Investigating printability of native defects on EUV mask blanks through simulations and experiments
2014
Availability of defect-free masks is considered to be a critical issue for enabling extreme
ultraviolet lithography (EUVL) as the next generation technology. Since completely defect-free
masks will be hard to achieve, it is essential to have a good understanding of the defect
printability as well as the fundamental aspects of a defect that result in the defects being printed.
In this work, the native mask blank defects were characterized using atomic force microscopy
(AFM) and cross-section transmission electron microscopy (TEM), and the defect printability of
the characterized native mask defects was evaluated using finite-difference time-domain (FDTD)
simulations. The simulation results were compared with the through-focus aerial images obtained
at the SEMATECH Actinic Inspection Tool (AIT) at Lawrence Berkeley National Lab (LBNL)
for the characterized defects. There was a reasonable agreement between the through-focus
FDTD simulation results and the AIT results. To model the Mo/Si multilayer growth over the
native defects, which served as the input for the FDTD simulations, a level-set technique was
used to predict the evolution of the multilayer disruption over the defect. Unlike other models
that assume a constant flux of atoms (of materials to be deposited) coming from a single
direction, this model took into account the direction and incident fluxes of the materials to be
deposited, as well as the rotation of the mask substrate, to accurately simulate the actual
deposition conditions. The modeled multilayer growth was compared with the cross-section
TEM images, and a good agreement was observed between them.
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