Metrology of wavefront aberration of optics of EUV mask inspection systems

摘要

Disclosed is a test structure for measuring wavefront aberration of an extreme ultraviolet (EUV) inspection system. The test structure comprises a substrate of material having substantially no reflectivity for EUV light, and a portion of a multilayer stack formed as a pillar on the substrate. Likewise, a plurality of alternating pairs of layers having different refractive indices are provided to reflect the EUV light having a number equal to or less than 15 in pairs.