Measuring method and measuring system for interferometrically measuring the imaging quality

Patent metadata

Field	Value
Publication number	US-10697852-B2
Application number	US-201916242480-A
Country	US
Kind code	B2
Filing date	Jan 8, 2019
Priority date	Jul 8, 2016
Publication date	Jun 30, 2020
Grant date	Jun 30, 2020

Abstract

The imaging quality of an optical imaging system is interferometrically measured. A wavefront measurement has a first imaging scale β1 in a first direction and a second imaging scale β2 in a second, perpendicular direction. The second imaging scale differs from the first imaging scale by a scale ratio (β1/β2)≠1 (anamorphic imaging system). A first measurement structure (MS1) on a first structure carrier arranged on the object side of the imaging system has a two-dimensional mask structure suitable for shaping the coherence of measurement radiation. A second measurement structure (MS2) on a second structure carrier arranged on the image side of the imaging system has a diffraction grating. The first and second measurement structures are mutually adapted, taking account of the scale ratio so that an interference pattern arises upon imaging the first measurement structure onto the second measurement structure using the anamorphic imaging system.

First claim

What is claimed is:

1. A measuring method for interferometrically measuring an imaging quality of an optical imaging system by imaging a pattern arranged in an object surface of the optical imaging system onto an image surface of the optical imaging system, comprising:
arranging a first structure carrier with a first measurement structure in a first region of the object surface of the optical imaging system, wherein the first measurement structure has a two-dimensional mask structure shaping a coherence of measurement radiation;
arranging a second structure carrier with a second measurement structure in a second region of the image surface of the optical imaging system, wherein the second measurement structure has a diffraction grating and wherein the image surface of the optical imaging system is optically conjugate to the object surface of the optical imaging system;
illuminating the first measurement structure with the measurement radiation;
imaging the first measurement structure onto the second measurement structure to generate an interference pattern;
detecting the interference pattern in a spatially resolving manner; and
determining at least one imaging parameter describing the imaging quality of the optical imaging system based on the interference pattern,
wherein the optical imaging system is an anamorphic imaging system which has a first imaging scale β 1 in a first direction and a second imaging scale β 2 in a second direction perpendicular to the first direction, wherein the second imaging scale differs from the first imaging scale by a scale ratio (β 1 /β 2 )≠1, and
wherein the second measurement structure is configured based on the first measurement structure and the scale ratio to generate the interference pattern using the optical imaging system.

2. The measuring method as claimed in claim 1 , wherein the two-dimensional mask structure correlates to the diffraction grating such that a coherence function generated by the two-dimensional mask structure yields a low-disturbance interference pattern that increases interference contrast for used signals and decreases the interference contrast for disturbance signals, wherein the low-disturbance interference pattern is an interference pattern that has lower disturbance signal level than the used signals.

3. The measuring method as claimed in claim 2 , wherein a level of the used signals is at least 20% higher than the level of the disturbance signals.

4. The measuring method as claimed in claim 3 , wherein the level of the used signals is at least one order of magnitude higher than the level of the disturbance signals.

5. The measuring method as claimed in claim 1 , wherein the first measurement structure and the second measurement structure are periodic in the first direction and in the second direction, wherein at least one of the measurement structures has a first periodicity length in the first direction, and wherein a second periodicity length differs from the first periodicity length in the second direction.

6. The measuring method as claimed in claim 5 , wherein a ratio between the larger of the two periodicity lengths and the smaller of the two periodicity lengths is in a range of 1.1 to 2.5.

7. The measuring method as claimed in claim 6 , wherein the ratio between the larger of the two periodicity lengths and the smaller of the two periodicity lengths is in the range of 1.5 to 2.

8. The measuring method as claimed in claim 1 , wherein the first measurement structure has the same periodicity length in the first direction and in the second direction and the second measurement structure has a first periodicity length in the first direction and a second periodicity length in the second direction, said second periodicity length being extended or compressed by a factor other than unity relative to the first periodicity length, or
wherein the second measurement structure has the same periodicity length in the first direction and in the second direction and the first measurement structure has a first periodicity length in the first direction and a second periodicity length in the second direction, said second periodicity length being extended or compressed by a factor other than unity relative to the first periodicity length.

9. The measuring method as claimed in claim 1 , wherein one of the measurement structures is a chequered pattern and the other measurement structure is a rhombic pattern.

10. The measuring method as claimed in claim 1 , wherein one of the measurement structures is a cross grating pattern with square cells and the other measurement structure is a non-square rectangular pattern.

11. The measuring method as claimed in claim 1 , wherein the first measurement structure and the second measurement structure each have a line structure with a multiplicity of straight lines parallel to one another and a periodicity length measured perpendicularly to the lines, wherein a first line structure with a first periodicity length, which is adapted to the first imaging scale, is used for a first measurement in the first direction and a second line structure with a second periodicity length, which is adapted to the second imaging scale, is used for a second measurement in the second direction, wherein the first periodicity length differs from the second periodicity length.

12. The measuring method as claimed in claim 11 , wherein the first measurement and the second measurement are carried out temporally successively, wherein a dedicated structure carrier pair consisting of a first structure carrier and a second structure carrier adapted thereto with corresponding measurement structures are used for each of the measurements.

13. The measuring method as claimed in claim 1 , further comprising carrying out a parallel measurement in which measurements for different field points are carried out simultaneously with a plurality of measurement channels configured to be used contemporaneously.

14. The measuring method as claimed in claim 1 , further comprising carrying out a phase shift operation comprising generating and evaluating a plurality of superimposition patterns at different phase angles, wherein the phase angles are varied by stepwise or continuous shifting of the object-side first structure carrier or by stepwise or continuous shifting of the image-side second structure carrier in a shifting direction, and a phase shift curve of the shifting is adapted to the periodicity of the first measurement structure or of the second measurement structure in the shifting direction.

15. The measuring method as claimed in claim 1 , further comprising carrying out an extinction operation, wherein an interference contrast in a direction not provided for evaluation is suppressed by a rapid movement of the diffraction grating with or without reversal of the movement direction, and an amplitude of the movement is adapted to the grating period of the direction.

16. A measuring system for interferometrically measuring an optical imaging system provided for imaging a pattern arranged in an object surface of the optical imaging system onto an image surface of the optical imaging system, comprising:
a first structure carrier arranged on an object side having the object surface of the optical imaging system with a first measurement structure, which has a two-dimensional mask structure shaping a coherence of measurement radiation;
a second structure carrier arranged on an image side having the image surface of the optical imaging system with a second measurement structure, which has a diffraction grating, wherein the second measurement structure is configured b

Assignees

• Zeiss Carl Smt Gmbh

Inventors

• Wegmann Ulrich

Classifications

• G01J9/0215

  by shearing interferometric methods · CPC title

• G01M11/0264 Primary

  by using targets or reference patterns · CPC title

• G01M11/0271

  by using interferometric methods · CPC title

• G01J2009/0219

  using two or more gratings · CPC title

• G03F7/706

  Aberration measurement · CPC title