Spectral properties of La/B--based multilayer mirrors near the boron K absorption edge.

The spectral properties of La/B, La/B(4)C, and LaN/B, LaN/B(4)C multilayer mirrors have been investigated in the 6.5-6.9 nm wavelength range based on measured B and B(4)C optical constants. Experimentally it is verified to what extent measured and tabulated optical constants are applicable for simulations of the reflectivity of these short period multilayer mirrors. The measured maximum reflectance at various wavelength values around the boron-K absorption edge is compared to calculated values from model systems. The measured reflectance profiles of La/B and La/B(4)C show a maximum at a slightly larger wavelength than calculations would predict based on the measured B and B(4)C optical constants. This is explained by the influence of a formed boron-lanthanum compound on the wavelength where the multilayer shows maximum reflectance. The maximum reflectance profiles of LaN/B and LaN/B(4)C multilayers can be described accurately by using the same boron atomic scattering factors, indicating boron in the LaN/B(4)C multilayer to be in a similar chemical state as boron in the LaN/B multilayer. It also indicates that nitridation of the La layer in the multilayer prevents the formation of La-B compounds. We show that the optimal wavelength for boron based optics is about 6.65 nm and depends on the B chemical state. Finally, using the measured B optical constants we are able to calculate the spectral response of the multilayers, enabling the prediction of the optimal parameters for the above mentioned multilayers.

[1]  L. G. Parratt.  Surface Studies of Solids by Total Reflection of X-Rays , 1954 .

[2]  Charles M. Falco,et al.  Survey of Ti-, B-, and Y-based soft x-ray-extreme ultraviolet multilayer mirrors for the 2- to 12-nm wavelength region. , 1996, Applied optics.

[3]  Eric Louis,et al.  Nanometer interface and materials control for multilayer EUV-optical applications , 2011 .

[4]  Andreas Fischer,et al.  Status of EUV reflectometry at PTB , 2013, Advanced Lithography.

[5]  D. Ksenzov.  Interaction of femtosecond X-ray pulses with periodical multilayer structures , 2010 .

[7]  F. Bridou,et al.  La/B4C small period multilayer interferential mirror for the analysis of boron , 2005 .

[8]  David L. Windt,et al.  IMD—software for modeling the optical properties of multilayer films , 1998 .

[9]  Eric Louis,et al.  Nitridation and contrast of B4C/La interfaces and X-ray multilayer optics , 2010 .

[10]  B. Morosin,et al.  Structures of the Boron-Rich Boron Carbides from Neutron Powder Diffraction: Implications for the Nature of the Inter-Icosahedral Chains , 1996 .

[11]  U. Pietsch,et al.  Optical properties of boron carbide near the boron K edge evaluated by soft-x-ray reflectometry from a Ru/B(4)C multilayer. , 2009, Applied optics.

[12]  B. L. Henke,et al.  X-Ray Interactions: Photoabsorption, Scattering, Transmission, and Reflection at E = 50-30,000 eV, Z = 1-92 , 1993 .

[13]  N. I. Chkhalo,et al.  Multilayer X-ray mirrors based on La/B4C and La/B9C , 2010 .

[14]  E. Spiller.  Refractive index of amorphous carbon near its K-edge. , 1990, Applied optics.

[15]  Regina Soufli,et al.  Optical constants of electron-beam evaporated boron films in the 6.8-900 eV photon energy range. , 2007, Journal of the Optical Society of America. A, Optics, image science, and vision.

[16]  B. Zeldovich,et al.  X-ray and far uv multilayer mirrors: principles and possibilities. , 1977, Applied optics.

[17]  S S Churilov,et al.  EUV spectra of Gd and Tb ions excited in laser-produced and vacuum spark plasmas , 2009 .

[18]  N. Ceglio,et al.  Wavelength considerations in soft-x-ray projection lithography. , 1993, Applied optics.

[19]  S. A. Gusev,et al.  Multilayered mirrors based on La/B4C(B9C) for X-ray range near anomalous dispersion of boron (λ≈6.7 nm) , 2009 .

[20]  F. Salmassi,et al.  Optical constants of magnetron-sputtered boron carbide thin films from photoabsorption data in the range 30 to 770 eV. , 2008, Applied optics.

[21]  Eric Louis,et al.  Reflective multilayer optics for 6.7 nm wavelength radiation sources and next generation lithography , 2009 .