Surface relief structures with linewidths below 2000 Å

We describe techniques for producing high-aspect-ratio vertical-walled relief gratings of 1600 Å linewidth with smooth line edges in SiO2 and Si substrates. Soft x-ray lithography (13.3–44.7 Å) is first used to expose such structures in PMMA. Liftoff of chromium and reactive sputter etching in CHF3 gas are then used to transfer the structure into the SiO2.