Wideband multilayer mirrors with minimal layer thicknesses variation

Wideband multilayers designed for various applications in hard X-ray to Extreme UV spectral regions are based on a layered system with layer thicknesses varying largely in depth. However, because the internal structure of a thin film depends on its thickness, this will result in multilayers in which material properties such as density, crystallinity, dielectric constant and effective thickness vary from layer to layer. This variation causes the fabricated multilayers to deviate from the model and negatively influences the reflectivity of the multilayers. In this work we solve this problem by developing designs of wideband multilayers with strongly reduced layer thickness variations in depth, without essential degradation of their optical characteristics

Resolving buried interfaces with Low Energy Ion Scattering

We investigate the use of Low Energy Ion Scattering (LEIS) to characterize buried interfaces of ultra-thin films. LEIS spectra contain depth-resolved information in the so-called sub-surface signal. However, the exact correlation between the sub-surface signal and the depth composition is still unknown. For this reason, LEIS spectra so far only provided qualitative information about buried interfaces. In this study, we investigate nm-thin films of Si-on-W and Si-on-Mo, where we compare simulated data to LEIS spectra. We present a method to extract depth-sensitive compositional changes -- resolving buried interfaces -- from LEIS spectra for the first few nanometers of a thin film sample. In the case of Si-on-Mo, the simulation of the LEIS sub-surface signal allows obtaining a quantitative measurement of the interface profile that matches the value determined using the LEIS layer growth profile method with an accuracy of 0.1 nm. These results pave the way to further extend the use of LEIS for the characterization of features buried inside the first few nanometers of a sample.Comment: 25 pages, 11 figure

Phosphorus-based compounds for EUV multilayer optics materials

We have evaluated the prospects of phosphorus-based compounds in extreme ultraviolet multilayer optics. Boron phosphide (BP) is suggested to be used as a spacer material in reflective multilayer optics operating just above the L-photoabsorption edge of P (λ ≈9.2 nm). Mo, Ag, Ru, Rh, and Pd were considered for applications as reflector materials. Our calculations for multilayer structures with perfect interfaces show that the Pd/BP material combination suggests the highest reflectivity values, exceeding 70% within the 9.2 – 10.0 nm spectral range. We also discuss the potential of fabrication of BP-based multilayer structures for optical applications in the extreme ultraviolet rang

Surface and sub-surface oxidation of thin films using Low Energy Ion Scattering

Ru and ZrN are candidate capping layers for applications such as catalysis, electronics and optical coatings: Ru exhibits a low resistivity, high thermal stability, excellent oxidation resistance and good diffusion capabilities. ZrN is thermally stable, and is known for its good mechanical properties. Although the oxidation process has been studied for both materials, the surface and especially the sub-surface oxidation is not properly understood and well addressed. We use the sub-monolayer surface sensitivity of the low energy ion scattering (LEIS) technique for in-situ monitoring of surface oxidation and determination of the oxygen sticking probabilities. From the LEIS in-depth signal, sub-nanometer sub-surface oxidation can be determined as a function of time and from these data oxygen diffusion constants can be extracted. These data support the applications for which adequate protecting surface films are required. i) Author to whom correspondence should be addressed. Electronic mail: [email protected]

High reflectance La/B based multilayer mirrors for 6.x nm wavelength

For future photolithography processes, the wavelength of 6 nm may offer improved imaging specs. The perspective of this technology however, will depend critically on the performance of multilayer reflective mirrors, which are likely to be based on La/B. One of the issues is formation of LaxBy compounds at the interfaces, which decreases the optical contrast and reduce the reflectivity. To prevent such chemical interaction, passivation of La by nitrogen has been investigated. We successfully synthesized LaN layers that resulted in a new world record reflectivity of 64% at 6.6 nm at near normal incidence. This reduces the gap to the target of 70%, desired for a next generation lithography.</p

Surface and sub-surface thermal oxidation of thin ruthenium films

A mixed 2D (film) and 3D (nano-column) growth of ruthenium oxide has been experimentally observed for thermally oxidized polycrystalline ruthenium thin films. Furthermore, in situ x-ray reflectivity upon annealing allowed the detection of 2D film growth as two separate layers consisting of low density and high density oxides. Nano-columns grow at the surface of the low density oxide layer, with the growth rate being limited by diffusion of ruthenium through the formed oxide film. Simultaneously, with the growth of the columns, sub-surface high density oxide continues to grow limited by diffusion of oxygen or ruthenium through the oxide fil