Method for operating a reflectometer

By determining polarization through reflectivity measurements in orthogonal reflection planes and using a layer model, the method addresses inaccuracies in EUV reflectometers, ensuring precise characterization of EUV mirrors and enhancing the optical properties of microlithographically projected exposure apparatuses.

DE102024207158B3Active Publication Date: 2025-07-31CARL ZEISS SMT GMBH
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Patent Information

Application Number
DE102024207158
Authority / Receiving Office
DE · DE
Patent Type
Patents
Current Assignee / Owner
Filing Date
2024-07-30
Publication Date
2025-07-31
Estimated Expiration
2044-07-30

AI Technical Summary

Technical Problem

EUV reflectometers face challenges in accurately determining the polarization of measurement radiation, leading to incorrect characterization of test objects like EUV mirrors, which affects the optical properties of microlithographically projected exposure apparatuses due to fluctuations and changes in the measurement process.

Method used

Determine the polarization of measurement radiation by measuring reflectivity in two orthogonal reflection planes and using a layer model to calculate polarization based on the difference between reflectivity maxima, ensuring accurate characterization of test objects.

Benefits of technology

This method enables reliable qualification of test objects by providing highly accurate polarization determination, improving the precision of manufacturing processes and optimizing the optical properties of systems like EUV mirrors and microlithographically projected exposure apparatuses.

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Abstract

The invention relates to a method for operating a reflectometer, wherein in the reflectometer (100) the reflectivity of a test object (103) is determined as a ratio between the intensity of a measuring beam (102) after reflection at the test object and the intensity of the measuring beam before reflection at the test object, wherein the method comprises the following steps: determining a first reflectivity maximum of the wavelength-dependent reflectivity of the test object in a first measuring geometry in which the reflection of the measuring beam at the test object takes place in a first reflection plane, determining a second reflectivity maximum of the wavelength-dependent reflectivity of the test object in a second measuring geometry in which the reflection of the measuring beam at the test object takes place in a second reflection plane,wherein the first measurement geometry and the second measurement geometry coincide with respect to the angle of incidence and point of incidence of the measurement beam incident on the test specimen, and wherein the second reflection plane is orthogonal to the first reflection plane, and determining the polarization of the measurement beam based on the difference between the first and second reflectivity maximum and a layer model.
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Claims

[1] Method for operating a reflectometer, wherein in the reflectometer (100) a determination of the reflectivity of a test object (103) is carried out as a ratio between the intensity of a measuring beam (102) after reflection at the test object (103) and the intensity of the measuring beam (102) before reflection at the test object (103), wherein the method comprises the following steps: - determining a first reflectivity maximum of the wavelength-dependent reflectivity of the test object (103) in a first measuring geometry in which the reflection of the measuring beam (102) on the test object (103) takes place in a first reflection plane; - determining a second reflectivity maximum of the wavelength-dependent reflectivity of the test object (103) in a second measuring geometry in which the reflection of the measuring beam (102) on the test object (103) takes place in a second reflection plane; - wherein the first measuring geometry and the second measuring geometry coincide with respect to the angle of incidence and point of incidence of the measuring beam (102) incident on the test object (103), and wherein the second reflection plane is orthogonal to the first reflection plane; and - Determining the polarization of the measuring beam (102) based on the difference between the first and second reflectivity maximum and a layer model. [2] Method according to claim 1, characterized by that the determination of the first reflectivity maximum and the determination of the second reflectivity maximum are each carried out on the basis of a reflectivity spectrum recorded by tuning the wavelength of the measuring beam (102). [3] Method according to claim 1 or 2, characterized bythat the determination of the first reflectivity maximum and the determination of the second reflectivity maximum are carried out repeatedly for different angles of incidence of the measuring beam (102) incident on the test piece (103). [4] Method according to one of claims 1 to 3, characterized by that the measuring beam (102) has a wavelength of less than 30 nm, in particular less than 15 nm. [5] Method according to one of the preceding claims, characterized by that the test piece (103) is a mirror, in particular for microlithography. [6] Reflectometer (100) for carrying out reflectivity measurements on a test specimen (103), characterized by that it is designed to carry out a method according to one of the preceding claims.

Citation Information

Patent Citations

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