Metrology method and apparatus, computer program and lithographic system

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.

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.

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.

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.