Improved cost-of-ownership for a droplet-based LPP light source for HVM EUV mask and blank inspection (Conference Presentation)

Key components for the EUV mask infrastructure include actinic AIMS and pattern inspection, which are crucial for the introduction of EUV lithography into HVM. The usage of pellicles further substantiates the need for actinic light sources. EUV light sources with a high availability and brightness are required to increase the throughput for AIMS and pattern inspection systems. The first bounce EUV collection optics are subject to harsh debris fluxes in the form of ions, neutrals and droplet fragments comprising the lifetime of the light source. Enhancing the debris mitigation reduces the reflectivity decay and therefore improves the light source cost-of-ownership (CoO). Key to optimize the debris mitigation strategy is the assessment and quantification of the detrimental plasma debris. In the present work, the high kinetic energy particles including ions and neutrals generated from the laser irradiated droplet target are resolved spatially and temporally for an intermediate pressure regime. The implications of the ion and neutral flux on the collection optics are discussed in this work. By providing fresh targets in the form of micro-meter sized droplets to the droplet irradiation position, a certain variability of the droplet position with respect to the laser focal area is inherent. By actively changing the droplet position with respect to the laser focal area with a control system the influence on ion and EUV propagation direction is studied in this work. Finally, the long term LPP source operation is assessed. The debris mitigation system is enhanced employing a three-layer strategy demonstrating an increased source cleanliness for a GI collector configuration. Results from a sample exposure test for EUV reflection degradation of the first collector optics and the impact on the CoO will be presented.