High-Temperature LPP Collector Mirror

摘要

The EUV source output power and the collector optics lifetime have been identified as critical key issues for EUV lithography. In order to meet these requirements a heated collector concept was realized for the first time. An ellipsoidal collector substrate with an outer diameter of 320 mm was coated with a laterally graded high-temperature multilayer. The interface-engineered Mo/Si multilayer coating was optimized in terms of high peak reflectivity at 13.5 nm and a working temperature of 400°C. Barrier layers were introduced on both interfaces to block thermally induced interdiffusion processes of molybdenum and silicon to provide long-term optical stability of the multilayer at elevated temperatures. A normal-incidence reflectance of more than 40% at 13.55 nm was measured after heating. After initial annealing at 400°C for one hour, no degradation of the optical properties of these multilayer coatings occurred during both long-term heating tests for up to 100 hours and multiple annealing cycles. The successful realization of this high-temperature sub-aperture collector mirror represents a major step towards the implementation of the heated collector concept and illustrates the great potential of high-temperature EUV multilayer coatings.