Search

For several years Sagem has invested in technologies and engineering to develop innovative solutions for collecting optics for LPP and DPP EUV sources. Among the technological challenges for collecting mirrors, thermal control plays a very important role in avoiding degradation of in band EUV reflectivity and maintaining far field optical performance during scanner operation. Sagem proposes solutions based on a metallic mirror with embedded cooling circuits to stabilize the temperature of the mirror during source operation. Results of simulation as well as first technology validations obtained on prototypes will be shown to demonstrate the performance of the cooled mirror design. Another critical performance about the collector is the HSFR (micro roughness) requirements of the optical surface for limiting scattering and optimizing the in band EUV reflectivity. Thanks to the specific polishing process, HSFR values of below 2 Angstroms have been achieved on demonstrator metallic mirrors with high departure aspheres. Reflectivity measurements performed after coating of these parts with MoSi multilayers confirm that the obtained polishing quality is compliant with polishing specifications for high performance EUV optics. Finally, upcoming developments at Sagem in the field of EUV collecting optics will be presented.

Through its participation to European programs, SAGEM has worked on the design and manufacturing of normal incidence collectors for EUV sources. By opposition to grazing incidence, normal incidence collectors are expected to collect more light with a simpler and cheaper design. Designs are presented for the two current types of existing sources: Discharge Produced Plasma (DPP) and Laser Produced Plasma (LPP). Collection efficiency is calculated in both cases. It is shown that these collectors can achieve about 10 % efficiency for DPP sources and 40 % for LPP sources. SAGEM works on the collectors manufacturability are also presented, including polishing, coating and cooling. The feasibility of polishing has been demonstrated with a roughness better than 2 angstroms obtained on several materials (glass, silicon, Silicon Carbide, metals...). SAGEM is currently working with the Institut d'Optique and the Laboratoire des Materiaux Avances on the design and the process of EUV coatings for large mirrors. Lastly, SAGEM has studied the design and feasibility of an efficient thermal control, based on a liquid cooling through slim channels machined close to the optical surface.