Method for filtering an image and associated metrology apparatus

A method for a metrology measurement on an area of a substrate comprising at least a portion of a target structure, the method comprising:

• receiving, at an image plane, radiation information representing at least a portion of both the target structure and non-target structure dark field diffraction radiation scattered by the area;
• converting the received radiation information in a pupil plane or Fourier domain;
• using one or more filters in the pupil plan or Fourier domain to remove or suppress at least one pair of opposing higher diffraction orders within at least a portion of radiation scattered by the area to generate image data;
• and
• using the image data to adjust a parameter of interest of a semiconductor process.

A metrology apparatus for a metrology measurement on an area of a substrate comprising at least a portion of a target structure, the metrology apparatus being configured to:

• receive, at an image plane, a radiation information representing at least a portion of both the target structure and non-target structure dark field diffraction radiation scattered by the area;
• convert the received radiation information in a pupil plane or Fourier domain;
• use a filter in the pupil plane of Fourier domain to remove or suppress at least a portion of the received radiation information that does not relate to radiation that has been scattered by the target structure to obtain a filtered radiation information for the metrology measurement, wherein characteristics of the filter are based on target information about the target structure;
• convert the filtered radiation information into image data;
• and
• use the image data to adjust a parameter of interest of a semiconductor process.