US Patent 11675276 Metrology apparatus and photonic crystal fiber

A metrology apparatus for determining a parameter of interest of a structure formed by a lithographic process on a substrate, the metrology apparatus comprising: an illuminator for illuminating the structure; a lens for collecting at least a portion of radiation diffracted from the structure; and an image sensor for receiving and obtaining a recording of the collected diffracted radiation; wherein the illuminator comprises at least one optical fiber for illuminating the structure directly.