Platinum-based alloy absorber with improved etching properties for next-generation EUV mask

Abstract

Extreme ultraviolet (EUV) lithography is a critical technique for fabricating advanced semiconductor devices, and the development of a high numerical aperture (NA) system for future 3 nm nodes is currently in progress. The current Tabased EUV masks exhibit limited imaging performance attributed to mask 3D effects, thereby necessitating the development of alternative EUV masks. In this study, we propose platinum (Pt)-based alloys as the potential absorber materials that offer benefits in terms of both mask manufacturing and imaging performance. Despite the superior imaging performance of Pt due to its optical properties, its adoption as a mask absorber is difficult because of its low etchability. Therefore, tungsten (W) which has high reactivity with fluorine-based etch gas was introduced as an alloy material to lower intermolecular binding energy, and argon (Ar) ion implantation was employed to amorphize the thin film. We evaluated the etching properties of ion-implanted Pt-W alloy thin films using CF4/O2/Ar gas. As a result, we verified that the etch rate of the implanted alloy was about 1.86 times higher than that of Pt, resulting in a higher sidewall angle in patterns. Furthermore, based on PROLITH 2022a simulation tool, we confirmed that Pt-W alloys showed about 2.4 NILS at 34 nm thickness which is higher than the current Ta-based mask, and the best focus shift has been mitigated by 33 %. In conclusion, Pt-based materials have the potential to apply as the next-generation absorber for EUV masks that can achieve fine patterning and enhance imaging performance.