Moving towards significantly smaller nanostructures, direct structuring techniques such as electron beam lithography approach fundamental limitations in feature size and aspect ratios. Application of nanostructures like diffractive X-ray lenses require feature sizes of below 10 nm to enter a new regime in high resolution X-ray microscopy. As such dimensions are difficult to obtain using conventional electron beam lithography, we pursue a line-doubling approach. We demonstrate that this method yields structure sizes as small as 6.4 nm. X-ray lenses fabricated in this way are tested for their efficiency and microscopic resolution. In addition, the line-doubling technique is successfully extended to a six-fold scheme, where each line in a template structure written by electron beam lithography evolves into six metal lines.
Both multilayer period thickness expansion and compaction were observed in Mo/B4C multilayers upon annealing, and the physical causes for this were explored in detail. Using in situ time-dependent grazing incidence X-ray reflectometry, period changes down to picometer-scale were resolved. It was shown that the changes depend on the thickness of the B4C layers, annealing temperature, and annealing time. Although strong stress relaxation during annealing was observed, it was excluded as a cause for period expansion. Auger electron spectroscopy and wide angle X-ray diffraction measurements revealed the growth of interlayers, with associated period changes influenced by the supply of B and C atoms to the growing compound interlayers. For multilayers with a Mo thickness of 3 nm, two regimes were recognized, depending on the deposited B4C thickness: in multilayers with B4C ≤ 1.5 nm, the supply of additional Mo into the already formed MoBxCy interlayer was dominant and led to densification, resulting in period compaction. For multilayers with B4C ≥ 2 nm, the B and C enrichment of interlayers formed low density compounds and yielded period expansion.
The thermal stability of La/B and LaN/B multilayers was investigated. The two multilayer systems were found to have comparable subångström period expansion upon annealing in the temperature range of 250°C to 400°C. For La/B multilayers, wide angle x-ray diffraction analysis revealed that the size of LaB 6 crystallites present did not change significantly upon thermal treatment. Using grazing incidence x-ray reflectometry, strong change in the internal structure due to interdiffusion at the interfaces of La/B multilayers was observed after annealing. This, coupled to the unchanged crystallinity, suggested the growth of amorphous lanthanum boride interlayers. At wavelength reflectance, measurements showed that as-deposited LaN/B multilayers had an enhanced optical contrast compared with La/B. During thermal loading, the rate of diffusion-induced reflectance decrease in LaN/B multilayers was slower than in La/B. The enhanced thermal stability of LaN/B was attributed to the slower growth of LaN-B interfaces compared with La-B.
A surface structured extreme ultraviolet multilayer mirror was developed showing full band suppression of UV (λ=100-400 nm) and simultaneously a high reflectance of EUV light (λ=13.5 nm). The surface structure consists of Si pyramids, which are substantially transparent for EUV but reflective for UV light. The reflected UV is filtered out by blazed diffraction, interference, and absorption. A first demonstration pyramid structure was fabricated on a multilayer by using a straightforward deposition technique. It shows an average suppression of 14 times over the whole UV range and an EUV reflectance of 56.2% at 13.5 nm. This robust scheme can be used as a spectral purity solution for all XUV sources that emit longer wavelength radiation as well.
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