Method and apparatus for determining structure parameters of microstructures

An inspection apparatus comprising:

• a projection system configured to illuminate a first region of a target with a first beam of coherent radiation;
• a measurement system configured to measure a diffraction intensity pattern arising from the illumination of the first region;
• wherein the projection system is configured to illuminate a second region of the target, offset from and overlapping with the first region, with a second beam of coherent radiation and the measurement system is configured to measure a second diffraction intensity pattern arising from the illumination of the second region;
• and
• a processor configured to:
• retrieve phase information from the measured first and second diffraction intensity patterns;
• model the target using an estimated structure parameter to calculate a modeled diffraction intensity pattern;
• model the target using the estimated structure parameter to calculate modeled phase information;
• and
• determine the structure parameter of the target corresponding to the estimated structure parameter by comparing at least one of the first and second measured diffraction intensity patterns and the retrieved phase to the calculated modeled diffraction intensity pattern and the modeled phase information.

A non-transitory computer readable medium containing one or more sequences of machine-readable instructions, the instructions being adapted to cause one or more processors to perform an operation comprising:

• illuminating a first region of a target with a first beam of coherent radiation using a projection system;
• measuring a diffraction intensity pattern arising from the illumination of the first region;
• illuminating a second region of the target, offset from and overlapping with the first region, with a second beam of coherent radiation using the projection system;
• measuring a second diffraction intensity pattern arising from the illumination of the second region;
• retrieving phase information from the measured first and second diffraction intensity patterns;
• modeling the target using an estimated structure parameter to calculate a modeled diffraction intensity pattern;
• modeling the target using the estimated structure parameter to calculate modeled phase information;
• and
• determining the structure parameter of the target corresponding to the estimated structure parameter by comparing at least one of the first and second measured diffraction intensity patterns and the retrieved phase to the calculated modeled diffraction intensity pattern and the modeled phase information.