19 March 2015 LPP light source for actinic HVM inspection applications
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EUV sources with high brightness and stability are required for actinic photomask inspection. High availability and cleanliness after IF are additional stringent requirements. EUV lithography is only production ready, if these tools are available with HVM specifications. At the Laboratory for Energy Conversion, ETH Zurich, droplet-based EUV LPP sources have been designed, developed and tested at the system level for the last 8 years and has been commercialized by Adlyte AG. The most advanced facility, namely ALPS II, has been operated as a prototype source for hundreds of hours. In the present work, the EUV plasma is imaged with the help of a pinhole camera. The dimension of the plasma in the direction of the laser axis and the direction of the train equal 60 μm and 70 μm, respectively. The plasma is also imaged using an ICCD with an exposure time of 5 ns. The observed droplet plasma has a characteristic kidney shape. The ICCD is a valuable diagnostic as inspection tools require high pulse-to-pulse reproducibility that cannot be assessed to the full extend using a EUV pinhole camera. Various collector configurations, using either NI or GI, have been integrated into the source. The measurements of the emission characteristics at IF for a GI collector configuration reveal a Gaussian spot shape at IF and a pulse-to-pulse stability of 6.8 % (σ), which matches previous stabilities at the source level. The debris mitigation system employs a three layer strategy between the plasma and IF. Introducing a high momentum flow as a first layer of debris mitigation, the load of tin spots on the collector could be reduced by a factor of 9, hence a significant increase of source life-time is obtained. A quantification by Adlyte of IF cleanliness after 24 hours source operation revealed no relevant contamination with respect to the requirements for Blank Inspection Cleanliness after IF.
© (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Bob Rollinger, Bob Rollinger, Nadia Gambino, Nadia Gambino, Duane Hudgins, Duane Hudgins, Alexander Sanders, Alexander Sanders, Markus Brandstätter, Markus Brandstätter, Reza S. Abhari, Reza S. Abhari, F. Abreau, F. Abreau, "LPP light source for actinic HVM inspection applications", Proc. SPIE 9422, Extreme Ultraviolet (EUV) Lithography VI, 94222K (19 March 2015); doi: 10.1117/12.2085794; https://doi.org/10.1117/12.2085794

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