Imaging of EUV Lithographic Masks with Programmed Substrate Defects

Abstract

Extreme ultraviolet lithographic masks with programmed defects on the mask substrates have been imaged to study substrate defects printability. Imaging was performed with a 2-aspherical-mirror system operating at 14 nm wavelength. Results showed that 25 nm thick substrate defects caused observable distortions of resist patterns. Defects of sizes approximately half the minimum resolvable features resulted in 15%-20% variations in resist linewidths. However, since the imaging system was operating at a reduced resolution due to misalignments of the optics, the effect of the defects may have been partially concealed by the phase front distortions caused by mirror misalignments.