A major difference between EUV lithography and its conventional optical predecessors is the lack of a usable pellicle.
No material has been found that is both transmissive at the EUV lithography wavelength of 13.5nm and that has
sufficient structural integrity to serve as a pellicle. Therefore, during exposure to EUV light the mask is unprotected and accretes particles. This necessitates repeated cleanings of the mask, which raises concerns about changes in the mask induced by the cleaning process. It is only through metrology that these concerns can be addressed. This paper describes an optical characterization method to determine the effect of cleaning an EUV mask.
With pitches in the double-digit nanometer range and depths in the single-digit nanometer range, superior sensitivity is a
necessary metrology requirement for patterned media. Variations in depth, CD, and sidewall angle on the order of the
desired measurement precision will change the measured raw data by a miniscule amount, around one per cent or less.
It is shown that the required sensitivity can be achieved with polarized broad band reflectance and transmittance
incorporating optimized signal-to-noise and analysis based on Rigorous Coupled-Wave Analysis (RCWA) in
conjunction with the Forouhi-Bloomer dispersion equations for optical properties, n and k. The measurement capabilities
are demonstrated with simulations and examples of various DTR and BPM structures.
This study investigates a non-destructive optical metrology technique, that furnishes measurement solutions for hard
drive discrete track recording (DTR) and bit patterned media (BPM) templates and imprints. From the measurement and
analysis of polarized reflectance and transmittance, feature height and profile of DTR and BPM templates and imprints,
as well as residual layer thickness of imprints, are accurately determined, and uniformity maps of these parameters are
produced in a fraction of a minute. Simulations of theoretical polarized reflectance and transmittance, relating to next
generation structures, demonstrate that the optical metrology solution has capability for future products.