High reflectance multilayers for EUVL HVM-projection optics

Reported is a summary of multilayer deposition results by FOM on three elements of the projection optics of the ASML Extreme UV Lithography HVM tools (1). The coating process used is e-beam evaporation in combination with low-energy ion-beam smoothening. The reflectance of the coatings, which are covered with a special protective capping layer, is typically around 68%, with a maximum value of 69.6% and a non-correctable figure error added by the full multilayer stack of better than 35 picometer. The results are compared to the earlier coatings of the EUVL Process Development Tool (2).