Demagnification in proximity x-ray lithography and extensibility to 25 nm by optimizing Fresnel diffraction

This new understanding and demonstration of features printed by proximity x -ray lithography allows a revolutionary extension and simplification of oth erwise established processes for microfabrication. The ability to produce f ine features is controlled predominantly by diffraction and photoelectron b lur. The diffraction manifests itself as feature 'bias'. In the classical a pproach the bias is minimized. Bias optimization in terms of mask/wafer gap and resist processing allows the formation, on a wafer, of features smalle r than those on the mask: thus producing local 'demagnification'. This dema gnification (x3 - x6) is achieved without lenses or mirrors, but it offers the same advantages as projection optical lithography in terms of critical dimension control. The photoelectron blur is more or less pronounced depend ing on exposure dose and development conditions. Resist exposure and proces s can be optimized to utilize a similar to 50% photoelectron energy loss ra nge. In consequence proximity x-ray lithography is extensible to feature si zes below 25 nm, taking advantage of comparatively large mask features (>10 0 nm) and large gaps (30-15 mu m). The method is demonstrated for demagnifi cation values down to x3.5. To produce DRAM half-pitch fine features, techn iques such as multiple exposures with a single development step are propose d.