Method of determining information about a patterning process, method of reducing error in measurement data, method of calibrating a metrology process, method of selecting metrology targets

A method comprising:

• obtaining measurement data from a metrology process applied to each of a plurality of metrology targets on a substrate, wherein the measurement data for each metrology target comprises at least a first contribution and a second contribution, the first contribution being from a parameter of interest of a patterning process used to form the metrology target, the second contribution being from an error in the metrology process used to measure the metrology target;
• using the obtained measurement data from all of the plurality of metrology targets to obtain information about an error in the metrology process;
• and
• using the obtained information to reduce error in the measurement data.

A method comprising:

• obtaining measurement data from a metrology process applied to each of a plurality of metrology targets on a substrate, wherein the measurement data for each metrology target comprises at least a first contribution and a second contribution, the first contribution being from a parameter of interest of a patterning process used to form the metrology target, the second contribution being from an error in the metrology process used to measure the metrology target;
• using the obtained measurement data from all of the plurality of metrology targets to obtain information about an error in the metrology process;
• and
• using the obtained information to calibrate the metrology process to reduce error in measurement data produced by the metrology process.