The laser system is by far the most expensive part of a laser-produced plasma (LPP) EUV source. Thus LPP source designers have not only to optimize the technical performances of the lasers but also cost, efficiency, reliability, redundancy and industrial availability of their approach. Based on the typical conversion efficiencies of present LPP source targets (CE ~ 1- 3%), the laser system will have to deliver an average power of at least 20 kW. This can hardly be obtained with only few laser chains. Starting from this consideration, the EXULITE consortium has first proposed the concept of a spatially multiplexed and modular LPP source using 10 to 20 identical, moderate power laser units which are simultaneously focused on the same spot. This approach increases system redundancy and reduces the development cost of the laser. We will present an original technical approach which allows both to manage the multi-beam attack of the target using a closed-loop control and to collect a maximum of EUV power. The grazing incidence EUV collector is designed such that optimized vacuum pumping and debris mitigation can be obtained. Finally, we can show that modular LPP sources can satisfy the severe EUV dose stability that is commonly requested.
Within the PREUVE project, the GAP of CEA Saclay has developed an EUV source that should meet (alpha) -tool specifications by the end of this year. In particular, a laser-produced plasma source has been developed that uses a dense and confined xenon jet target. Our technical solution is based on a specific target injector design and the use of well adapted nozzle materials to avoid debris formation by plasma erosion. After injection, the xenon is recycled and highly purified to reach a low cost round- the-clock operation. This source provides both high conversion efficiency and low debris flux. These are necessary conditions for its industrial application in the future EUV microlithography. The conception of the so-called ELSA (EUV Lithography Source Apparatus) prototype allows in principal 2 years full operation on the French lithography test bench BEL (Banc d'essai pour la lithographie) that has been developed during PREUVE. In parallel, the EXULITE consortium that is coordinated by Alcatel Vacuum Technology France (AVTF) has started its activities in the frame of the European MEDEA+ initiative on EUV source development. In collaboration with Thales and the CEA, AVTF develops a prototype power source for EUV lithography production tools by the end of 2004. A low cost and modular high power laser system architecture has been chosen and is developed by Thales and the CEA to pump the laser plasma- produced EUV source.
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