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 Si3N4 film. The fabrication process
starts with depositing Si3N4 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 Si3N4
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.
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