Coatings with barrier layers for extreme‐short wavelengths

Abstract

SummaryOver the last few decades, remarkable progress has been made in the field of multilayer coatings for the EUV spectral region, mainly due to the demands of EUV lithography for the semiconductor industry. The progress is associated with a deep understanding of the multilayer film growth, application of advanced smoothing technologies for multilayer interfaces, as well as the development of modern deposition and characterization techniques. The projection optics precisely coated by Mo/Si mirrors with 70 % reflectivity is the heart of the performance of industrial EUVL steppers recently developed by ASML for high‐volume chip production. While the EUVL at 13.5 nm has just launched into the market, the first high‐performance LaN/B multilayer mirrors with reflectivity up to 61 % were developed for the next emerging lithography generation with a reduced wavelength of 6.6 nm. Recent technological progress in EUVL optics and radiation sources triggered the development of compact microscopes in the water window spectral range (2.4 – 4.4 nm). The optimization of the multilayer design and deposition process of Cr/V, Cr/Sc and Cr/C mirrors resulted in reflectivity of 14.5% at 2.42 nm, 27.0 % at 3.16 nm, and 15,6% at a wavelength of 4.42 nm, respectively. These promising and still not limiting results indicate a large potential for future application of multilayer coated optics in various application fields such as microscopy in the water window, plasma diagnostics, spectroscopy, and astrophysics.

Three-dimensional coherent diffraction snapshot imaging using extreme ultraviolet radiation from a free electron laser

“…The 2D images obtained via the CDI reconstruction are [30,31]. Extension to higher photon energies, up to the water 214 window (300-500 eV) and beyond, towards the L-edges of 3d 215 transition metals (600-1000 eV), is technically possible by ex-216 ploiting state-of-the-art multilayer coatings [40]. Advances in 217 the fabrication of transmissive X-ray diffraction optics [41,42] 218 enable us to envision split-recombination systems based on such 219 optics, making this approach compatible even with hard X-rays.…”

A new framework for soft x-ray transient gratings

“…Such a crossing angle is likely feasible for soft x-ray reflective optics, since the transmission is above 10% (5%) up to E ph ≈ 800 eV (930 eV). The use of high reflecting multilayer coatings [16] can tangibly mitigate the reduction of TG visibility vs E ph , as well as the decrease in the transmission at large crossing angles and high photon energy, in particular in the relatively narrow spectral region for which the multilayer structure is optimized. Figure 3(b) indicates how the mirror-based approach imposes relevant challenges in reaching single digit nm values of L TG .…”

“…MLs working in such an angular range can nowadays be realized with, e.g. a peak reflectivity of 10% at E ph = 0.9 keV and a bandwidth of about 10 eV; in the future the performances of MLs could improve since the current trend of academic and industrial users of MLs is to go towards the soft x-ray range [16]. Note that the ∆t = 0 condition is possible when the distance B is sufficiently long and 2θ sufficiently large.…”