Method for determining an imaging quality of an optical system when illuminated by illumination light within a pupil to be measured

Patent metadata

Field	Value
Publication number	US-2022390320-A1
Application number	US-202217750947-A
Country	US
Kind code	A1
Filing date	May 23, 2022
Priority date	May 26, 2021
Publication date	Dec 8, 2022
Grant date	—

Abstract

To determine an imaging quality of an optical system when illuminated by illumination light within a pupil to be measured of the optical system and/or to qualify the phase effect of a test structure, a test structure that is periodic in at least one dimension is initially arranged in an object plane of the optical system. An initial illumination angle distribution for illuminating the test structure with an initial pupil region, whose area is less than 10% of a total pupil area, is specified and the test structure is illuminated thereby in different distance positions relative to the object plane. In this way, an initial measured aerial image of the test structure is determined. Specifying the illumination distribution, illuminating and determining the aerial image are then repeated for a further illumination angle distribution and an imaging contribution of the optical system is determined from a comparison of the measured aerial images, the imaging quality parameter to be determined and/or a complex-valued diffraction spectrum of the test structure being determined from said imaging contribution. A metrology system for carrying out the method comprises a holder for the test structure, an illumination optical unit, a specification device for specifying the illumination angle distributions, the optical system to be examined in respect of its imaging quality, and a spatially resolving detection device for determining aerial images. This yields an improved imaging quality determination method.

First claim

What is claimed is:

1 . A method for determining an imaging quality of an optical system when illuminated by illumination light within a pupil to be measured of the optical system and/or for qualifying the phase effect of a test structure, including the following steps:
arranging a test structure that is periodic in at least one dimension (x; x, y) in an object plane of the optical system, specifying an initial illumination angle distribution ( k 0 ) for illuminating the test structure with the illumination light, represented by a contiguous, fully illuminated initial pupil region, the area of which is less than 10% of a total pupil area of the pupil, illuminating the test structure with the specified initial illumination angle distribution at different distance positions (z) of the test structure relative to the object plane, measuring an intensity of the illumination light in an image plane of the optical system using a spatially resolving detection device for the purposes of determining an initial measured aerial image (I( x , z, k 0 ) of the test structure, the illumination light having been guided by the optical system when imaging the test structure in each distance position (z), specifying a further illumination angle distribution ( k −1 , k +1 ) for illuminating the test structure with the illumination light, represented by a contiguous, fully illuminated further pupil region, the area of which is less than 10% of a total pupil area of the pupil, with the further pupil region not overlapping with the initial pupil region, illuminating the test structure with the specified further illumination angle distribution ( k −1 , k +1 ) at different distance positions (z) of the test structure relative to the object plane, measuring an intensity of the illumination light in the image plane of the optical system using the spatially resolving detection device for the purposes of determining a further measured aerial image (I( x , z, k −1 ), I( x , z, k +1 )) of the test structure, the illumination light having been guided by the optical system when imaging the test structure in each distance position (z), determining an imaging contribution of the optical system from a comparison of the measured aerial images, determining at least one imaging quality parameter from the measured imaging contribution, and/or determining a complex-valued diffraction spectrum of the test structure from the measured imaging contribution.

2 . The method of claim 1 , wherein the pupil has an at least approximately circular or elliptical edge, the pupil region representing the respective illumination angle distribution being able to be at least approximated by a circular or elliptical region with a radius that is no more than 30% of a radius of the pupil.

3 . The method of claim 1 , wherein the steps of “specifying a further illumination angle distribution,” “illuminating the test structure with the specified further illumination angle distribution” and “measuring an intensity” are repeated at least once.

4 . The method of claim 1 , wherein a measured spectrum (S) is measured within the scope of measuring the intensity and measured as a diffraction spectrum (M) of the periodic test structure guided through the optical system.

5 . The method of claim 4 , wherein a pure displacement of the test structure diffraction spectrum (M) in the pupil is included in the determination of the imaging contribution at the various illumination angle distributions ( k ).

6 . The method of claim 4 , wherein both of the diffraction spectrum (M) of the periodic test structure and the transfer function (T) of the optical system are included in the measured spectrum (S), the determination of the imaging contribution including the assumption that the transfer function (T) is constant for each illumination direction within the respectively specified illumination angle distribution ( k ).

7 . The method of claim 4 , wherein a reconstruction of the measured spectrum (S) is included in the determination of the imaging contribution.

8 . The method of claim 7 , wherein a difference between a measured aerial image (I meas ( x ,z, k )) and an aerial image (I( x ,z, k )) that depends on the measured spectrum (S) to be reconstructed is minimized during the reconstruction of the measured spectrum (S).

9 . The method of claim 1 , wherein a transfer function (T) of the optical system is reconstructed in amplitude and phase when determining the imaging contribution.

10 . The method of claim 1 , wherein a center of the further pupil region is spaced apart from a center of the initial pupil region by exactly one order of diffraction of a diffraction spectrum of the test structure.

11 . The method of claim 1 , wherein one of the pupil regions is located in the center of the pupil.

12 . The method of claim 1 , wherein the respective illumination angle distribution ( k ) is specified by positioning a stop in an illumination beam path in front of the optical system.

13 . A metrology system for carrying out the method of claim 1 , comprising
a holder for the test structure, an illumination optical unit for guiding illumination light to an object plane specified by the holder, a specification device for specifying the illumination angle distributions ( k ), the optical system to be examined in respect of its imaging quality, and a spatially resolving detection device for measuring the intensity of the illumination light in the image plane.

14 . The metrology system of claim 13 , wherein the specification device is embodied as a stop that is displaceable in driven fashion and is located in an illumination light beam path in front of the object plane.

15 . The metrology system of claim 13 , comprising a light source for the illumination light.

16 . The metrology system of claim 13 , wherein the pupil has an at least approximately circular or elliptical edge, the pupil region representing the respective illumination angle distribution being able to be at least approximated by a circular or elliptical region with a radius that is no more than 30% of a radius of the pupil.

17 . The metrology system of claim 13 , wherein the metrology system is configured to repeat the steps of “specifying a further illumination angle distribution,” “illuminating the test structure with the specified further illumination angle distribution” and “measuring an intensity” at least once.

18 . The metrology system of claim 13 , wherein the metrology system is configured to measure a measured spectrum (S) within the scope of measuring the intensity and measured as a diffraction spectrum (M) of the periodic test structure guided through the optical system.

19 . A metrology system, comprising
a holder configured to hold a test structure that is periodic in at least one dimension in an object plane of the optical system; an illumination optical unit configured to guide illumination light to the object plane specified by the holder; a specification device configured to specify a plurality of illumination angle distributions during different time periods; an optical system to be examined in respect of its imaging quality; a spatially resolving detection device configured to measure an intensity of the illumination light in an image plane of the optical system; a storage device storing instructions; at least one data processor configured to execute the instructions to implement a process comprising:
controlling the specification device to specify the plurality of illumi

Assignees

• Zeiss Carl Smt Gmbh

Inventors

• Koch Markus
• Capelli Renzo
• Gwosch Klaus
• Simakov Dmitry

Classifications

• G01M11/0207 Primary

  Details of measuring devices · CPC title

• G01M11/0264 Primary

  by using targets or reference patterns · CPC title

• G03F7/705

  Modelling or simulating from physical phenomena up to complete wafer processes or whole workflow in wafer productions · CPC title

• G01M11/02 Primary

  Testing optical properties · CPC title

• G03F1/84

  Inspecting · CPC title