Lithography based on the wavelength of 6.x nm is considered to be a potential extension of the current 13.5 nm EUV lithography. Light sources might be based on Tb or Gd. The published spectra of plasmas created from these materials show highest intensities at 6.5 and 6.8 nm respectively. Multilayer mirrors (MLMs) based on La and B show the highest optical contrast for the 6.6-7 nm wavelength range and a maximum reflectance at 6.64 nm, where the B absorption is minimal. It is not possible to design high reflective B-based mirrors for 6.5 nm because this would be below the B-K absorption edge. In theory the reflectivity of La/B MLMs at 6.8 nm is only a few percent lower than at the optimal wavelength of 6.64 nm, but measurements of real multilayer mirrors show a significantly larger reduction of reflectivity at 6.8 nm. The origin of this larger drop is the reduced optical contrast of the deposited La/B mirror with respect to theoretical case. In the presentation we will discuss how the multilayer structure influences its reflectivity profile and the ways to optimize La/B mirrors for 6.8 nm.
|Publication status||Published - 8 Oct 2012|
|Event||2012 International Workshop on EUV and Soft X-ray Sources - Dublin, Ireland|
Duration: 8 Oct 2012 → 11 Oct 2012
|Conference||2012 International Workshop on EUV and Soft X-ray Sources|
|Period||8/10/12 → 11/10/12|