Enhanced reflectivity and stability of high-temperature LPP collector mirrors

Abstract

The source output power and lifetime, including the collector optics lifetime, are among the key issues for EUV lithography systems. In order to meet the requirements for the EUV collector mirror, both the reflectivity and the long-term thermal stability of its multilayer coating have been enhanced considerably during recent development efforts. Sub-aperture ellipsoidal mirrors of different substrate materials with outer diameters of about 320 mm were coated with laterally graded high-temperature multilayers. The interface-engineered Mo/Si multilayer mirror (MLM) coatings were optimized in terms of high peak reflectivity at 13.5 nm and working temperatures above 400°C. Thin barrier layers were introduced on both interfaces to block thermally induced interdiffusion processes of molybdenum and silicon and to provide long-term optical stability of the coating at elevated temperatures. A normal-incidence reflectance of R ~ 60 % at 13.5 nm was measured on Si wafer samples after heating up to 600°C. No degradation of the optical properties of these multilayer coatings occurred during both long-term heating tests and multiple annealing cycles. On highly polished collector substrates with improved surface roughness a reflectance for s-polarized light exceeding peak values of R = 57 % was obtained. With optimized layer gradient the degree of wavelength matching was improved, as well, resulting in peak reflectivity values above 56 % throughout the clear aperture for a series of measurement points across the mirror. The corresponding area-weighted 2% in-band average reflectance for this collector mirror coating exceeds 52 % for unpolarized light

DLC/Si multilayer mirrors for EUV radiation

“…Especially for the collector mirror, which is the closest part next to the hot plasma, temperature stable multilayers and chemical robust surface coatings are essential. For example the typical temperature of the mirror surface of a collector shell in recent HVM lithography tools is around 400 °C [16].…”

Toward spatial and spectral control of waveguided high-harmonic generation

“…The LPP radiation is spontaneous and emitted in 2 solid angle where collecting the radiation is difficult and optics can be contaminated with ablated material. However many promising efforts have been undertaken to solve these issues [18][19][20][21].…”

“…The HH output for a range of harmonics (q =13,15,17,19,21,23,25,27,29) and the summation (total) of harmonics as a function of drive laser pulse energy, E p . The inset shows an enlarged view for the HH output of harmonics ranging from 13 th to 23 rd .…”