Minimal zone plates for x-ray lithography

As feature widths in integrated circuits continue to decrease, patterning the smallest features has become more and more challenging. This is especially true for contact levels, where vias less than 50 nm diameter will be extremely difficult to print. However, since vias are typically well separated, they are readily patterned by using zone plates to focus x rays. Although zone plates have been used to focus x rays to small, spots for many years, it has generally been considered necessary to have more than about 10 zones to produce clean images, i.e., with minimal energy in the side lobes. However, we have found that zone plates useful for x-ray lithography may have small numerical apertures and as few as two zones, and still produce very small and clean images. (C) 2004 American Vacuum Society.