Assemblies and methods for two-channel measurements

Abstract

Assembly for determining a characteristic of a structure on a substrate, comprising a radiation illumination dipole having first and second sources that are angularly offset to a transverse direction in an illumination pupil plane. The first and second sources irradiate a structure having a periodically repeating pattern along a transverse. A multi-part wedge is located in an exit pupil of the assembly, configured to receive from the structure: a lower radiation order and a higher radiation order of diffracted radiation of the first source on a first part of the multi-part wedge, and a lower radiation order and a higher radiation order of diffracted radiation of the second source on a second part of the multi-part wedge. A detector receives a first and second spatially separated images formed from first and second source radiation incident on the first and second parts of the wedge, respectively.

Images