Table-top reflectometer in the extreme ultraviolet for surface sensitive analysis

Abstract

We suggest a reflectometer for thin film analysis based on a plasma-discharge source utilizing extreme ultraviolet (XUV) radiation in a wavelength region of 4–40 nm. In contrast to other laboratory based reflectometers, which are designed for the near normal incidence case to characterize XUV multilayer optics and maskblanks, in our approach we move to a selectable fixed grazing incidence angle that enables surface sensitive analysis of almost arbitrary ultrathin film systems providing high elemental contrast due to the characteristic absorption of XUV by matter. Most materials (e.g., Si, Al, Gd, and Ag) exhibit characteristic absorption edges allowing not only to determine layer thicknesses, surface or interlayer roughnesses in a stack, but also elemental composition and even analyzing the absorption fine structures. Together with our simulations we show that our polychromatic approach makes it possible to provide all these parameters in one measurement.

Radiation characteristics of extreme UV and soft X-ray sources

“…Surface analysis becomes extremely precise by means of reflectometry and scatterometry [4,5,6] and also the binding state of molecules can be studied by spectral investigations [7,8,9]. Microscopy with radiation at wavelengths in the water window (λ = 2.3 .…”

Multi‐angle spectroscopic extreme ultraviolet reflectometry for analysis of thin films and interfaces

“…The measurement uncertainty of the method is at the same level as discussed for single-angle system previously [7,17]. Additional uncertainty here can arise from angular misalighnment errors of the deflection mirror but the total uncertainty budget is not expected to exceed 2% in the available range of wavelengths and incidence angles.…”

“…1). It is a development of previously presented singleangle EUV reflectometer [11], which is now able to measure reflectivity on grazing incidence angles between 2° and 15°. The principal scheme of the tool is shown in Fig.…”

“…Depending on the used gas or gas mixture, the EUV source can produce light in the whole EUV wavelength region between 5 nm and 40 nm. For spectroscopic reflectometry quasi-continuous spectra from heavy gases, such as xenon, are preferable, enabling single pulse measurements of reflectivity in the wavelength range between 10.5 nm and 16 nm [7,11]. To extend this range an optimised krypton/xenon mixture was utilised to produce quasi continuous spectra in the region between 9.5 nm and 17 nm (see Fig.…”

“…One of the most promising methods is spectroscopic reflectometry in extreme ultraviolet (EUV) wavelength range [7]. Developed previously with synchrotrons as the radiation sources [8], the method is currently under development with laboratory plasma-based EUV sources [9,10] which should enable its widespread application [11]. In this contribution we are reporting the experimental realisation of a multi-angle spectroscopic reflectometer that is able to measure reflectivity in the wavelength region between 9 nm and 17 nm and with grazing illumination angles between 2° and 15°.…”