公开(公告)号：US20240385356A1

公开(公告)日：2024-11-21

申请号：US18559942

申请日：2022-04-28

Applicant: ASML NETHERLANDS B.V

Inventor： Derick Yun Chek CHONG ,  Pieter Cristiaan DE GROOT ,  Wouter Joep ENGELEN ,  Bogathi Vishnu, Vardhana REDDY

IPC: G02B5/18 ,  G02B27/00 ,  G03F7/00

Abstract: Diffraction gratings for a phase-stepping measurement system for determining an aberration map for a projection system are disclosed. The gratings are two-dimensional diffraction gratings for use as wafer level gratings in an EUV lithographic apparatus. In particular, the diffraction gratings include a substrate provided with a two-dimensional array of circular through-apertures and are self-supporting. In some embodiments, a ratio of the radius of the circular apertures to the distance between the centers of adjacent apertures may be selected to minimize the gain and cross-talk errors of a wavefront reconstruction algorithm. For example, the ratio may be between 0.34 and 0.38. In some embodiments, the circular apertures are distributed such that a distance between the centers of adjacent apertures is non-uniform and varies across the diffraction grating. For example, a local pitch of the grating may vary randomly across the diffraction grating.