Phosphorus-based compounds for EUV multilayer optics materials

Abstract

Abstract: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 range. References and links1. E. Spiller, Soft X-ray Optics (SPIE, Bellingham, 1994). 2. J. Larruquert, "Optical properties of thin film materials at short wavelengths," in Optical Thin Films and Coatings, A. Piegari, and F. Flory, eds. (Woodhead Publishing Limited, 2013). 415-417 (2013). 11. The direct application of the solid allotropes of sulphur (S) in multilayer structures is unlikely because of its high reactivity. For that reason instead of pure S some stable S-based compounds were considered for applications in multilayer structures. This is in spite of the fact that in this situation the increased chemical stability is achieved at the expense of the optical performance. Compounds of S with any material have higher absorbance for EUV radiation than that of pure S in the wavelength range where the application of S is favorable. Hence the elements to form compounds with S should be chosen using the two following criteria: 1) high chemical stability of the resulting compound; 2) optical constants of the resulting compound close to those of pure S. The analysis of the CXRO database of the optical constants indicates that the most promising candidates are boron (B), yttrium (Y), zirconium (Zr) and strontium (Sr). Obviously phosphorus-reach compounds are still the most attractive -these are B 2 S 3 , Y 2 S 3 , ZrS 2 and SrS. However B 2 S 3 , Y 2 S 3 and SrS are decomposed by water with the release of toxic H 2 S gas. Hence they do not meet the criterion of stability, and we focused on ZrS 2 . Our calculations for multilayers with ZrS 2 spacer indicate that ZrS 2 -based multilayer structures could only add to the B-based multilayer structures within a narrow 0.3 nm range above the L absorption edge of S.

Exploiting the P L_2,3 absorption edge for optics: spectroscopic and structural characterization of cubic boron phosphide thin films

“…6. The reduced transmission contrast indicates that the actual extinction coefficient of the grown c-BP is smaller than predicted by tabulated scatter factors, which would mean that the predicted reflectivity values of c-BP based multilayer mirrors by Medvedev et al [17], who employed the same approximated optical constants for their calculations, may be overestimated. Nevertheless, the demonstrated sharpness of the P L 2,3 -edge shows that it may still be exploited for the construction of a reflective multilayer mirror, provided that the c-BP thin films can be grown sufficiently thin and smooth.…”

“…Methods for fabricating optical elements that are operational around the Si L 2,3 and B K-edge are well established, however, many applications require optics that are highly transparent at energies within the bounds of this spectral range [6,[12][13][14][15]. Several studies have highlighted the M 4,5 and L 2,3 absorption edges of strontium (Sr) and phosphorus (P), respectively, as potential candidates for the construction of a transmission filter or reflective optic that would operate just below 130 eV [16,17]. The high reactivity of Sr renders this element effectively inapplicable, as any exposure to ambient conditions would result in a rapid deterioration of the optical element's quality [12,18].…”

Enhancement of soft X-ray reflectivity and interface stability in nitridated Pd/Y multilayer mirrors

“…Replacement of the B 4 C spacer with less absorbing B or Y gives an additional rise in the reflectivity of up to 65% for the Pd/Y multilayer at λ = 9.5 nm. The maximal possible reflectance is achieved for Pd/Sr or Pd/BP [12] multilayers (the last one is not shown in Fig. 1), exceeding 70%.…”

Determining crystal phase purity in c-BP through X-ray absorption spectroscopy

“…Its high thermal conductivity 1 , hardness, chemical stability, high neutron capture cross section [1][2][3] and electronic structure, make it a promising candidate for application in catalysis 4 , hightemperature electronic devices 5,6 , neutron detectors 7 and radiation protective coatings. Boron phosphide has also been suggested as a promising material for optical elements for extreme ultraviolet radiation, operating close to the L 2,3 absorption edge of the phosphorus 8,9 . Many studies have successfully grown this crystalline phase of boron phosphide; studies to further improve its structural quality are ongoing [1][2][3][10][11][12][13][14][15][16][17] .…”