# US 12,007,590 B2 · Two-dimensional diffraction grating > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,007,590 B2 - Document ID: US12007590B2 - Status: Granted - Kind: B2 - Application number: 16/965,172 - Filed: 2019-01-04 - Published: 2020-11-19 - Granted: 2024-06-11 - Earliest claimed: 2018-01-31 - Assignees: ASML Netherlands B.V. - Applicants: ASML Netherlands B.V. - Inventors: Pieter Cristiaan De Groot; Johannes Jacobus Matheus Baselmans; Derick Yun Chek Chong; Yassin Chowdhury - Web page: https://patentgrep.com/patent/US12007590B2 ## CPC - G02B 5/1819: {Plural gratings positioned on the same surface, e.g. array of gratings (plural diffractive elements positioned sequentially along the optical path G02B27/4272)} - G01M 11/0242: {by measuring geometrical properties or aberrations} - G01M 11/0271: {by using interferometric methods} - G02B 5/005: {Diaphragms (for cameras G03B9/02)} - G02B 27/0012: {Optical design, e.g. procedures, algorithms, optimisation routines} - G02B 27/4233: {having a diffractive element [DOE] contributing to a non-imaging application (diffusers having a diffractive element G02B5/0252; filters having a diffractive element G02B5/203; systems for controlling the direction of light having diffractive elements G02B26/0808; scanning systems having diffractive elements G02B26/106; beam shaping systems using diffractive optical elements G02B27/0944; beam splitting or combining systems operating by diffraction G02B27/1086)} - G03F 7/706: {Aberration measurement} - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - G01M: TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR - 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 A two-dimensional diffraction grating for a phase-stepping measurement system for determining an aberration map for a projection system comprises a substrate provided with a square array of through-apertures, wherein the diffraction grating is self-supporting. It will be appreciated that for a substrate provided with a square array of through-apertures to be self-supporting at least some substrate material is provided between each through-aperture and the adjacent through apertures. A method of designing a two-dimensional diffraction grating for a phase-stepping measurement system for determining an aberration map for a projection system comprises: selecting a general geometry for the two-dimensional diffraction grating, the general geometry having at least one parameter; and selecting values for the least one parameter that result in a grating efficiency map for the two-dimensional diffraction grating so as to control the contributions to a first harmonic of a phase stepping signal. ## Claims ### Claim 1 A two-dimensional diffraction grating for a phase-stepping measurement system for determining an aberration map for a projection system, the diffraction grating comprising: a substrate provided with a square array of through-apertures having a checkerboard pattern, the substrate comprising: a support layer; and a radiation absorbing layer, wherein the diffraction grating is transmissive, wherein the radiation absorbing layer is separate from the support layer, wherein the square array of through-apertures extend through both the support layer and the radiation absorbing layer, wherein the square array of through-apertures are non-regular octagonal and the square array of through-apertures are formed from a square having truncated corners, such that a connecting portion is formed between each two adjacent apertures, and wherein the connecting portion has at least two parallel sides. ### Claim 2 (depends on 1) The two-dimensional diffraction grating of claim 1, wherein a geometry of the two-dimensional diffraction grating is arranged to result in a grating efficiency map that reduces a number of contributions above a threshold to a harmonic of a phase stepping signal in response to the two-dimensional diffraction grating being used with a first patterned region that comprises a one-dimensional diffraction grating with a 50% duty cycle or a two-dimensional checkerboard diffraction grating with a 50% duty cycle. ### Claim 3 (depends on 1) The two-dimensional diffraction grating of claim 1, wherein: a geometry of the two-dimensional diffraction grating is arranged to result in a grating efficiency map that suppresses grating efficiencies of the (n, m)th diffraction orders, where either n or m is a non-zero even number; the square array of through-apertures are square apertures having a length that is half the distance between centers of adjacent through-apertures; and the sides of the square apertures are parallel to the axes of the square array of through-apertures. ### Claim 4 (depends on 1) The two-dimensional diffraction grating of claim 1, wherein a geometry of the two-dimensional diffraction grating is arranged to result in a grating efficiency map that suppresses grating efficiencies of the (n, m)th diffraction orders wherein n±m is an even number except the (0, 0)th diffraction order. ### Claim 5 (depends on 4) The two-dimensional diffraction grating of claim 4, wherein the square is orientated at 45° to the axes of the square array of through-apertures and has a diagonal dimension that matches a distance between the centers of adjacent through-apertures, and wherein the connecting portion of the substrate between each pair of adjacent through apertures is generally rectangular. ### Claim 6 (depends on 5) The two-dimensional diffraction grating of claim 5, wherein a width of the generally rectangular connecting portion of the substrate between each pair of adjacent through apertures is approximately 10% of the distance between centers of adjacent through-apertures. ### Claim 7 (depends on 1) The two-dimensional diffraction grating of claim 1, wherein a geometry of the two-dimensional diffraction grating is arranged to result in a grating efficiency map that suppresses a grating efficiency of one or more diffraction orders, the one or more diffraction orders being the (n, m)th diffraction orders wherein n±m is an even number. ### Claim 8 (depends on 7) The two-dimensional diffraction grating of claim 7, wherein the geometry of the two-dimensional diffraction grating is arranged to suppress (±2, 0) and (0,±2) diffraction orders. ### Claim 9 (depends on 7) The two-dimensional diffraction grating of claim 7, wherein the geometry of the two-dimensional diffraction grating is arranged to suppress (±1,±1) diffraction orders. ### Claim 10 (depends on 1) The two-dimensional diffraction grating of claim 1, wherein a width of the connecting portion is from about 5% to about 15% of a distance between centers of two adjacent apertures. ### Claim 11 A method of manufacturing a two-dimensional diffraction grating for a phase-stepping measurement system for determining an aberration map for a projection system, the method comprising: selecting a geometry for the two-dimensional diffraction grating, the geometry having at least one parameter; and selecting values for the at least one parameter that result in a grating efficiency map for the two-dimensional diffraction grating so as to control contributions to a harmonic of a phase stepping signal, wherein the two-dimensional diffraction grating is transmissive, wherein the two-dimensional diffraction grating comprises a substrate provided with a square array of through-apertures having a checkerboard pattern, wherein the substrate comprises a support layer and a radiation absorbing layer, wherein the support layer is separate from the radiation absorbing layer, wherein the square array of through-apertures extend through both the support layer and the radiation absorbing layer, wherein the square array of through-apertures are non-regular octagonal and the square array of through-apertures are formed from a square having truncated corners, such that a connecting portion is formed between each two adjacent apertures, and wherein the connecting portion has at least two parallel sides. ### Claim 12 (depends on 11) The method of claim 11, wherein the selection of values for the least one parameter that result in the grating efficiency map for the two-dimensional diffraction grating so as to control the contributions to a harmonic of a phase stepping signal results from the two-dimensional diffraction grating being used with a first patterned region that comprises a one-dimensional diffraction grating with a 50% duty cycle or a two-dimensional checkerboard diffraction grating with a 50% duty cycle. ### Claim 13 (depends on 11) The method of claim 11, wherein: the selecting values for the least one parameter comprises selecting values for the least one parameter that minimizes a grating efficiency of one or more diffraction orders, the one or more diffraction orders being the (n, m)th diffraction orders, wherein n±m is an even number, and the step of selecting values for the least one parameter involves selecting values for the least one parameter that minimizes a grating efficiency of (±2, 0) and (0,±2) diffraction orders. ### Claim 14 (depends on 11) The method of claim 11, wherein the selecting values for the least one parameter comprises selecting values for the least one parameter that minimizes a grating efficiency of (±1, ±1) diffraction orders. ### Claim 15 (depends on 11) The method of claim 11, further comprising: fabricating the two-dimensional diffraction grating using the selected values. ### Claim 16 A two-dimensional diffraction grating, comprising: a geometry configured to be selected to have at least one parameter, such that the least one parameter is configured to result in a grating efficiency map for the two-dimensional diffraction grating so as to control contributions to a harmonic of a phase stepping signal, wherein the two-dimensional diffraction grating is transmissive, wherein the two-dimensional diffraction grating comprises a substrate provided with a square array of through-apertures, wherein the substrate comprises a support layer and a radiation absorbing layer, wherein the support layer is separate from the radiation absorbing layer, wherein the square array of through-apertures extend through both the support layer and the radiation absorbing layer, and the square array of through-apertures are non-regular octagonal, and wherein each through-aperture is formed from a square having a diagonal dimension that matches a distance between centers of two adjacent apertures.