2.7 Nanolithography

The introduction of non-optical lithography has been announced several times during the last twenty years, but optical methods like projection lithography have always been extended beyond predicted limits. However, a further ``simple'' downscaling of the optical wavelength beyond 193 nm is not feasible because of the lack of refractive lenses and the problems involved in the fabrication of pure reflective systems with high enough numerical apertures. Hence, as already noted in the introduction, the need for new lithographic techniques is one of the big challenges for further progress in the semiconductor technology. At the moment, several approaches toward sub-100 nm lithography are under discussion.