Search

CN-117637418-B - Optical autofocus unit and method for autofocus

CN117637418BCN 117637418 BCN117637418 BCN 117637418BCN-117637418-B

Abstract

A charged particle evaluation system may include a column including an opening, an illumination unit configured to scan a region of a sample with an electron beam passing through the opening, and an optical autofocus unit configured to (i) illuminate the sample with a beam of light proximate to the electron beam during scanning of the region with the electron beam, (ii) receive a reflected beam from the sample, (iii) determine a focus state of the electron beam, and (iv) participate in compensation of electron beam defocus.

Inventors

  • S. Lachimi
  • H. Faminib

Assignees

  • 应用材料以色列公司

Dates

Publication Date
20260505
Application Date
20230822
Priority Date
20220823

Claims (16)

  1. 1. A charged particle evaluation system comprising: A post, the post comprising an opening; an illumination unit configured to scan an area of a sample with an electron beam passing through the opening, and An optical autofocus unit configured to (i) illuminate the sample with a beam proximate to the electron beam during scanning of the region with the electron beam, (ii) receive a reflected beam from the sample, (iii) determine a focus state of the electron beam, and (iv) participate in compensation of electron beam defocus; wherein the optical autofocus unit includes a mirror and a sensing unit, the mirror positioned within the post, wherein the mirror is configured to deflect the light beam toward the sample and the reflected light beam toward the sensing unit.
  2. 2. The charged particle evaluation system according to claim 1 wherein the optical autofocus unit is configured to determine a length of an optical path of the reflected light beam, and wherein the determination of the focus state is based on the length of the optical path.
  3. 3. The charged particle evaluation system according to claim 1, wherein the optical autofocus unit is configured to determine (a) a length of an optical path of the reflected light beam, and (b) a tilt angle of the reflected light beam, and wherein the determination of the focus state is based on the length of the optical path and the tilt angle.
  4. 4. The charged particle evaluation system of claim 1, wherein the optical autofocus unit is configured to participate in the compensation of electron beam defocus by sending instructions to a mechanical stage.
  5. 5. The charged particle evaluation system of claim 1, wherein the optical autofocus unit comprises a laser interferometry vibrating meter.
  6. 6. The charged particle evaluation system of claim 1, wherein the optical autofocus unit includes a sensing unit positioned within the column.
  7. 7. The charged particle evaluation system according to claim 1 wherein the optical autofocus unit is configured to participate in the compensation of electron beam defocus by sending instructions to electron optical elements.
  8. 8. A charged particle evaluation system comprising: A post, the post comprising an opening; an illumination unit configured to scan an area of a sample with an electron beam passing through the opening, and An optical autofocus unit configured to (i) illuminate the sample with a beam proximate to the electron beam during scanning of the region with the electron beam, (ii) receive a reflected beam from the sample, (iii) determine a focus state of the electron beam, and (iv) participate in compensation of electron beam defocus; Wherein the optical autofocus unit includes a sensing unit positioned outside of the post, wherein the post includes a window optically coupling the sensing unit to one or more optical elements within the post, and Wherein the one or more optical elements within the column include a mirror configured to deflect the light beam toward the sample and deflect the reflected light beam toward the window.
  9. 9. A method for auto-focusing, the method comprising: Scanning, by an illumination unit, a region of the sample with an electron beam passing through an opening of the column; illuminating the sample with a beam of light proximate to the electron beam by an optical autofocus unit during scanning of the region with the electron beam; receiving, by the optical autofocus unit, a reflected light beam from the sample; Determining a focusing state of the electron beam by the optical autofocus unit, and The optical automatic focusing unit participates in the compensation of electron beam defocus; wherein the optical autofocus unit includes a mirror and a sensing unit, the mirror positioned within the post, wherein the mirror is configured to deflect the light beam toward the sample and the reflected light beam toward the sensing unit.
  10. 10. The method of claim 9, comprising determining, by the optical autofocus unit, a length of an optical path of the reflected light beam, and wherein the determination of the focus state is based on the length of the optical path.
  11. 11. The method of claim 9, comprising determining, by the optical autofocus unit, a length of an optical path of the reflected light beam and a tilt angle of the reflected light beam, and wherein the determination of the focus state is based on the length of the optical path and the tilt angle.
  12. 12. The method of claim 9, wherein the compensating for participating in electron beam defocus comprises sending instructions to an electron optical lens.
  13. 13. The method of claim 9, wherein the optical autofocus unit includes a laser interferometric vibrometer.
  14. 14. The method of claim 9, wherein the optical autofocus unit includes a sensing unit positioned within the post.
  15. 15. A method for auto-focusing, the method comprising: Scanning, by an illumination unit, a region of the sample with an electron beam passing through an opening of the column; illuminating the sample with a beam of light proximate to the electron beam by an optical autofocus unit during scanning of the region with the electron beam; receiving, by the optical autofocus unit, a reflected light beam from the sample; Determining a focusing state of the electron beam by the optical autofocus unit, and The optical automatic focusing unit participates in the compensation of electron beam defocus; Wherein the optical autofocus unit includes a sensing unit positioned outside of the post, wherein the post includes a window optically coupling the sensing unit to one or more optical elements within the post, and The one or more optical elements within the column include a mirror configured to deflect the light beam toward the sample and deflect the reflected light beam toward the window.
  16. 16. A non-transitory computer-readable medium storing instructions that, upon execution by a charged particle evaluation system, cause the charged particle evaluation system to: scanning, by an illumination unit of the charged particle evaluation system, a region of the sample with an electron beam passing through an opening of a column; Illuminating the sample with a beam of light proximate to the electron beam by an optical autofocus unit of the charged particle evaluation system during scanning the region with the electron beam; receiving, by the optical autofocus unit, a reflected light beam from the sample; Determining a focusing state of the electron beam by the optical autofocus unit, and The optical automatic focusing unit participates in the compensation of electron beam defocus; wherein the optical autofocus unit includes a mirror and a sensing unit, the mirror positioned within the post, wherein the mirror is configured to deflect the light beam toward the sample and the reflected light beam toward the sensing unit.

Description

Optical autofocus unit and method for autofocus The present application claims the benefit of U.S. patent application Ser. No. 17/893,836, filed 8/23 at 2022, the entire disclosure of which is incorporated herein by reference for all purposes. Background Scanning Electron Microscopy (SEM) scans the sample surface with a primary electron beam. During scanning, the surface must be at the focus of the SEM. Various samples (such as semiconductor wafers) have surfaces that are not perfectly flat and horizontal-this requires a fast and accurate autofocus solution. Disclosure of Invention A charged particle evaluation system may be provided that may include a column including an opening, an illumination unit configured to scan a region of a sample with an electron beam passing through the opening, and an optical autofocus unit configured to (i) illuminate the sample with a beam proximate to the electron beam during scanning of the region with the electron beam, (ii) receive a reflected beam from the sample, (iii) determine a focus state of the electron beam, and (iv) participate in compensation of an electron beam defocus. A method for auto-focusing may be provided that may include scanning, by an illumination unit, a region of a sample with an electron beam passing through an opening of a column, illuminating, by an optical auto-focusing unit, the sample with a beam proximate to the electron beam during scanning of the region with the electron beam, receiving, by the optical auto-focusing unit, a reflected beam from the sample, determining, by the optical auto-focusing unit, a focus state of the electron beam, and participating, by the optical auto-focusing unit, in compensation of the electron beam defocus. A non-transitory computer readable medium method may be provided that stores instructions that, once executed by a charged particle evaluation system, cause the charged particle evaluation system to scan a region of a sample with an electron beam passing through an opening of a column by an illumination unit of the charged particle evaluation system, illuminate the sample with a beam of light proximate to the electron beam during scanning the region with the electron beam by an optical autofocus unit of the charged particle evaluation system, receive a reflected beam of light from the sample by the optical autofocus unit, determine a focus state of the electron beam by the optical autofocus unit, and participate in compensation of an electron beam defocus by the optical autofocus unit. Drawings The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with sample, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: FIG. 1 shows an example of a system and sample; FIG. 2 shows an example of a system and sample, and Fig. 3 shows an example of a method. It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. Detailed Description In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present disclosure. However, it will be understood by those skilled in the art that embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the embodiments of the present disclosure. The subject matter regarded as the embodiments of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. However, embodiments, organization and method of operation of the present disclosure, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings. It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. Because the illustrated embodiments of the present disclosure may be implemented, for the most part, using electronic components and circuits known to those skilled in the art, details will not be expl