# US 10,369,752 B2 · Metrology method and apparatus, computer program and lithographic system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,369,752 B2 - Document ID: US10369752B2 - Status: Granted - Kind: B2 - Application number: 15/138,903 - Filed: 2016-04-26 - Published: 2016-11-10 - Granted: 2019-08-06 - Earliest claimed: 2015-05-07 - Assignees: ASML Netherlands B.V. - Applicants: ASML Netherlands B.V. - Inventors: Seyed Iman Mossavat; Adriaan Johan Van Leest - Web page: https://patentgrep.com/patent/US10369752B2 ## CPC - B29C 64/386: Data acquisition or data processing for additive manufacturing - G03F 7/705: {Modelling or simulating from physical phenomena up to complete wafer processes or whole workflow in wafer productions} - G03F 7/70625: {Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness} - G05B 19/4099: Surface or curve machining, making three-dimensional [3D] objects, e.g. desktop manufacturing - B33Y 50/02: for controlling or regulating additive manufacturing processes - G05B 2219/35134: 3-D cad-cam - G05B 2219/49007: Making, forming 3-D object, model, surface - B29C: SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING (making preforms B29B11/00; making laminated products by combining previously unconnected layers which become one product whose layers will remain together B32B37/00 - B32B41/00) - 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) - G05B: CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS (systems for controlling or regulating non-electric variables G05D; systems for regulating electric or magnetic variables G05F; control devices or systems insofar as characterised by mechanical features only G05G) - B33Y: ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING ## Abstract Disclosed are a method, computer program and associated apparatuses for metrology. The method includes acquiring inspection data comprising a plurality of inspection data elements, each inspection data element having been obtained by inspection of a corresponding target structure formed using a lithographic process; and performing an unsupervised cluster analysis on said inspection data, thereby partitioning said inspection data into a plurality of clusters in accordance with a metric. In an embodiment, a cluster representative can be identified for each cluster. The cluster representative may be reconstructed and the reconstruction used to approximate the other members of the cluster. ## Claims ### Claim 1 A method of metrology comprising: acquiring inspection data, the inspection data comprising a plurality of inspection data elements, each inspection data element having been obtained by inspection of a corresponding target structure formed using a lithographic process in a lithographic system; performing an unsupervised cluster analysis on the inspection data, thereby partitioning the inspection data into a plurality of clusters in accordance with a metric; determining a representative inspection data element for each of the plurality of clusters, each representative inspection data element corresponding to a representative target structure formed using the lithographic process; performing a reconstruction operation to obtain at least one reconstructed parameter value from each representative inspection data element, the at least one reconstructed parameter value comprising a value for at least one parameter of the corresponding representative target structure formed using the lithographic process; and performing a targeted reconstruction operation of each target structure, other than the representative target structures, based upon the at least one reconstructed parameter value of at least one of the representative target structures, wherein the targeted reconstruction operation for each target structure is based upon the at least one reconstructed parameter value for the representative target structure of the cluster of which that target structure is a member. ### Claim 2 (depends on 1) The method as claimed in claim 1, wherein: the inspection data comprises measured intensities within spectra or images, and the spectra or images comprise diffraction spectra or images obtained by the inspection using a scatterometer. ### Claim 3 (depends on 1) The method as claimed in claim 1, wherein the inspection data comprises values for at least one parameter of the corresponding target structure as determined by a subsequent reconstruction operation on the inspection data. ### Claim 4 (depends on 1) The method as claimed in claim 1, wherein the partitioning of the inspection data is performed in accordance with a relative distance, as defined by the metric, between each inspection data element and a cluster center of each cluster. ### Claim 5 (depends on 1) The method as claimed in claim 1, wherein the partitioning of the inspection data is performed in accordance with one or more statistical distribution models, such that each cluster is defined as comprising the inspection data elements belonging to the same distribution. ### Claim 6 (depends on 1) The method as claimed in claim 1, wherein each representative inspection data element is a closest to an average inspection data element, in terms of the metric, for its corresponding cluster. ### Claim 7 (depends on 1) The method as claimed in claim 1, wherein the at least one reconstructed parameter value for each representative target structure is used to derive a nominal value for at least one model parameter in subsequent reconstruction operations. ### Claim 8 (depends on 1) The method as claimed in claim 1, wherein the targeted reconstruction operation for each target is further based upon a weighted average of reconstructed parameter values for all, or a subset of, the representative target structures. ### Claim 9 (depends on 1) The method as claimed in claim 1, wherein a number of clusters is automatically learned. ### Claim 10 (depends on 9) The method as claimed in claim 9, wherein the number of clusters is automatically learned by: performing the clustering analysis multiple times, each time partitioning the inspection data into n clusters, wherein n is chosen to be between 3 and 8 and is increased each time a cluster analysis is performed, determining an average within cluster distance according to the metric for each cluster analysis, and selecting the cluster analysis for which the average within cluster distance meets a threshold criterion. ### Claim 11 (depends on 1) The method as claimed in claim 1, wherein the acquiring inspection data comprises: inspecting the target structures by illuminating each one of the target structures with measurement radiation and detecting the radiation scattered by each one of the target structures. ### Claim 12 A metrology apparatus comprising: a support configured to support a substrate having a plurality of target structures thereon, the plurality of target structures formed using a lithographic process in a lithographic system; an optical system used in inspection of the plurality of target structures; and a processor configured to: acquire inspection data, the inspection data comprising a plurality of inspection data elements, each inspection data element having been obtained by the inspection of a corresponding target structure; perform an unsupervised cluster analysis on the inspection data, thereby partitioning the inspection data into a plurality of clusters in accordance with a metric; determine a representative inspection data element for each of the plurality of clusters, each representative inspection data element corresponding to a representative target structure formed using the lithographic process; perform a reconstruction operation to obtain at least one reconstructed parameter value from each representative inspection data element, the at least one reconstructed parameter value comprising a value for at least one parameter of the corresponding representative target structure formed using the lithographic process; and for each of the plurality of clusters, perform a second reconstruction operation of each target structure, other than the corresponding representative target structure, based at least on the at least one reconstructed parameter value of the corresponding representative target structure, wherein the targeted reconstruction operation for each target is based upon a weighted average of reconstructed parameter values for all, or a subset of, the representative target structures. ### Claim 13 A lithographic system comprising: a lithographic apparatus comprising: an illumination optical system configured to illuminate a pattern; and a projection optical system configured to project an image of the pattern onto a substrate; and a metrology apparatus configured to: acquire inspection data, the inspection data comprising a plurality of inspection data elements, each inspection data element having been obtained by inspection of a corresponding target structure formed using the lithographic apparatus; perform an unsupervised cluster analysis on the inspection data, thereby partitioning the inspection data into a plurality of clusters in accordance with a metric; determine a representative inspection data element for each of the plurality of clusters, each representative inspection data element corresponding to a representative target structure formed using the lithographic apparatus; perform a reconstruction operation to obtain at least one reconstructed parameter value from each representative inspection data element, the at least one reconstructed parameter value comprising a value for at least one parameter of the corresponding representative target structure formed using the lithographic apparatus; and perform a targeted reconstruction operation of each target structure, other than the representative target structures, based upon the at least one reconstructed parameter value of at least one of the representative target structures, wherein the targeted reconstruction operation for each target structure is based upon the at least one reconstructed parameter value for the representative target structure of the cluster of which that target structure is a member. ### Claim 14 A computer program comprising processor readable instructions which, when run on a suitable processor controlled apparatus, cause the processor controlled apparatus to perform a method comprising: acquiring inspection data, the inspection data comprising a plurality of inspection data elements, each inspection data element having been obtained by inspection of a corresponding target structure formed using a lithographic process in a lithographic system; performing an unsupervised cluster analysis on the inspection data, thereby partitioning the inspection data into a plurality of clusters in accordance with a metric; determining a representative inspection data element for each of the plurality of clusters, each representative inspection data element corresponding to a representative target structure formed using the lithographic process; performing a reconstruction operation to obtain at least one reconstructed parameter value from each representative inspection data element, the at least one reconstructed parameter value comprising a value for at least one parameter of the corresponding representative target structure formed using the lithographic process; and performing a targeted reconstruction operation of each target structure, other than the representative target structures, based upon the at least one reconstructed parameter value of at least one of the representative target structures, wherein the targeted reconstruction operation for each target structure is based upon the at least one reconstructed parameter value for the representative target structure of the cluster of which that target structure is a member. ### Claim 15 A computer program carrier comprising a computer program comprising processor readable instructions which, when run on a suitable processor controlled apparatus, cause the processor controlled apparatus to perform a method comprising: acquiring inspection data, the inspection data comprising a plurality of inspection data elements, each inspection data element having been obtained by inspection of a corresponding target structure formed using a lithographic process in a lithographic system; performing an unsupervised cluster analysis on the inspection data, thereby partitioning the inspection data into a plurality of clusters in accordance with a metric; determining a representative inspection data element for each of the plurality of clusters, each representative inspection data element corresponding to a representative target structure formed using the lithographic process; performing a reconstruction operation to obtain at least one reconstructed parameter value from each representative inspection data element, the at least one reconstructed parameter value comprising a value for at least one parameter of the corresponding representative target structure formed using the lithographic process; and performing a targeted reconstruction operation of each target structure, other than the representative target structures, based upon the at least one reconstructed parameter value of at least one of the representative target structures, wherein the targeted reconstruction operation for each target is based upon a weighted average of reconstructed parameter values for all, or a subset of, the representative target structures.