# US 11,079,338 B2 · Method for detecting a structure of a lithography mask and device for carrying out the method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,079,338 B2 - Document ID: US11079338B2 - Status: Granted - Kind: B2 - Application number: 16/451,203 - Filed: 2019-06-25 - Published: 2019-12-26 - Granted: 2021-08-03 - Earliest claimed: 2018-06-25 - Assignees: Carl Zeiss SMT GmbH - Applicants: Carl Zeiss SMT GmbH - Inventors: Ulrich Matejka; Thomas Scheruebl; Markus Koch; Christoph Husemann; Lars Stoppe; Beat Marco Mout - Web page: https://patentgrep.com/patent/US11079338B2 ## CPC - G01N 21/956: Inspecting patterns on the surface of objects {(contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)} - G01B 9/02083: {characterised by particular signal processing and presentation} - G01N 21/33: using ultraviolet light (G01N21/39 takes precedence) - G03F 1/84: Inspecting - G01N 2021/95676: {Masks, reticles, shadow masks} - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) - G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS - G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G) ## Abstract In detecting the structure of a lithography mask, a portion of the lithography mask is firstly illuminated with illumination light of an at least partially coherent light source in the at least one preferred illumination direction. A diffraction image of the illuminated portion is then recorded by spatially resolved detection of a diffraction intensity of the illumination light diffracted from the illuminated portion in a detection plane. The steps of “illuminating” and “recording the diffraction image” are then carried out for further portions of the lithography mask. Between at least two portions of the lithography mask that are thereby detected, there is in each case an overlap region whose surface extent measures at least 5% or more of the smaller of the two portions of the lithography mask. The repetition takes place until the detected portions of the lithography mask completely cover a region of the lithography mask to be detected. The structure of the lithography mask is calculated from the recorded diffraction images of the illuminated portions. A device for carrying out the structure detection method is also specified, which comprises a light source, a spatially-resolving detector and a mask holder. This results in a method and a device for detecting the structure of a lithography mask, in which the demands placed on an optical unit arranged downstream in the beam path from the illumination light of the lithography mask are reduced. ## Claims ### Claim 1 A method for detecting a structure of a lithography mask, comprising the following steps: illuminating a portion of the lithography mask with illumination light of an at least partially coherent light source in at least one predetermined illumination direction, recording a diffraction image of the illuminated portion by spatially resolved detection of a diffraction intensity of the illumination light diffracted from the illuminated portion in a detection plane, repeating the “illuminating” and “recording” steps for further portions of the lithography mask, wherein between at least two portions of the lithography mask that are thereby detected there is in each case an overlap region whose surface extent measures at least 5% of the smaller of the two portions, until the detected portions completely cover a region of the lithography mask to be detected, and calculating the structure of the lithography mask from the recorded diffraction images of the illuminated portions, wherein the illuminated portion is illuminated with several predetermined illumination directions, wherein the diffraction image of the portion illuminated with these several predetermined illumination directions is in each case recorded. ### Claim 2 (depends on 1) The method of claim 1, wherein the calculation of the structure of the lithography mask takes place using a method of coherent diffraction imaging (CDI) or ptychography. ### Claim 3 (depends on 2) The method of claim 2, comprising using a non-Hopkins approximation. ### Claim 4 (depends on 2) The method of claim 2, comprising using a Fourier transformation in the calculation of the structure of the lithography mask from the recorded diffraction images. ### Claim 5 (depends on 2) The method of claim 2, comprising taking into consideration a degree of coherence of the light source in the calculation of the structure of the lithography mask from the recorded diffraction images. ### Claim 6 (depends on 2) The method of claim 2, comprising using measured positions of the illuminated portions on the lithography mask in the calculation of the structure of the lithography mask from the recorded diffraction images. ### Claim 7 (depends on 2) A device for carrying out a method of claim 2, the device comprising: a light source for providing the illumination light; a spatially resolving detector, arranged in the detection plane, for detecting a diffraction intensity in the recording of the diffraction image; and a mask holder which is displaceable in order to change between the portions of the lithography mask that are to be illuminated. ### Claim 8 (depends on 1) The method of claim 1, comprising the use of a non-Hopkins approximation. ### Claim 9 (depends on 1) The method of claim 1, wherein a Fourier transformation is used in the calculation of the structure of the lithography mask from the recorded diffraction images. ### Claim 10 (depends on 9) The method of claim 9, wherein an iterative Fourier transformation algorithm (IFTA) is used in the calculation of the structure of the lithography mask from the recorded diffraction images. ### Claim 11 (depends on 1) The method of claim 1, wherein a degree of coherence of the light source is taken into consideration in the calculation of the structure of the lithography mask from the recorded diffraction images. ### Claim 12 (depends on 1) The method of claim 1, wherein measured positions of the illuminated portions on the lithography mask are used in the calculation. ### Claim 13 (depends on 1) The method of claim 1, wherein the measurement takes place through a pellicle. ### Claim 14 (depends on 1) A device for carrying out a method of claim 1, the device comprising: a light source for providing the illumination light, a spatially resolving detector, arranged in the detection plane, for detecting a diffraction intensity in the recording of the diffraction image, and a mask holder which is displaceable in order to change between the portions of the lithography mask that are to be illuminated. ### Claim 15 (depends on 14) The device of claim 14, comprising at least one coupling mirror for coupling the illumination light onto the illuminated portion of a reflecting lithography mask, wherein the detector is arranged such that it receives the diffraction image of the illuminated portion in reflection. ### Claim 16 (depends on 15) The device of claim 15, wherein the illumination light in the beam path before the coupling mirror runs between an object plane and the detector. ### Claim 17 (depends on 15) The device of claim 15, wherein the coupling mirror is arranged in the beam path of the illumination light reflected by the illuminated portion. ### Claim 18 (depends on 14) The device of claim 14, wherein the illumination light, before impinging on the illuminated portion, is guided between portions of a detection surface of the detector. ### Claim 19 (depends on 14) The device of claim 14, wherein the mask holder is tiltable. ### Claim 20 (depends on 14) The device of claim 14, comprising a synchrotron-based light source or a high harmonic generation (HHG) light source. ### Claim 21 (depends on 14) The device of claim 14, comprising a stop positioned at an illumination pupil, wherein the stop is configured to provide multiple illumination directions arranged at an edge of the illumination pupil. ### Claim 22 (depends on 14) The device of claim 14, comprising a stop positioned at an illumination pupil, wherein the stop is configured to provide multiple illumination directions that are distributed in a central radius of the illumination pupil. ### Claim 23 (depends on 22) The device of claim 22, wherein the stop is configured to provide multiple illumination directions that are distributed in a first central radius of the illumination pupil, and illumination directions that are distributed in a second central radius of the illumination pupil. ### Claim 24 (depends on 14) The device of claim 14, comprising a stop positioned at an illumination pupil, wherein the stop is configured to provide at least four illumination directions that are distributed in a central radius of the illumination pupil. ### Claim 25 (depends on 14) The device of claim 14, comprising a stop positioned at an illumination pupil, wherein the stop is configured to provide at least eight illumination directions that are distributed in a central radius of the illumination pupil. ### Claim 26 (depends on 1) The method of claim 1 wherein the several predetermined illumination directions comprise illumination directions that are arranged at an edge of an illumination pupil. ### Claim 27 (depends on 1) The method of claim 1 wherein the several predetermined illumination directions comprise multiple illumination directions that are distributed in a central radius of an illumination pupil. ### Claim 28 (depends on 27) The method of claim 27, wherein the several predetermined illumination directions comprise illumination directions that are distributed in a first central radius of the illumination pupil, and illumination directions that are distributed in a second central radius of the illumination pupil. ### Claim 29 (depends on 1) The method of claim 1 wherein the several predetermined illumination directions comprise four illumination directions that are distributed in a central radius of an illumination pupil. ### Claim 30 (depends on 1) The method of claim 1 wherein the several predetermined illumination directions comprise eight illumination directions that are distributed in a central radius of an illumination pupil.