Method Development: EUV interference lithography

The research is focused on the investigation of resolution limits of interference and proximity lithography with EUV radiation. Various types of laboratory EUV sources were examined with regard to yielding the highest pattern density and quality. In particular, these are Xenon gas-discharge plasma source (broadband radiation near 11 nm wavelength), Ne-like Ar-plasma-based EUV laser (coherent narrow-band radiation at 46.9 nm), and high-harmonic generation (HHG) source (at 29 nm). Also different interference lithography approaches are implemented and investigated experimentally. These included reflective interference lithography with Lloyd’s mirror, proximity lithography, and different types of Talbot lithography (see Fig. 5) [1-4]. This is complemented by numerical simulations of optical wave propagation of EUV radiation to predict limits of the resolution and contrast for these approaches. General research objectives are analysis of optical characteristics of particular EUV sources with respect to the patterning capabilities, optimization of the optical design of interference lithography system for the use of EUV radiation, and understanding of limits of different methods.
Large-area arrays of complex nano-antennes using laboratory-based EUV proximity lithography were fabricated in cooperation with RWTH-TOS and RWTH-Infrared- Nano-Optics institutes. Precise control over the mask-wafer distance and the exposure dose increases the flexibility of the diffraction-assisted EUV lithography and allows for generation of a variety of different nanostructures using one and the same mask [2].
For the non-paraxial case we theoretically investigated the scalability of Talbot EUV lithography. The FDTD simulation has shown that achromatic and fractional Talbot lithography with amplitude transmission masks can be used effectively for nanostructuring and pitch demagnification [1,4]. The practical resolution limit in the achromatic Talbot regime is 7.5 nm half-pitch using TE polarized light.