Material testing by angle-variable illumination

Patent metadata

Field	Value
Publication number	US-11506485-B2
Application number	US-201916664734-A
Country	US
Kind code	B2
Filing date	Oct 25, 2019
Priority date	Apr 26, 2017
Publication date	Nov 22, 2022
Grant date	Nov 22, 2022

Abstract

An optical system includes an illumination module configured to illuminate a sample object with at least one angle-variable illumination geometry. The optical system includes an imaging optical unit configured to produce an imaged representation of the sample object that is illuminated with the at least one angle-variable illumination geometry on a detector. The optical system includes the detector, which is configured to capture at least one image of the sample object based on the imaged representation. The optical system includes a controller configured to determine a result image based on a transfer function and the at least one image. A method includes illuminating a sample object with at least one angle-variable illumination geometry, imaging the sample object on a detector, based on the imaged representation, capturing at least one image of the sample object, and, based on a transfer function and the at least one image, determining a result image.

First claim

The invention claimed is:

1. An optical system comprising:
an illumination module configured to illuminate a sample object with at least one pair of angle-variable illumination geometries corresponding to different illumination directions, thus implementing an illumination structured in angle space;
an imaging optical unit configured to produce an imaged representation of the sample object that is illuminated with the at least one pair of angle-variable illumination geometries on a detector;
the detector, wherein the detector is configured to capture at least one pair of real-space images of the sample object based on the imaged representation; and
a controller configured to:
determine a transfer function based on the at least one pair of angle-variable illumination geometries;
determine a pairwise difference for each pair of the at least one pair of real-space images;
determine a spectral decomposition of the pairwise difference; and
determine a real-space result image based on the transfer function and the spectral decomposition.

2. The optical system of claim 1 , wherein the illumination module and the detector are arranged in reflected light geometry.

3. The optical system of claim 1 , wherein the illumination module is configured to illuminate the sample object in dark field geometry.

4. The optical system of claim 1 , wherein:
the controller is configured to detect anomalies in the real-space result image and
the anomalies comprise extreme values in contrast of the real-space result image.

5. The optical system of claim 1 , wherein:
the controller is configured to detect anomalies in the real-space result image and
the anomalies comprise deviations from a real-space pattern of the sample object.

6. The optical system of claim 5 , wherein the controller is configured to determine the deviations from the real-space pattern of the sample object based on at least one of the following techniques: Fourier space filtering, autocorrelation, and deviations with respect to a reference image of the real-space pattern.

7. The optical system of claim 1 , wherein:
the imaging optical unit is characterized by an aperture size, N A ;
a lower threshold is defined based on 5% of a maximum value of all absolute values of the transfer function for spatial frequencies between —N A and N A ; and
for spatial frequencies between —N A and N A , each absolute value of the transfer function is greater than the lower threshold.

8. The optical system of claim 1 , wherein:
the imaging optical unit is characterized by an aperture size, N A ;
a lower threshold is defined based on 2% of a maximum value of all absolute values of the transfer function for spatial frequencies between —N A and N A ; and
for spatial frequencies between —N A and N A , each absolute value of the transfer function is greater than the lower threshold.

9. The optical system of claim 1 , wherein:
the imaging optical unit is characterized by an aperture size, N A ;
a lower threshold is defined based on 0.5% of a maximum value of all absolute values of the transfer function for spatial frequencies between — 2N A and 2N A ; and
for spatial frequencies between — 2N A and 2N A , each absolute value of the transfer function is greater than the lower threshold.

10. The optical system of claim 1 , wherein:
the imaging optical unit is characterized by an aperture size, N A and for spatial frequencies between —N A and N A , the transfer function has no local extreme values.

11. The optical system of claim 1 , wherein the transfer function is a step function.

12. The optical system of claim 1 , wherein the transfer function is one of a monotonously increasing function and a monotonously decreasing function.

13. The optical system of claim 12 , wherein the transfer function is at least one of a linear function and a sigmoid function.

14. The optical system of claim 1 , wherein the transfer function has an axis of symmetry that corresponds to an axis of symmetry of the at least one pair of angle-variable illumination geometries.

15. The optical system of claim 1 , wherein:
the imaging optical unit is characterized by an aperture size, N A ;
an upper threshold is defined based on 5% of a maximum value of all absolute values of the transfer function for spatial frequencies between —N A and N A ; and
for spatial frequencies greater than 2N A and for spatial frequencies less than — 2N A , each absolute value of the transfer function is less than the upper threshold.

16. The optical system of claim 1 , wherein:
the imaging optical unit is characterized by an aperture size, N A ;
an upper threshold is defined based on 2% of a maximum value of all absolute values of the transfer function for spatial frequencies between — 2N A and 2N A ; and
for spatial frequencies greater than 2N A and for spatial frequencies less than — 2N A , each absolute value of the transfer function is less than the upper threshold.

17. The optical system of claim 1 , wherein:
the imaging optical unit is characterized by an aperture size, N A ;
an upper threshold is defined based on 0.5% of a maximum value of all absolute values of the transfer function for spatial frequencies between —N A and N A ; and
for spatial frequencies greater than N A and for spatial frequencies less than —N A , each absolute value of the transfer function is less than the upper threshold.

18. The optical system of claim 1 , wherein the controller is configured to determine the real-space result image based on a Tikhonov regularization with inverse Fourier transform.

19. A method comprising:
illuminating a sample object with at least one pair of angle-variable illumination geometries corresponding to different illumination directions, thus implementing an illumination structured in angle space;
producing an imaged representation of the sample object illuminated with the at least one pair of angle-variable illumination geometries on a detector;
based on the imaged representation, capturing at least one pair of real-space images of the sample object;
determining a transfer function based on the at least one pair of angle-variable illumination geometries;
a pairwise difference of the at least one pair of real-space images;
determining a spectral decomposition of the pairwise difference; and
based on the transfer function and the spectral decomposition, determining a real-space result image.

20. The optical system of claim 1 , wherein the transfer function designates a transfer function other than an object transfer function or an optics transfer function.

21. The optical system of claim 1 , wherein the controller is configured to:
determine a ratio of (i) a difference of each pair of the at least one pair of real-space images to (ii) a sum of the two images of the respective pair; and
determine the real-space result image based on the transfer function and the ratio.

Assignees

• Zeiss Carl Industrielle Messtechnik Gmbh
• Zeiss Carl Microscopy Gmbh

Inventors

• Stoppe Lars
• Milde Thomas
• Totzeck Michael

Classifications

• H04N23/56

  provided with illuminating means · CPC title

• G01N21/8806

  Specially adapted optical and illumination features · CPC title

• G01N2021/8905

  Directional selective optics, e.g. slits, spatial filters · CPC title

• G01B11/2513 Primary

  with several lines being projected in more than one direction, e.g. grids, patterns · CPC title

• G01N21/94

  Investigating contamination, e.g. dust (G01N21/85 takes precedence) · CPC title