Determination of the density of ultrathin films using X-ray standing waves

Determination of density of ultrathin films presents a basic challenge for the research of multilayer structures. The commonly used technique of grazing incidence X-ray reflectivity analysis does not provide unique solutions for the layers thinner than 10 nm. Solution to this problem was proposed and explored by measuring the fluorescence yield angular dependence from a thin marker layer, placed above the layer to be characterized. Using simultaneous analysis of grazing incidence X-ray reflectivity and angular dependent fluoresce yields from specially designed and fabricated structures, densities of thin La and LaN layers of 2-6 nm thicknesses have been obtained with approximately 5% precision

Nitrogen Passivation in La/B4C Layered Structures

In theory La/B4C multilayer mirrors are a most promising optical elements for the future generation of 6 nm photolithography tools. One of the most serious phenomena limiting the reflectivity of La/B4C mirrors is interface intermixing of La and B4C. Recent research on La/B4C multilayer mirrors with 3.4 nm bi-layer thickness has shown an intermixed interface layer with a thickness of more than 2 nm, i.e. more then half the multilayer period. Application of barriers that prevent intermixing for such a sort period multilayer will significantly reduce the optical contrast. One of the ways of suppressing interface intermixing is passivation of the La layer, for instance by nitridation. In this work we will present the results of X-ray photoelectron spectroscopy analysis of La nitride formation using N-ion and N2 treatment of the La layer. All samples have been deposited on super polished Si substrates and transferred from the deposition facility to the XPS spectrometer in vacuum to avoid contamination. N-ion post treatment produces two types of La nitride as can be deduced from the N1s spectrum (figure 1). The peak width of the lower binding energy (indicated as N-) represents a compound formed due to surface interaction of La with N2, the peak with higher binding energy represents a compound formed by interaction of La with N-ions. Tsarfati et al. [1] has connected the formation of two types of nitride with the formation of LaN inside the layer and La(N2) at the surface

Multilayers for the lithography generation beyond EUVL

A potential candidate for the new generation lithography beyond EUV is La/B4C multilayer optics for λ = 6.x nm. Achieving the highest possible reflectance at near normal (1.5°) incidence requires substantial practical improvement of the structural perfection of the multilayers. Pure La/B4C multilayers suffer from the formation of relatively thick interlayer at the interfaces. We have found that N-ion and N2 gas treatment of the multilayer interfaces strongly reduces interlayer formation and therefore enhances the multilayer optical contrast which leading to increase of the reflectivity at 6.x nm. The wavelength dependence of the La/B4C and LaN/B4C multilayer reflectivity has been studied in order to investigate the spectral properties of multilayers near B-absorption edge. Calculation of the maximal reflectance for La/B4C and LaN/B4C reflectivity for various wavelengths (figure 1) predicts significant gain in reflectance near the B absorption edge. We will present the influence of N-ions treatment on reflectivity properties of La/B4C multilayers near the B absorption edge and discuss the effect on throughput of an entire lithography system

Wavelength selection for multilayer coatings for the lithography generation beyond EUVL

Key in designing the next generation of EUVL optics, i.e. at the wavelength of 6.x nm, will be matching its optimum operational wavelength to that of the candidate light sources. Light sources might be based on Tb or Gd, and the published spectra of plasmas created from these materials show highest intensities at 6.5 and 6.8 nm respectively. The reflective properties of the La/B4C coating, one of the more promising multilayer compositions for 6.x nm, are mainly determined by the B optical constants, near its K absorption edge (6.6 nm). We have experimentally assessed the critical material properties required for making the choice on the next stage lithography wavelength. Calculations of the maximum reflectance for B-based multilayers show significant gain near the B absorption edge when fine tuned with experimentally obtained optical data from appropriate multilayer structures. Results notably differ from tabulated optical data. The wavelength dependency of B-based multilayer reflectivity has been experimentally studied for various La-, B-based multilayer structures, including La/B4C, LaN/B4C, La/B and LaN/B, together with predictions of their peak reflectance. These results are of direct relevance for the final wavelength choice and the evaluation of the beyond EUV perspective