Alternative EUV absorptive materials and novel architectures for EUV reticle in nm node technology scanner

The 3D effects of typical EUVL masks worsen at higher numerical aperture of the imaging optics
employed in EUVL scanners. Therefore, the height of the EUV absorber layer of the reticle for
7nm node technology scanners necessarily should be reduced to the order of 30nm, as compared
to current Ta-based absorber heights which are around 50nm. Such a reduction of the absorber
height requires higher absorption per unit height or, more specifically, a higher absorption
coefficient. In this regard, the implementation of high EUV absorptive materials such as nickel
and silver were suggested. Nickel and silver grow polycrystalline which can be disadvantageous
in terms of the etching process used. Moreover, silver grows on ruthenium such that the surface
roughness is significantly unacceptable in terms of the surface roughness requirement for the
absorber layer of the reticle. As a result of these practical restrictions, two different designs were
suggested to overcome the practical issues; doping a nickel thin film with boron to suppress the
crystallization and a silver-germanium multilayer to suppress the crystallization and reduce the
surface roughness of the silver. The validations represented in section 7 showed both designs
successfully overcame the corresponding practical issues. Next, according to suggested designs,
full-size reticles must be fabricated to undergo further analyses by other stakeholders, such as
imaging tests, patterning, cleaning, and repair in order to provide further input to optimize and
validate final EUV absorber layers for 7nm node technology reticles.