landing potential, and d geo is a focus spot diameter of the charged particle beam.

8. The method according to claim 5 , comprising:
(c1) simulating a focus beam profile using at least the numerical aperture, the probe current, the landing potential, and an estimated brightness as input parameters to provide a simulated focus beam profile;
(c2) comparing the simulated focus beam profile with the focus beam profile retrieved in (b) for determining a magnitude of a difference therebetween; and
(c3) varying the estimated brightness to provide an updated brightness, and repeating (c1) and (c2) in an iterative process for minimizing said magnitude.

9. The method according to claim 8 , wherein (c1) and (c2) are repeated until a minimized magnitude of the difference between the simulated focus beam profile and the retrieved focus beam profile is obtained, and the updated brightness at that iteration is determined as the brightness of the charged particle beam.

10. The method according to claim 1 , wherein the charged particle beam is an electron beam that has one or more of the following parameter values: the probe current is in a range from 1 nA to 5 nA, the landing potential corresponds to a landing energy in a range from 200 eV to 5 keV, and a numerical aperture of the charged particle beam is in a range from 3 mrad to 10 mrad.

11. The method according to claim 1 , wherein, in (b), retrieving the one or more beam profiles from the one or more images comprises dividing the one or more images in Fourier space by a high-resolution image of the sample in Fourier space, or wherein the one or more beam profiles in (b) are retrieved from the one or more images based on a deconvolution.

12. The method according to claim 1 , wherein, in (a), the charged particle beam is focused by the focusing lens toward the sample such that a focus spot size is brightness-limited, particularly such that a geometric spot size is bigger than each of a diffraction contribution, a chromatic blur contribution, and a spherical blur contribution to the focus spot size of the charged particle beam.

13. The method according to claim 1 , further comprising:
taking a high-resolution image of the sample with a second resolution that is higher than a first resolution of the one or more images taken in (a),
wherein, in (b), the one or more beam profiles of the charged particle beam are retrieved by deconvolving the one or more images with the high-resolution image of the sample.

14. A use of a brightness of a charged particle beam determined according to the method of claim 1 for determining a size of a source of the charged particle beam.

15. A method of determining a size of a source of a charged particle beam in a charged particle beam imaging device, comprising:
generating the charged particle beam with the source;
focusing the charged particle beam toward a sample with a focusing lens;
determining a brightness of the charged particle beam according to the method of claim 1 ; and
determining the size of the source based on at least the brightness, a beam potential of the charged particle beam, a charged particle beam current, and a source opening angle.

16. The method according to claim 15 , wherein the beam potential is caused by a potential difference between the so

Assignees

• Ict Integrated Circuit Testing Ges Fuer Halbleiterprueftechnik Mbh

Inventors

• Breuer John
• Ehberger Dominik
• Firnkes Matthias

Classifications

• G02B21/006

  focusing arrangements; selection of the plane to be imaged · CPC title

• G01N15/0205

  by optical means · CPC title

• G01N2015/03

  Electro-optical investigation of a plurality of particles, the analyser being characterised by the optical arrangement · CPC title

• G02B21/0076

  arrangements using fluorescence or luminescence · CPC title

• H01J37/28

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