XUV spectra of 2nd transition row elements: identification of 3d–4p and 3d–4f transition arrays

The use of laser produced plasmas (LPPs) in extreme ultraviolet/soft x-ray lithography and metrology at 13.5 nm has been widely reported and recent research efforts have focused on developing next generation sources for lithography, surface morphology, patterning and microscopy at shorter wavelengths. In this paper, the spectra emitted from LPPs of the 2nd transition row elements from yttrium (Z = 39) to palladium (Z = 46), with the exception of zirconium (Z = 40) and technetium (Z = 43), produced by two Nd:YAG lasers which delivered up to 600 mJ in 7 ns and 230 mJ in 170 ps, respectively, are reported. Intense emission was observed in the 2–8 nm spectral region resulting from unresolved transition arrays (UTAs) due to 3d–4p, 3d–4f and 3p–3d transitions. These transitions in a number of ion stages of yttrium, niobium, ruthenium and rhodium were identified by comparison with results from Cowan code calculations and previous studies. The theoretical data were parameterized using the UTA formalism and the mean wavelength and widths were calculated and compared with experimental results.

[1]  Hans M. Hertz,et al.  Liquid-nitrogen-jet laser-plasma source for compact soft x-ray microscopy , 2005 .

[2]  S. Goldsmith,et al.  Classification of Transitions in the euv Spectra of Y ix–xiii, Zr x–xiv, Nb xi–xv, and Mo xii–xvi* , 1971 .

[3]  J. Reader,et al.  3p 6 3d 8 –3p 5 3d 9 transitions in ironlike ions from Ru 18+ to Gd 38+ , 1988 .

[4]  M. Finkenthal,et al.  Identification of Mo XV to Mo XXXIII in the soft X-ray spectrum of the TFR Tokamak , 1977 .

[5]  V. Kaufman,et al.  Wavelengths and energy levels of the K i isoelectronic sequence from copper to molybdenum , 1989 .

[6]  Toyohiko Yatagai,et al.  Rare-earth plasma extreme ultraviolet sources at 6.5―6.7 nm , 2010 .

[7]  J. Reader,et al.  3p 6 3d 8 –3p 5 3d 9 transitions in Sr xiii, Y xiv, Zr xv, Nb xvi, and Mo xvii , 1981 .

[8]  Tsuyoshi Yamada,et al.  LPP-EUV light source development for high volume manufacturing lithography , 2013, Advanced Lithography.

[9]  J. Wyart,et al.  Spectra of the Manganese-Like Ions from Y XV to Ag XXIII , 1983 .

[10]  Y. Chushkin,et al.  Nanometer-scale period Sc/Cr multilayer mirrors and their thermal stability , 2006 .

[11]  M. Klapisch,et al.  Interpretation of unresolved transition arrays in the soft-x-ray spectra of highly ionized molybdenum and palladium , 1982 .

[12]  Hiroyuki Furukawa,et al.  Plasma physics and radiation hydrodynamics in developing an extreme ultraviolet light source for lithographya) , 2008 .

[13]  M. Klapisch,et al.  3d-4p transitions in the soft X-ray spectra of Mo XIV and of isoelectric Y to Ag ions, from a low-inductance vacuum spark , 1981 .

[14]  K. Koshelev,et al.  Physical processes in EUV sources for microlithography , 2011 .

[15]  H. Hertz,et al.  High‐resolution compact X‐ray microscopy , 2007, Journal of microscopy.

[16]  Klapisch,et al.  Variance of the distributions of energy levels and of the transition arrays in atomic spectra. III. Case of spin-orbit-split arrays. , 1985, Physical review. A, General physics.

[17]  Bowen Li,et al.  Feasibility study of broadband efficient ''water window'' source , 2012 .

[18]  Akira Endo,et al.  Spectra of plasmas of Ru, Rh, Pd and Mo produced with nanosecond and picosecond laser pulses , 2015, Europe Optics + Optoelectronics.

[19]  J. Reader,et al.  3p 6 3d 9 –3p 5 3d 10 transitions of cobaltlike ions from Sr 11+ to U 65+ , 1987 .

[20]  Chihiro Suzuki,et al.  Sources for beyond extreme ultraviolet lithography and water window imaging , 2015 .

[21]  J. Wyart,et al.  The 3d9-3d84p Transitions in the Spectra of Highly-Ionized Elements Yttrium to Silver (Y XIII-Ag XXI) , 1982 .

[22]  J. Reader,et al.  3d–4p Transitions in the zinclike and copperlike ions Y x, xi; Zr xi, xii; Nb xii, xiii; and Mo xiii, xiv , 1981 .

[23]  C. Suzuki,et al.  Spectroscopy of highly charged ions and its relevance to EUV and soft x-ray source development , 2015 .

[24]  J. Wyart,et al.  Extended analysis of 3d-4p transitions in copper like ions of the sequence Ge3+-Mo13+ , 1984 .

[25]  J. Reader,et al.  Spectra of the cobaltlike ions Sr xii, Y xiii, Zr xiv, Nb xv, and Mo xvi , 1982 .

[26]  P. Burkhalter,et al.  Spectra of Nb XII-XVII from a low-inductance vacuum spark , 1982 .

[27]  G. Tonon,et al.  X‐ray emission in laser‐produced plasmas , 1973 .

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

[29]  J. Wyart,et al.  Spectra of the Ironlike Ions from Y XIV to Ag XXII , 1983 .

[30]  G. McDermott,et al.  Visualizing cell architecture and molecular location using soft x-ray tomography and correlated cryo-light microscopy. , 2012, Annual review of physical chemistry.

[31]  M. Finkenthal,et al.  Nickel-like spectra of elements Y xii to Ag xx from a vacuum spark , 1981 .

[32]  Bowen Li,et al.  “Water window” sources: Selection based on the interplay of spectral properties and multilayer reflection bandwidth , 2013 .

[33]  J. Sugar,et al.  Energy Levels of Molybdenum, Mo I through Mo XLII , 1988 .

[34]  E. Gullikson,et al.  Atomic scale interface engineering by modulated ion-assisted deposition applied to soft x-ray multilayer optics. , 2008, Applied optics.