A new absorbing stack for EUV masks

Extreme Ultraviolet (EUV) masks are composed of EUV-reflective regions (multilayer) and of EUV-absorbing regions (patterned areas). The choice of materials for the absorbing stack (i.e. the buffer layer and the absorber layer) is crucial for providing good optical performances. This choice has to take into account three major issues: optical aspects (EUV and DUV performances, aerial image); repair feasibility and technological feasibility (deposition, etching, stripping...); ageing and utilization aspects: stability of the stack, cleaning capability. In this paper, a new absorbing stack A/B is proposed: this stack completely fulfils optical specifications and its total thickness is much lower than those found in the literature, with absorbing materials like TiN, Cr or TaN for instance. This thin thickness enables to reduce shadowing effects, which is particularly interesting for very advanced nodes. Experimental studies were then carried out on this new stack. We focused on two major topics: low temperature deposition and wet etching feasibility of B-material.