OCD measurement of defocus and dose in EUV lithography

Critical dimension (CD) and geometry shape of the gratings play a key role in extreme ultraviolet (EUV) lithography to ensure the device performance. It is important to control the dose/defocus in the EUV photolithography under proper status to make sure the CD and shape meeting the fine and strict requirements. Through the OCD measurement, we build a relationship between the CD/shape and dose/defocus through a Focus-Exposure-Matrix (FEM) wafer, and eventually can measure the dose/defocus in a product wafer.