Determination of spatial distribution of charged particle beams

Patent metadata

Field	Value
Publication number	US-9754360-B2
Application number	US-201514978845-A
Country	US
Kind code	B2
Filing date	Dec 22, 2015
Priority date	Dec 22, 2014
Publication date	Sep 5, 2017
Grant date	Sep 5, 2017

Abstract

A point spread function (PSF) of a focused scanning particle beam of an observation instrument is ascertained by obtaining a first image (reference image) based on a reference instrument, the reference image being an image of an area of a reference standard, obtaining a second image (observed image) of the area of the reference standard, and the observed image obtained using the observation instrument configured with a set of operational parameters that define a probe size for the observation instrument, the probe size being larger than a pixel size of the reference image, and then determining, based on the reference image and the observed image, the PSF of the observation instrument as a component of a convolution of the reference image that provides the observed image.

First claim

The invention claimed is:

1. A method comprising:
ascertaining a point spread function (PSF), of a focused scanning particle beam, of an observation instrument, the ascertaining the PSF comprising:
obtaining a first image, the first image being a reference image obtained based on a reference instrument, and the reference image being an image of an area of a reference standard;
obtaining a second image, the second image being an observed image of the area of the reference standard, and the observed image obtained using the observation instrument configured with a set of operational parameters that define a probe size and associated unknown PSF of the observation instrument, the probe size being larger than a pixel size of the reference image; and
determining, based on the reference image and the observed image, the PSF of the observation instrument as a component of a convolution of the reference image that provides the observed image.

2. The method of claim 1 , wherein obtaining the reference image comprises imaging the area of the reference standard using the reference instrument.

3. The method of claim 1 , wherein obtaining the reference image comprises calculating the reference image theoretically based on properties of the reference instrument, absent measuring the area of the reference standard using the reference instrument.

4. The method of claim 1 , further comprising obtaining the reference standard by selecting or fabricating the standard to emphasize contrast of features of the reference standard relative to their background for a selected imaging mode and resistance to damage or alteration from imaging the reference standard.

5. The method of claim 1 , wherein the determining comprises performing sub-pixel alignment between the reference image and the observed image, the performing the sub-pixel alignment facilitating avoiding errors in the PSF determination.

6. The method of claim 1 , wherein the determining comprises adjusting brightness and contrast of the reference and observed images to be consistent and facilitate error avoidance in determining the PSF.

7. The method of claim 1 , wherein the PSF as a component of the convolution is a mathematical component of the convolution, comprising a matrix or a continuous function.

8. The method of claim 1 , wherein the PSF is expressed in matrix form and wherein the determining comprises transforming the observed image and the PSF in matrix form into a column vector format, and recasting the reference image into a block circulant matrix, to solve for the PSF.

9. The method of claim 1 , wherein the determining comprises recasting a convolution equation accounting for noise into a functional form that is optimizable subject to constraint terms that reduce errors due to unlikely or physically unrealizable determinations of the PSF.

10. The method of claim 1 , wherein the determining comprises selecting collection times for collecting image data for the reference and observed images, the selecting based on beam dwell time per pixel and probe current, and the data collection times providing a desired signal-to-noise ratio in the reference image and the observed image and minimizing one or more of sample drift, contamination, and damage to the sample.

11. The method of claim 1 , wherein the reference image has a pixel size smaller than or substantially the same as a probe size or signal excitation size of a probe of the reference instrument.

12. The method of claim 1 , wherein the reference instrument and the observation instrument are different microscopes.

13. The method of claim 12 , wherein a signal type detected to obtain the reference image based on the reference instrument differs from a signal type detected to obtain the observed image using the observation instrument.

14. The method of claim 1 , wherein the reference instrument and the observation instrument are the same instrument.

15. The method of claim 1 , wherein the focused scanning particle beam comprises electrons, photons, or ions.

16. The method of claim 1 , wherein the observation instrument comprises an electron beam lithography tool.

17. The method of claim 1 , wherein one or more of the reference image and the observed image are obtained based on measuring one or more signals comprising secondary electrons, backscattered electrons, transmitted electrons, specimen current, ions, x-rays or cathodoluminescence emission.

18. A computer system comprising:
a memory; and
a processor in communications with the memory, wherein the computer system is configured to perform a method, the method comprising:
ascertaining a point spread function (PSF), of a focused scanning particle beam, of an observation instrument, the ascertaining the PSF comprising:
obtaining a first image, the first image being a reference image obtained based on a reference instrument, and the reference image being an image of an area of a reference standard;
obtaining a second image, the second image being an observed image of the area of the reference standard, and the observed image obtained using the observation instrument configured with a set of operational parameters that define a probe size and associated unknown PSF the observation instrument, the probe size being larger than a pixel size of the reference image; and
determining, based on the reference image and the observed image, the PSF of the observation instrument as a component of a convolution of the reference image that provides the observed image.

19. A computer program product comprising:
a non-transitory computer readable storage medium readable by a processor and storing instructions for execution by the processor for performing a method comprising:
ascertaining a point spread function (PSF), of a focused scanning particle beam, of an observation instrument, the ascertaining the PSF comprising:
obtaining a first image, the first image being a reference image obtained based on a reference instrument, and the reference image being an image of an area of a reference standard;
obtaining a second image, the second image being an observed image of the area of the reference standard, and the observed image obtained using the observation instrument configured with a set of operational parameters that define a probe size and associated unknown PSF of the observation instrument, the probe size being larger than a pixel size of the reference image; and
determining, based on the reference image and the observed image, the PSF of the observation instrument as a component of a convolution of the reference image that provides the observed image.

20. The method of claim 1 , wherein the associated unknown PSF takes on an unknown and unassumed functional form.

Assignees

• Univ New York State Res Found

Inventors

• Lifshin Eric
• Kandel Yudhishthir

Classifications

• G06T5/003 Primary

  Physics · mapped topic

• H01J37/28

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

• H01J2237/2823

  Resolution · CPC title

• H01J37/263

  Contrast, resolution or power of penetration · CPC title

• H01J2237/3175

  Lithography · CPC title