US Patent 11549806 Metrology apparatus

A metrology apparatus for determining a characteristic of interest of a structure on a substrate, the apparatus comprising: a radiation source configured to generate illumination radiation; at least two illumination branches comprising at least one optical fiber and configured to illuminate a structure on a substrate 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.