Method and apparatus for angular-resolved spectroscopic lithography characterization

A scatterometer, comprising:

• a lens configured to direct a radiation beam from a radiation source toward a pattern formed on a substrate;
• a first beam splitter configured to split the radiation beam into two polarized beam components;
• a detector located in a pupil plane of the lens and configured to detect an angle-resolved spectrum of the two polarized beam components reflected from a surface of the substrate;
• a second beam splitter;
• and
• a tilted mirror,
• wherein the second beam splitter and the tilted mirror are configured to direct a portion of the radiation beam for separate measurement by the detector.