Large area interference lithography using a table-top extreme ultraviolet laser: a systematic study of the degree of mutual coherence

A prototype low cost table-top Ar capillary discharge laser source (1.5?ns pulse duration, ? = 46.9?nm) was successfully used to produce, by means of interference lithography (with a simple Lloyd mirror setup), large area (0.1?mm2) regular patterns from 400?nm down to 22.5?nm (half-pitch) on PMMA/Si (PMMA: polymethylmethacrylate) substrates. The experiments allowed a systematical investigation of the degree of mutual coherence of the source, giving a clear indication that the interference lithography can be pushed down to the ultimate resolution limit of ?/4.