Angular and Spectral Bandwidth of Extreme UV Multilayers Near Spacer Material Absorption Edges

Abstract

High resolution imaging systems for EUV range are based on multilayer optics. Current generation of EUV lithography uses broadband Sn LPP sources, which requires broadband mirrors to fully utilize the source power. On the other hand, there always remains a possibility to use FEL or synchrotron as EUV source. FEL can produce very bright narrowband EUV light of a tunable wavelength, and the spectral bandwidth of the mirror is no longer a restriction. In this paper we look at the consequences of switching to different wavelengths if FEL source is used. For instance, it is known that the reflectance of Mo/Si multilayers increases when approaching Si Ledge , and the spectral bandwidth drops. But the behavior of an angular bandwidth (and its relation with the spectral bandwidth) is usually left out. It is also sometimes assumed that these bandwidths are correlated. For a large aperture EUV optical system with diffraction-limited resolution angular acceptance of a mirror is also a very important parameter. We show that the angular bandwidth of several multilayer systems (Mo/Si, Mo/Be, Ru/Si, Ru/B, La/B) actually increases close to spacer absorption edges, opposite to what occurs with the spectral bandwidth. We study this effect and show that it is caused by an interplay of changing optical constants of respective materials used in these multilayer combinations. We also provide an experimental check of the angular bandwidth of Mo/Si multilayers at 13.5 and 12.6 nm, which confirms our calculations.

Reflective aperiodic multilayer filters for metrology at XUV sources

“…In Fig. 1 we show on a logarithmic scale the experimental reflectivity of a single, highperformance periodic Mo/Si multilayer mirror (curve 1, [16]), normalized to its peak value at the center wavelength, λ 0 (69.8% at 13.5 nm). The reflectivity spectrum shows a bandwidth (full-width at half maximum, FWHM) of about δλ/λ = 4%.…”

“…EUV reflectivity spectra normalized to unity at 13.5 nm for direct comparison of the spectral shapes and presented in the vicinity of the Bragg peak (a) and across a wider spectral interval (b). Curve 1: experimental reflectivity spectrum of a single Mo/Si periodic multilayer mirror optimized for maximum reflectivity (68.9% [16]) at a wavelength of 13.5 nm. Curve 2: target reflectivity curve to be mimicked, calculated as the reflectivity after 12 subsequent reflections off the experimental Mo/Si mirror.…”

Carbon nanotube microfabricated window with extreme ultraviolet transmission and differential pumping

“…To increase transmission, these broadband sources require wide bandpass windows. 1 Many materials are opaque at this and lower wavelength ranges, 2 which makes developing a wide bandpass window difficult. Windowless transitions between chambers have been practiced for hard x-rays for several years.…”

Influence of Pre-Ionized Plasma on the Dynamics of a Tin Laser-Triggered Discharge-Plasma

“…At present, the 13.5 nm extreme ultraviolet lithography (EUVL) is one of the photolithography methods with the most potential [1]. The wavelength is 13.5 nm emission in a 2% bandwidth, which is mainly for the molybdenum-silicon (Mo/Si) multilayer mirrors [2] and the photo resistance [3]. Due to the high convention efficiency of 13.5 nm emission, Sn has been widely used as an extreme ultraviolet (EUV) source [4].…”