Fabrication of stair-case profiles with high aspect ratios for blazed diffractive optical elements

A novel method for the fabrication of four level structures using multiple electron beam exposures using very thin (50 80 nm) resist layers is presented. The patterns of the two exposure steps are stored in 20 nm thick metal layers by reactive ion etching (RIE) and lift-off. By stepwise etching into the underlying substrate, a stair-case profile can he obtained. The overlay of the lithography levels to an accuracy of some tens of nanometers is done using registration of alignment marks. The method has been successfully applied to the patterning of silicon which is suited for the manufacture of x-ray optical components, and of quartz which can be used for visible light DOEs.