Metrology method and device for determining a complex-valued field

A computer program comprising program instructions operable to perform operations comprising:

• obtaining an amplitude profile of scattered radiation relating to a measurement of a structure on a substrate;
• obtaining a reference phase profile relating to a reference measurement of at least one reference structure on a reference substrate, the at least one reference structure being a different structure than the structure, and the at least one reference structure and the structure being nominally identical in terms of at least a plurality of key parameters;
• and
• determining a complex-valued field to describe the structure from the amplitude profile and the reference phase profile.

A lithographic cell comprising:

• a metrology device operable to perform measurements from which corrections are determined for a lithographic process and operable to perform the measurements and the corrections by:
• obtaining an amplitude profile of scattered radiation relating to a measurement of a structure on a substrate;
• obtaining a reference phase profile relating to a reference measurement of at least one reference structure on a reference substrate, the at least one reference structure being a different structure than the structure, and the at least one reference structure and the structure being nominally identical in terms of at least a plurality of key parameters;
• and
• determining a complex-valued field to describe the structure from the amplitude profile and the reference phase profile;
• and
• a lithographic apparatus operable to perform the lithographic process in accordance with the corrections.