Method of Measuring a Parameter of Interest, Device Manufacturing Method, Metrology Apparatus, and Lithographic System

A method comprising:

• a first detecting or estimating of a reference property of radiation at a first wavelength scattered from a first sub-target of a target structure, the first sub-target comprising a first bias;
• a second detecting or estimating of the reference property of radiation at a second wavelength scattered from a second sub-target of the target structure, the second sub-target comprising a second bias different than the first bias, and the first wavelength being different from the second wavelength;
• and
• determining a parameter of interest based on the first and second detecting or estimating.

A device manufacturing method, comprising:

• forming structures on a substrate using a manufacturing sequence including at least one lithography step, the structures comprising a target structure;
• measuring a parameter of interest of the target structure, the measuring comprising:
• a first detecting or estimating of a reference property of radiation at a first wavelength scattered from a first sub-target of the target structure, the first sub-target comprising a first bias;
• a second detecting or estimating of the reference property of radiation at a second wavelength scattered from a second sub-target of the target structure, the second sub-target comprising a second bias different than the first bias, and the first wavelength being different from the second wavelength;
• and
• determining a parameter of interest based on the first and second detecting or estimating.

A metrology apparatus for measuring a parameter of interest of a target structure formed on a substrate, the apparatus comprising:

• a processor configured to:
• perform a first detecting or estimating of a reference property of radiation at a first wavelength scattered from a first sub-target of the target structure, the first sub-target comprising a first bias;
• perform a second detecting or estimating of the reference property of radiation at a second wavelength scattered from a second sub-target of the target structure, the second sub-target comprising a second bias different than the first bias, and the first wavelength being different from the second wavelength;
• and
• determine a parameter of interest based on the first and second detecting or estimating.

A lithographic system comprising:

• a lithographic apparatus configured to define structures to be formed on a substrate using a manufacturing sequence including at least one lithography step, the structures comprising a target structure;
• and
• a metrology apparatus for measuring a parameter of interest of a target structure formed on a substrate, the metrology apparatus comprising a processor configured to:
• perform a first detecting or estimating of a reference property of radiation at a first wavelength scattered from a first sub-target of the target structure, the first sub-target comprising a first bias;
• perform a second detecting or estimating of the reference property of radiation at a second wavelength scattered from a second sub-target of the target structure, the second sub-target comprising a second bias different than the first bias, and the first wavelength being different from the second wavelength;
• and
• determine a parameter of interest based on the first and second detecting or estimating.