Fabrication of transmission gratings for extreme ultraviolet interference lithography

摘要

Transmission gratings with a period of 100 nm for extreme ultraviolet interference lithography are fabricated with 2 groups of 50 nm thick Cr bars on a 100 nm thick Si_3N_4 film. The fabrication process starts with depositing Si_3N_4 on both sides of (100) Si wafers by LPCVD, followed by electron beam lithography of ZEP520A resist, evaporation of Cr and resist lift-off. A 120 nm thick stop layer of Au is then evaporated onto the surrounding area to eliminate unwanted transmission. Finally, a pair of Si_3N_4 windows are opened on the back side by dry etching, and the Si under the grating pattern is removed by KOH anisotropic wet etching. Diffraction measurement shows an acceptable first order efficiency of the gratings at the wavelength of 13.4 nm. Using the fabricated gratings at the interference lithography beam line of Shanghai Synchrotron Radiation Facility, economic and efficient fabrication of gratings with a doubled pitch, namely 50 nm period gratings, can be expected.