Discriminative imaging technique in scanning transmission charged particle microscopy

Patent metadata

Field	Value
Publication number	US-10699872-B2
Application number	US-201916288305-A
Country	US
Kind code	B2
Filing date	Feb 28, 2019
Priority date	Mar 1, 2018
Publication date	Jun 30, 2020
Grant date	Jun 30, 2020

Abstract

A method of imaging a specimen in a Scanning Transmission Charged Particle Microscope, comprising the following steps:
Providing the specimen on a specimen holder; Providing a beam of charged particles that is directed from a source through an illuminator so as to irradiate the specimen; Providing a segmented detector for detecting a flux of charged particles traversing the specimen, which flux forms a beam footprint on said detector; Causing said beam to scan across a surface of the specimen, combining signals from different segments of the detector so as to produce a vector output from the detector at each scan position, and compiling this data to yield an imaging vector field; Mathematically processing said imaging vector field by subjecting it to a two-dimensional integration operation, thereby producing an integrated vector field image of the specimen,

specifically comprising:
Using a confined sub-region of said beam footprint to produce said vector output, and the attendant imaging vector field and integrated vector field image.

First claim

The invention claimed is:

1. A method of imaging a specimen in a Scanning Transmission Charged Particle Microscope, comprising the following steps:
providing a beam of charged particles directed from a source through an illuminator so as to irradiate a specimen;
providing a segmented detector for detecting a flux of charged particles traversing the specimen, which flux forms a beam footprint on said detector;
causing said beam to scan across a surface of the specimen, combining signals from different segments of the detector so as to produce a vector output from the detector at each scan position, and compiling this data to yield an imaging vector field; and
mathematically processing said imaging vector field by subjecting it to a two-dimensional integration operation, thereby producing an integrated vector field image of the specimen, wherein
using a confined sub-region of said beam footprint to produce said vector output, the imaging vector field and integrated vector field image.

2. A method according to claim 1 , wherein:
said detector is embodied as a pixelated detector comprising an array of pixels;
said vector output is compiled by:
comparing pixel values to determine a location for an intensity barycenter of said sub-region of the beam footprint on the detector; and
expressing coordinate positions of said barycenter on the detector.

3. A method according to claim 1 , wherein:
said detector is configured to comprise an annular detection surface sub-divided into multiple sectors of substantially equal area; and
said vector output is compiled by determining a weighted signal from different sectors.

4. A method according to claim 3 , wherein said detector is configured to comprise a set of said annular detection surfaces, in nested concentric arrangement.

5. A method according to claim 1 , wherein selection of said sub-region comprises using an aperture plate in said flux between the specimen and detector.

6. A method according to claim 1 , wherein:
said specimen comprises a variety of elemental constituents having a range of different atomic numbers; and
said sub-region of the beam footprint is selected so as discriminatively register a sub-range of atomic numbers.

7. A method according to claim 6 , wherein:
said sub-region of the beam footprint is a confined central region of said footprint; and
said sub-range of atomic numbers comprises relatively low atomic numbers.

8. A method according to claim 6 , wherein:
said sub-region of the beam footprint is a confined peripheral region of said footprint; and
said sub-range of atomic numbers comprises relatively high atomic numbers.

9. A method according to claim 1 , wherein:
in a first imaging session, a first sub-region is used to as a basis to produce a first integrated vector field image; and
in a second imaging session, a second, different sub-region is used to as a basis to produce a second integrated vector field image.

10. A method according to claim 1 , wherein an integrated vector field image obtained using a first sub-region of the beam footprint is combined with at least one of:
an integrated vector field image obtained using a second, different sub-region of the beam footprint;
an integrated vector field image obtained using the whole beam footprint; and
an Annular Dark Field image of the specimen.

11. A Scanning Transmission Charged Particle Microscope, comprising:
an illuminator, for directing a beam of charged particles from a source onto a specimen;
a segmented detector, for detecting a flux of charged particles traversing the specimen, which flux forms a beam footprint on said detector; and
a controller configured to:
effect scanning motion of said beam across a surface of the specimen;
combine signals from different segments of said detector so as to produce a vector output from the detector at each scan position, and compile this data to yield an imaging vector field;
mathematically process said imaging vector field by subjecting it to a two-dimensional integration operation, thereby producing an integrated vector field image of the specimen; and

use a confined sub-region of said beam footprint to produce said vector output, and the attendant imaging vector field and integrated vector field image.

12. A detector assembly for detecting charged particles, comprising:
a set of individually selectable annular detection surfaces in nested concentric arrangement, each annular detection surface being sub-divided into multiple sectors of substantially equal area; and
a processor configured to compile a vector output by calculating a weighted signal from different sectors, and to process said vector by subjecting it to a two-dimensional integration operation.

Assignees

• Fei Co

Inventors

• Bosch Eric Gerardus
• Lazic Ivan
• Imlau Robert

Classifications

• G01N2223/418

  electron microscope · CPC title

• H01J2237/24495

  Signal processing, e.g. mixing of two or more signals · CPC title

• G01N2223/401

  image processing · CPC title

• G01N23/04

  and forming images of the material · CPC title

• H01J2237/22

  Treatment of data · CPC title