Application of ≊100 Å linewidth structures fabricated by shadowing techniques

A variety of shadowing techniques have been developed for fabricating simple structures with lines and spaces in the 100 Å linewidth regime. In the basic technique, a smooth vertical step with precisely determined depth is produced in a substrate by reactive ion etching. This step is shadowed at a shallow angle by evaporation in order to deposit material on the vertical wall. The substrate is then etched at normal incidence with an ion beam to remove the thin layer of material outside the step. This leaves a thin rectangular line of material at the step. By alternately evaporating different materials and by adding lithography and etching steps, more complex structures can be made. Applications of these structures in wire grating optical polarizers and the use of long thin wires for studying electron localization are described. Optical polarizers with extinction ratios of nearly 200 to 1 have been made. This demonstrates some of the unique capabilities of the shadowing technique since high quality polarizers require large areas of high aspect ratio ≊100 Å linewidth metal lines.