US Patent 10895452 Metrology apparatus

A metrology apparatus for determining a characteristic of interest of a structure on a substrate, the apparatus comprising: a radiation source for generating illumination radiation; at least two illumination branches for illuminating the structure on the substrate, the illumination branches being configured to illuminate the structure from different angles; and a radiation switch configured to receive the illumination radiation and transfer at least part of the radiation to a selectable one of the at least two illumination branches.