Method of Measuring a Structure, Inspection Apparatus, Lithographic System and Device Manufacturing Method

A method, comprising:

• measuring a property of a plurality of structures formed by a lithographic process on one or more substrates, the measuring of the property of each structure is derived at least partly from radiation collected after being scattered by the structure under a given set of illumination conditions,
• influencing accuracy of the measuring for different ones of the structures, for a given set of illumination conditions, based on process variations across the substrate and/or between substrates;
• and
• performing the measuring using radiation collected under two or more variants of the illumination conditions, wherein for different ones of the structures the measurement of the property is derived using radiation collected under a different selection or combination of the variants.

An inspection apparatus for measuring a property of a plurality of structures formed by a lithographic process on one or more substrates, the apparatus comprising:

• an illumination optical system,
• an collection optical system;
• and
• a processing system arranged to derive a measurement of the property of each structure at least partly from radiation collected by the collection optical system after being scattered by the structure under one or more sets of illumination conditions established by the illumination optical system,
• wherein, for a given set of illumination conditions, accuracy of the measurement for different ones of the structures is influenced by process variations across the substrate and/or between substrates,
• wherein the illumination system and collection system are arranged to collect radiation scattered by a plurality of structures under two or more variants of the illumination conditions, and
• wherein the processing system is arranged to derive the measurement of the property using radiation collected under a different selection or combination of the variants for different ones of the structures.

A computer program product comprising machine readable instructions for causing a programmable processing device to perform operations comprising:

• measuring a property of a plurality of structures formed by a lithographic process on one or more substrates, the measuring of the property of each structure is derived at least partly from radiation collected after being scattered by the structure under a given set of illumination conditions,
• influencing accuracy of the measuring for different ones of the structures, for a given set of illumination conditions, based on process variations across the substrate and/or between substrates;
• and
• performing the measuring using radiation collected under two or more variants of the illumination conditions, wherein for different ones of the structures the measurement of the property is derived using radiation collected under a different selection or combination of the variants

A lithographic system comprising:

• a lithographic apparatus comprising:
• an illumination system arranged to illuminate a pattern;
• a projection system arranged to project an image of the pattern onto a substrate;
• and
• an inspection apparatus for measuring a property of a plurality of structures formed by a lithographic process on one or more substrates, the inspection apparatus comprising:
• an illumination optical system,
• an collection optical system;
• and
• a processing system arranged to derive a measurement of the property of each structure at least partly from radiation collected by the collection optical system after being scattered by the structure under one or more sets of illumination conditions established by the illumination optical system,
• wherein, for a given set of illumination conditions, accuracy of the measurement for different ones of the structures is influenced by process variations across the substrate and/or between substrates,
• wherein the illumination system and collection system are arranged to collect radiation scattered by a plurality of structures under two or more variants of the illumination conditions, and
• wherein the processing system is arranged to derive the measurement of the property using radiation collected under a different selection or combination of the variants for different ones of the structures,
• wherein the lithographic apparatus is arranged to use the measurement results from the inspection apparatus in applying the pattern to further substrates.

A method of manufacturing devices, comprising:

• measuring a property of a plurality of structures formed by a lithographic process on one or more substrates, the measuring of the property of each structure is derived at least partly from radiation collected after being scattered by the structure under a given set of illumination conditions,
• influencing accuracy of the measuring for different ones of the structures, for a given set of illumination conditions, based on process variations across the substrate and/or between substrates;
• performing the measuring using radiation collected under two or more variants of the illumination conditions, wherein for different ones of the structures the measurement of the property is derived using radiation collected under a different selection or combination of the variants;
• and
• controlling the lithographic process for later substrates in accordance with the result of the measuring.