Wavelength separation from extreme ultraviolet mirrors using phaseshift reflection

A generic design and fabrication scheme of Mo/Si multilayer-grating phaseshift reflector systems is reported. Close to optimized extreme ultraviolet (EUV, λ=13.5  nm ) reflectance values up to 64% are demonstrated, while the diffractive properties can be exploited in spectral filtering applications. The results can contribute to a wavelength-unspecific solution for the suppression of λ>100  nm out-of-band radiation in EUV lithography

Surface morphology of Kr+-polished amorphous Si layers

The surface morphology of low-energy Kr+-polished amorphous Si layers is studied by topographical methods as a function of initial substrate roughness. An analysis in terms of power spectral densities reveals that for spatial frequencies 2×10−2–2×10−3 nm−1, the layers that are deposited and subsequently ion polished reduce the initial substrate roughness to a rms value of 0.1 nm at the surface. In this system, the observed dominant term in linear surface relaxation, proportional to the spatial frequency, is likely to be caused by the combined processes of (a) ion-induced viscous flow and (b) annihilation of (subsurface) free volume during the ion-polishing treatment. Correspondingly, a modification of the generally assumed boundary conditions, which imply strict surface confinement of the ion-induced viscous flow mechanism, is proposed. Data on surface morphology are in agreement with the optical response in extreme ultraviolet from a full Mo/Si multilayered system deposited onto the modified substrate

Influence of noble gas ion polishing species on extreme ultraviolet mirrors

Low energy ion polishing is attractive in thin films because of the small interaction zone with the treated material. In this context, various noble gases (Ne, Ar, Kr, and Xe) have been applied for low energy ion polishing of interfaces in nanoscale optical Mo/Si multilayers in order to mitigate the evolving roughness during the deposition process. The interface morphology has been studied by grazing incidence small angle x-ray scattering, the multilayer composition by x-ray photoelectron spectroscopy, and the general performance by extreme ultraviolet (EUV) reflectometry. Both the average roughness level and the vertical correlation length of the roughness can be reduced significantly by increasing the atomic mass of the ion species applied for polishing. Maximum EUV reflectance is observed for Krþ-polishing, while Xeþ-polishing shows a superior structure. This apparent contradiction is explained by taking into account the optical absorption from noble gas residuals in the amorphous silicon layers

EUV-multilayers on grating-like topographies

In this study, multilayer morphology near the key anomalies in grating-like structures, namely sharp step-edges and steep walls, are examined. Different deposition schemes are employed. Based on cross section TEM analysis an explanatory model describing the morphology of the successive layers is developed. A further insight into the periodicity and the general performance of the multilayer is obtained by EUV microscopy. The main distortions in multilayer structure and hence EUV performance are found to be restricted to a region within a few hundred nanometers from the anomalies, which is very small compared to the proposed grating period (50-100 μm). These multilayer coated blazed gratings can thus be considered a viable option for spectral purity enhancement of EUV light source

Extreme Ultraviolet Bragg mirrors with suppressed infrared reflectivity properties

Many optical applications demand high reflectivity in a particular wavelength range while simultaneously requiring suppression of radiation outside this range. Such parasitic radiation can for instance lead to image distortions in imaging applications or poor signal-noise ratios in spectroscopy. The most obvious need for radiation with high “spectral purity” can be found in extreme UV lithography (EUVL). EUVL utilizes narrow-band (13.5 nm ± 1%) radiation being extracted from a broad-band spectrum emitted by dense hot plasma sources. For this purpose we proposed and investigated various methods to integrate EUV reflecting multilayers with resonant infrared anti-reflecting structures. We discuss our pilot experiments, physics and optical properties of the realized structures in broad spectral range – from the EUV up to the infrared ranges