The influence of line edge roughness and CD uniformity on EUV scatterometry for CD characterization of EUV masks
Cell Transformation, Viral
Receptors, Cell Surface
Scatterometry, the analysis of light diffracted from a periodic structure, is a versatile metrology for characterizing periodic structures, regarding critical dimension (CD) and other profile properties. For extreme ultraviolet (EUV) masks, only EUV radiation provides direct information on the mask performance comparable to the operating regime in an EUV lithography tool. With respect to the small feature dimensions on EUV masks, the short wavelength of EUV is also advantageous since it provides more diffraction orders as compared to UV. First measurements using PTB's EUV reflectometer at the storage ring BESSY II showed that it is feasible to derive information on the line profile in periodic areas of lines and spaces by means of rigorous numerical modeling. A prototype EUV mask with a matrix of test fields each divided into subfields containing among others test fields with lines&spaces was used for the measurements. In this contribution we summarize our present results in determining line profile parameters using scatterometry and reflectometry to provide the input data for the determination of CD and side-wall geometry using rigorous calculations of EUV diffraction. Particularly, we present a first investigation on the influence of line edge roughness and CD uniformity by correlating in-plane scatterometry data for the discrete diffraction orders corresponding to the pitch of the structure to out-of-plane measurements of diffusely scattered light induced by line edge roughness and CD uniformity. We demonstrate the influence of diffuse scattering on the determination of CD and side-wall geometry using only the discrete in-plane diffraction orders. To this aim we perform finite element (FEM) simulations on 2D computational domains.