Method for three-dimensionally measuring a 3D aerial image of a lithography mask

Patent metadata

Field	Value
Publication number	US-10068325-B2
Application number	US-201715410918-A
Country	US
Kind code	B2
Filing date	Jan 20, 2017
Priority date	Jul 22, 2014
Publication date	Sep 4, 2018
Grant date	Sep 4, 2018

Abstract

In a method for three-dimensionally measuring a 3D aerial image in the region around an image plane during the imaging of a lithography mask, which is arranged in an object plane, a selectable imaging scale ratio in mutually perpendicular directions (x, y) is taken into account. For this purpose, an electromagnetic wavefront of imaging light is reconstructed after interaction thereof with the lithography mask. An influencing variable that corresponds to the imaging scale ratio is included. Finally, the 3D aerial image measured with the inclusion of the influencing variable is output. This results in a measuring method with which lithography masks that are optimized for being used with an anamorphic projection optical unit during projection exposure can also be measured.

First claim

What is claimed is:

1. A method for three-dimensionally measuring a 3D aerial image in the region around an image plane during the imaging of a lithography mask, which is arranged in an object plane, while taking into account a selectable imaging scale ratio in mutually perpendicular directions with the following steps:
reconstruction of an electromagnetic wavefront of imaging light after interaction thereof with the lithography mask,
inclusion of an influencing variable that corresponds to the imaging scale ratio, and
output of the 3D aerial image measured with the inclusion of the influencing variable.

2. The method according to claim 1 , wherein the following steps are carried out in the reconstruction:
measuring a 2D imaging-light intensity distribution in the region of a plane corresponding to the image plane,
displacing the lithography mask perpendicularly to the object plane by a predetermined displacement, and
repeating the “measuring” and “displacing” steps until a sufficient number of 2D imaging-light intensity distributions to reproduce a 3D aerial image are measured.

3. The method according to claim 2 , wherein the measurement is carried out with a measuring optical unit, the imaging scale of which is the same in mutually perpendicular directions, the inclusion of the influencing variable being performed by converting the data of the measured 2D imaging-light intensity distribution.

4. The method according to claim 3 , wherein in the reconstruction of the electromagnetic wavefront, a phase reconstruction is performed.

5. The method according to claim 4 , wherein for the phase reconstruction, a defocusing of the imaging of the lithography mask is varied.

6. The method according to claim 1 , wherein in the reconstruction, a manipulation is performed on the illumination optical unit, with which the lithography mask is illuminated.

7. The method according to claim 1 , wherein for the reconstruction, an illumination pupil of the illumination optical unit is varied.

8. The method according to claim 1 , wherein the inclusion of the influencing variable in the conversion of the data of the wavefront is performed by a digital simulation of the imaging with the imaging scale ratio.

9. The method according to claim 1 , wherein in the reconstruction of the electromagnetic wavefront, an intensity reconstruction is performed.

10. The method according to claim 9 , wherein the intensity reconstruction is carried out with the following steps:
measuring a 2D imaging-light intensity distribution in the region of a plane corresponding to the image plane,
displacing the lithography mask perpendicularly to the object plane by a predetermined displacement,
repeating the “measuring” and “displacing” steps until a sufficient number of 2D imaging-light intensity distributions to reproduce a 3D aerial image are measured, and
carrying out an intensity Fourier transformation of the 2D imaging-light intensity distributions obtained to generate a corresponding number of 2D intensity Fourier transforms.

11. The method according to claim 9 , wherein the intensity reconstruction is carried out with the following steps:
measuring a 2D imaging-light intensity distribution in the region of a plane corresponding to the image plane,
displacing the lithography mask perpendicularly to the object plane by a predetermined displacement,
repeating the “measuring” and “displacing” steps until a sufficient number of 2D imaging-light intensity distributions to reproduce a 3D aerial image are measured, and
distorting the measured 2D imaging-light intensity distributions with the imaging scale ratio.

12. The method according to claim 10 , comprising the following steps:
selecting the directional components of the generated 2D intensity Fourier transforms while taking into account the imaging scale ratio, a displacement during the displacing of the lithography mask perpendicularly to the object plane scaling with the alignment of the directional components, to generate in each case a partial synthetic 2D intensity Fourier transform;
adding the generated partial synthetic 2D intensity Fourier transforms to form an overall synthetic 2D intensity Fourier transform; and
carrying out an inverse intensity Fourier transformation of the overall synthetic 2D intensity Fourier transforms to produce a synthetic raw image.

13. The method according to claim 12 , comprising producing a result image by distorting the synthetic raw image with the imaging scale ratio.

14. The method according to claim 12 , wherein the selection of the directional components of the generated 2D intensity Fourier transforms is performed by multiplying each of the generated 2D intensity Fourier transforms by an assigned selection function for the selection of predetermined angle sectors of the 2D intensity Fourier transforms, the selection function being dependent on the displacement perpendicularly to the object plane and on the imaging scale ratio, to generate the respective partial synthetic 2D Fourier transforms.

15. The method according to claim 14 , comprising using a digital selection function.

16. A metrology system for three-dimensionally measuring a 3D aerial image in the region around an image plane during the imaging of a lithography mask, which is arranged in an object plane, in which the metrology system is configured to take into account a selectable imaging scale ratio in mutually perpendicular directions with the following steps:
reconstruction of an electromagnetic wavefront of imaging light after interaction thereof with the lithography mask,
inclusion of an influencing variable that corresponds to the imaging scale ratio, and
output of the 3D aerial image measured with the inclusion of the influencing variable;

wherein the metrology system comprises:
an illumination optical unit for illuminating the lithography mask to be examined, and
an imaging optical unit for imaging the object towards a spatially resolving detection device.

17. The metrology system of claim 16 , in which the metrology system is configured to carry out the following steps in the reconstruction:
measuring a 2D imaging-light intensity distribution in the region of a plane corresponding to the image plane,
displacing the lithography mask perpendicularly to the object plane by a predetermined displacement, and
repeating the “measuring” and “displacing” steps until a sufficient number of 2D imaging-light intensity distributions to reproduce a 3D aerial image are measured.

18. The metrology system of claim 17 , comprising a measuring optical unit configured to carry out the measurement, the imaging scale of which is the same in mutually perpendicular directions, the inclusion of the influencing variable being performed by converting the data of the measured 2D imaging-light intensity distribution.

19. The metrology system of claim 18 , wherein the system is configured to perform a phase reconstruction in the reconstruction of the electromagnetic wavefront.

20. The metrology system of claim 19 , wherein the system is configured to vary a defocusing of the imaging of the lithography mask for the phase reconstruction.

Assignees

• Zeiss Carl Smt Gmbh

Inventors

• Matejka Ulrich
• Husemann Christoph
• Ruoff Johannes
• Perlitz Sascha
• Mann Hans-Jürgen

Classifications

• G02B13/08

  Anamorphotic objectives · CPC title

• G02B17/0647 Primary

  using more than three curved mirrors (G02B17/0668, G02B17/0694 take precedence) · CPC title

• G02B27/0988

  Diaphragms, spatial filters, masks for removing or filtering a part of the beam · CPC title

• G02B17/0848

  off-axis or unobscured systems in which not all of the mirrors share a common axis of rotational symmetry, e.g. at least one of the mirrors is warped, tilted or decentered with respect to the other elements · CPC title

• G03F1/84

  Inspecting · CPC title