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Journal of Micro/Nanopatterning, Materials, and Metrology
VOL. 23 · NO. 4 | October 2024
ISSUES IN PROGRESS
IN PROGRESS
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Extreme ultraviolet (EUV) attenuated phase-shifting masks are complex structures with stringent requirements for manufacturing precision and materials properties, and they have been object of extensive research lately.
Aim
We aim to characterize the optical constants (n and k) and the thickness of the layers in the mask stack with a nondestructive method.
Approach
Using a spectral reflectometry approach with EUV and soft X-ray illumination at various incidence angles, different layer’s properties in a photomask blank can be selectively probed. The optical constants and the thicknesses of the layers can be obtained by fitting a suitable model to the experimental reflectance.
Results
The optical constants of the Pt-W alloy absorber and the thicknesses of the top three layers of the sample stack were accurately characterized.
Conclusions
Stacked layer’s properties can be selectively probed with the instrument (REGINE) we developed. The properties of the topmost layer can be characterized by assessing the probing depth, before investigating deeper layers with a suitable choice of illumination wavelength and angle of incidence.
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In extreme ultraviolet (EUV) photoresist exposure, the primary and secondary electrons drive chemistry rather than the EUV photons themselves. These electrons have a wide range of energies below approximately 80 eV, which are capable of complex network of reactions during exposure.
Aim
To better understand the ability of electrons of different energies within the EUV primary and secondary electron range, we want to characterize and compare the chemistry induced in pure polymer films by direct exposure to electrons.
Approach
Thin films of poly(tert-butyl methacrylate), poly(methyl methacrylate), and poly(4-hydroxystyrene) were exposed to a 20 to 80 eV electron beam. Outgassing during exposure was characterized in-situ using a quadrupole residual gas analyzer. The thickness changes were measured using ellipsometry and chemical bond structure data were collected using Fourier-transform infrared spectroscopy (FTIR) after exposure to compare different exposure conditions.
Results
Poly(4-hydroxystyrene) demonstrated stability during electron exposures. Exposures of the other two materials led to outgassing of protecting groups, the intensity of which decayed in time. Outgassing, FTIR, and thickness loss data exhibited approximately linear relationships to each other.
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