Automated application of drift correction to sample studied under electron microscope

Patent metadata

Field	Value
Publication number	US-12284445-B2
Application number	US-202418437770-A
Country	US
Kind code	B2
Filing date	Feb 9, 2024
Priority date	Aug 16, 2019
Publication date	Apr 22, 2025
Grant date	Apr 22, 2025

Abstract

Methods and systems for calibrating a transmission electron microscope are disclosed. A fiducial mark on the sample holder is used to identify known reference points so that a current collection area and a through-hole on the sample holder can be located. A plurality of beam current and beam area measurements are taken, and calibration tables are extrapolated from the measurements for a full range of microscope parameters. The calibration tables are then used to determine electron dose of a sample during an experiment at a given configuration.

First claim

What is claimed is:

1. A method for measuring electron dose in a sample with a transmission electron microscope (TEM), the method comprising:
locating a fiducial mark on a TEM holder tip, wherein the TEM holder tip includes a through-hole located at a predetermined distance from the fiducial mark and a current collection area located at a predetermined distance from the fiducial mark;
calibrating the TEM for measuring beam area across a range of possible beam areas to generate a calibration table for beam area for the TEM;
calibrating the TEM for measuring beam current across a range of possible beam currents to generate a calibration table for beam current for the TEM; and
measuring electron dose on the sample during an experiment using the calibrated TEM having a defined configuration, wherein the measured electron dose is determined using the calibration table for beam area and the calibration table for beam current.

2. The method of claim 1 , wherein calibrating the TEM for measuring beam area across the range of possible beam areas comprises:
locating the fiducial mark on the TEM holder tip;
translating the TEM to the through-hole of the TEM holder tip based on the location of the fiducial mark;
taking multiple beam area measurements of the TEM, with the multiple beam area measurements corresponding to multiple beam magnifications of the TEM; and
extrapolating the multiple beam area measurements to generate the calibration table for beam area for the TEM.

3. The method of claim 1 , wherein calibrating the TEM for measuring beam current across a range of possible beam currents comprises:
locating the fiducial mark on the TEM holder tip;
translating the TEM to the current collection area of the TEM holder tip based on the location of the fiducial mark;
collecting current using a Faraday cup on the TEM holder tip;
taking multiple beam current measurements of the TEM from the collected current, with the multiple beam current measurements corresponding to multiple configurations of the TEM; and
extrapolating the multiple beam current measurements to generate the calibration table for beam current for the TEM.

4. The method of claim 1 , wherein the defined configuration of the TEM includes spot size, an aperture setting, an intensity or brightness setting, or an accelerating voltage.

5. The method of claim 1 , further comprising correlating measured beam current to beam current reported by a fluorescent screen or camera across a range of TEM configurations to determine a correction factor such that a true beam current value can be determined for a value of fluorescent screen current or camera current for the defined configuration.

6. The method of claim 1 , further comprising reducing an electron dose rate when a critical value for an electron dose rate or a cumulative electron dose has been reached.

7. The method of claim 6 , wherein the electron dose rate is reduced by changing an aperture setting, changing the spot size, changing a beam intensity, or changing the beam current.

8. A microscope control system for measuring electron dose in a sample with a transmission electron microscope (TEM), the system comprising:
a processor configured for:
calibrating the TEM for measuring beam area across a range of possible beam areas to generate a calibration table for beam area for the TEM;
calibrating the TEM for measuring beam current across a range of possible beam currents to generate a calibration table for beam current for the TEM; and
measuring electron dose on the sample during an experiment using the calibrated TEM having a defined configuration, wherein the measured electron dose is determined using the calibration table for beam area and the calibration table for beam current.

9. The microscope control system of claim 8 , wherein calibrating the TEM for measuring beam area across the range of possible beam areas comprises:
translating the TEM to a through-hole of a TEM holder tip based on a location of a fiducial mark on the TEM holder tip;
taking multiple beam area measurements of the TEM, with the multiple beam area measurements corresponding to multiple beam magnifications of the TEM; and
extrapolating the multiple beam area measurements to generate the calibration table for beam area for the TEM.

10. The microscope control system of claim 8 , wherein calibrating the TEM for measuring beam current across a range of possible beam currents comprises:
translating the TEM to a current collection area of a TEM holder tip based on a location of a fiducial mark on the TEM holder tip;
taking multiple beam current measurements of the TEM using readings from an ammeter that reads current collected using a Faraday cup on the TEM holder tip, with the multiple beam current measurements corresponding to multiple configurations of the TEM; and
extrapolating the multiple beam current measurements to generate the calibration table for beam current for the TEM.

11. The microscope control system of claim 8 , wherein the defined configuration of the TEM includes spot size, an aperture setting, an intensity or brightness setting, or an accelerating voltage.

12. The microscope control system of claim 8 , wherein the processor is further configured for correlating measured beam current to beam current reported by a fluorescent screen or camera across a range of TEM configurations to determine a correction factor such that a true beam current value can be determined for a value of fluorescent screen current or camera current for the defined configuration.

13. The microscope control system of claim 8 , wherein the processor is further configured for reducing an electron dose rate when a critical value for an electron dose rate or a cumulative electron dose has been reached.

14. The microscope control system of claim 13 , wherein the electron dose rate is reduced by changing an aperture setting, changing the spot size, changing a beam intensity, or changing the beam current.

15. A transmission electron microscope (TEM) holder tip for measuring electron beam current, the TEM holder tip comprising:
a through-hole for allowing an electron beam to pass through the TEM holder tip;
a current collection area for capturing beam current of the electron beam; and
a fiducial mark positioned a predetermined distance from the collection area and a predetermined distance from the through-hole.

16. The TEM holder tip of claim 15 , wherein the beam current is measured using an ammeter.

17. The TEM holder tip of claim 16 , wherein a path from the current collection area to the ammeter comprises a low-resistance material and is electrically shielded to prevent interference.

18. The TEM holder tip of claim 15 , wherein the TEM holder comprises a material having a low atomic number and low electrical resistivity for minimizing electron backscatter.

19. The TEM holder tip of claim 15 , wherein the TEM holder tip comprises an aperture for minimizing electron backscatter.

20. The TEM holder tip of claim 15 , wherein the current collection area is electrically isolated from a body of the TEM holder tip to avoid leakage.

Assignees

• Protochips Inc

Inventors

• Walden Ii Franklin Stampley
• Damiano Jr John
• Nackashi David P
• Gardiner Daniel Stephen
• Uebel Mark
• Franks Alan Philip
• Jacobs Benjamin
• Friend Joshua Brian
• Marusak Katherine Elizabeth
• Marthe Jr Nelson L
• Larson Benjamin Bradshaw

Classifications

• H01J2237/2594

  Measuring electric fields or potentials · CPC title

• H01J37/20

  Means for supporting or positioning the object or the material; Means for adjusting diaphragms or lenses associated with the support · CPC title

• G06T7/215

  Motion-based segmentation · CPC title

• G06T7/337

  involving reference images or patches · CPC title

• G06T2207/10061

  from scanning electron microscope · CPC title