My proposal EUVPLASMA addressed the “EUV source challenge” (EUV stands for extreme ultraviolet light as used in state-of-the-art lithography) through four Objectives: (1) create insight into tin-droplet deformation and fragmentation for optimal target preparation through laser-pulse impact, the first step of the two-step sequence used to produce EUV light; (2) provide understanding of the myriad of atomic plasma processes responsible for the emission of EUV light in the second step of the process; (3) understand and push the fundamental limit of this plasma-conversion of laser light into EUV light; and (4) explain and control how the laser-produced plasma expands.
Rapidly since the start of the implementation of the action significant advances have been made towards reaching all four objectives.
The project quickly moved from a development phase towards a stage where first results could be produced. Rapid progress towards meeting Objective 1 was achieved already in the first reporting period with a first paper in a crucial step towards a full understanding explosive tin-droplet deformation and fragmentation for optimal droplet-target preparation. Further high-quality papers have been published over the course of the action on the topic of laser-induced deformation and vaporization of a stretching sheet of liquid tin, a crucial step towards a full understanding explosive tin-droplet deformation and fragmentation for optimal droplet-target preparation. A major discovery was made early on by the PI in a larger collaborative effort, related to the true atomic origins of extreme ultraviolet light in laser-produced tin plasma, and was published in a high impact journal (titled “Prominent contribution…”, Nature Commun. 11, 1-8 (2020)). This finding enabled meeting Objective 2 by identifying and obtaining key data of the relevant atomic plasma processes. This breakthrough enabled further work to focus on radiation-hydrodynamics modeling and with it to progress beyond the defined work packages to understand the full energy balance in laser-driven plasma, including in particular towards meeting Objective 4 – enabling to control how the laser-produced plasma expands, and also towards meeting Objective 1 (see above). Several high-quality publications (including an Editor’s pick) appeared on the topic of Objective 4, which over the course of the action has drawn significant attention and its importance to the overall action increased, leading to a particular focus on obtaining experimental data towards meeting Objective 4. Several experimental papers on (i) methods on usage of ion detectors [an electrostatic analyzer (ESA) and retarding-grid analyzer Faraday cups (RFAs)], as envisaged in the DoA and on (ii) the physics of plasma expansion, teaming up with the modeling efforts elegantly combining theory and experiments in key publications. Later in the action, the modeling efforts also strongly contributed to Objective 3 with a focus publication on a study of the dependence of key plasma properties on `drive’ laser wavelength dependence.
Experimental work towards meeting Objective 3 started in line with the DoA planning, using a pre-developed mid-infrared laser system to laser-produce plasma and reached record-high conversion efficiencies of converting drive laser light into useful EUV photons using 2-micrometer wavelength laser – this is a key breakthrough enabled by the action. Several publications on the topic meanwhile appeared in the public literature. Record-high conversion efficiencies of converting mid-infrared drive laser light into useful EUV photons using tin plasma were achieved as published in a special issue of Applied Physics Letters, dedicated to (and titled) “Plasma Sources for Advanced Semiconductor Applications” that was initiated and co-edited by the PI. We note that the impact of this action on science and society continues to be strengthened by the continuous and frequent exchange of ideas and data with semiconductor equipment manufacturer ASML enabling translating results achieved in the laboratory to a relevant industrial setting thus providing part of the basis for building tomorrow’ bright and stable plasma sources for EUVL, while significantly progressing the related fields of physics.
