Pt-W alloy absorbers for high-NA EUV lithography: tunable optical and etching performance

Abstract

Extreme ultraviolet lithography is used to mass-produce nanoscale integrated circuits, and high-numerical-aperture systems for 3 nm technology nodes are currently being developed. However, conventional tantalum-based EUV masks face limitations in terms of resolving fine patterns. This study introduces platinum-tungsten alloys as alternative absorber materials that are advantageous from both imaging performance and manufacturability perspectives. Although Pt offers excellent optical properties, including high EUV absorption and phase-shifting capabilities owing to its high extinction coefficient and low refractive index, its poor etchability limits its direct applicability. To overcome this limitation, we alloyed platinum with tungsten, which readily forms highly volatile reaction products with fluorine-based etching gases. The inclusion of W enhanced the etchability of Pt without degrading its optical benefits. Simulations revealed that Pt-W alloys not only improve imaging performance and mitigate mask 3D effects compared to conventional absorbers but also require lower exposure doses than pure Pt. Furthermore, we showed that increasing the W content enhances the etching rate and results in more-vertical sidewall profiles devoid of etch residue. These results demonstrate that Pt-W alloys are promising candidates for next-generation EUV mask absorbers.