Evaluation of EUV scatterometry for CD characterization of EUVmasks using rigorous FEM-Simulation

摘要

Scatterometry, the analysis of light diffracted from a periodic structure, is a versatile metrology for characterizingperiodic 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 EUVlithography tool. With respect to the small feature dimensions on EUV masks, the short wavelength of EUV is alsoadvantageous since it increases the sensitivity for small structural details. Measurements using PTB's EUV reflectometerat the storage ring BESSY II showed that it is feasible to derive information on the absorber line profile in periodic areasof lines and spaces by means of rigorous numerical modeling with the finite element method (FEM). A prototype EUVmask with fields of nominally identical lines was used for the measurements. In this contribution we correlate thescatterometry data to CD-SEM and surface nano probe measurements of the line profiles as provided by the masksupplier. We discuss status of the determination of CD and side-wall geometry by scatterometry using rigorous FEMcalculations of EUV diffraction and directions for further investigations.