X-Ray Testing of Supersmooth Surfaces
Development of Methods and Instrumentation for the X-Ray Testing of Supersmooth Surfaces and Interfaces
Tech Area / Field
- INS-MEA/Measuring Instruments/Instrumentation
8 Project completed
Senior Project Manager
Bunyatov K S
FIAN Lebedev, Russia, Moscow
- VNIITF, Russia, Chelyabinsk reg., Snezhinsk
- Lawrence Livermore National Laboratory, USA, CA, Livermore\nEuropean Synchrotron Radiation Facility, France, Grenoble\nFraunhofer Institute for Applied Optics and Precision Engineering, Germany, Jena
Project summaryThe aim of the present Project is to develop and construct the X-ray equipment, measurement techniques and methods, and computer software destined to the roughness testing of supersmooth surfaces, thin films, and multilayer structures, as well as the near surface and near interface layers (transitional, diffusive, implanted, broken etc.).
Within the time of implementation of the present project there will be developed and produced:
- Automated X-ray diffractometer (0.154 nm working wavelength) of a special optimal design destined for the microroughness control;
- Automated facility for measuring the reflection and scattering of 0.5 - 15 nm soft X-ray radiation.;
- Methods of quantitative microroughness control of supersmooth surfaces, thin films, and multilayer structures;
- Adequate computer software.
The developed methods include
- development of a consistent theory of X-ray diffraction on rough reflectors, which takes into account peculiarities of the given wavelength region, that is, small radiation wavelength, small grazing angles of a probing beam, and a small variation of the dielectric constant at the interface of any two media;
- development of adequate models (basing on the experimental data) for surface, thin film, and multilayer structure, which take into account both 2D relief of the interface (roughness), and the change of the electron density of matter in the perpendicular direction (transitional, disturbed, diffusive layers, etc.) at the distance that are compatible with the X-ray wavelength;
- development and updating of the experimental techniques for studying the roughness of surfaces and interfaces;
- development of the data processing & analysis techniques.
The experimental facility, measurement techniques and software will permit one:
- to perform quantitative studies of the roughness parameters of up 0.1 nm and less, which maybe due to the unique sensitivity of X-ray methods;
- to measure the PSD function of roughness for the case of isotropic (polished) surfaces in the range of spatial frequencies from 0.05 mm-1 to 30 - 50 mm-1 (the correlation length of the roughness from 20 - 50 mm to 20 - 50 nm) without any a priori assumptions about the form of correlation function or distribution of the roughness heights; to present the surface profile in the form of the sum of independent systems of roughnesses with different rms heights and correlation lengths;
- to determine the Fourier-harmonics of the surface profile in the case of diamond-turned surfaces; to restore the surface profile when having additional information about the shape of a cutting tool; to separate the roughness, arising due to the action of the cutting tool, from the roughness arising due to vibrations of a cutting machine;
- to measure thickness of a near surface transitional layer with the sensitivity up to 0.1 nm;
- to determine the PSD functions of roughness of each of the film surfaces, as well as the spectrum of their cross-correlation function; to determine to what extent roughness of an external surface of the film is caused by the substrate roughness, or by the film deposition process;
- to determine statistical characteristics of the discontinuous films at initial stage of the growth;
- to determine thickness of thin and superthin films (1 - 500 nm) with accuracy up to 0.1 nm;
- to determine density of thin films, as well as density of matter in the near surface layer of thick samples;
- to study porous structure of the track membranes, polymer, and other films;
- to determine the PSD functions of roughness of each of the interfaces of multilayer structure, as well as the spectra of all the cross-correlation functions, basing on the general model of growth of a rough multilayer structure;
- to determine thickness of a transitional layer between neighbor interfaces of a multilayer structure (due to inter-diffusion of the layers, implantation of atoms at deposition, chemical reactions etc.) basing on the X-ray scattering and reflection measurements;
- to predict the reflection coefficient, as well as value and form of the angular distribution of scattering from multilayer mirror at the working wavelength basing on the reflection and scattering measurements at the 0.154 nm wavelength.
We expect that the X-ray facility, experimental techniques, and computer software to be developed within the framework of the present project will find applications in many problems of microelectronics, optics, X-ray optics, and high-precision machine engineering. In particular, we propose to use X-ray methods as the metrological base to advance the technique of superpolishing of glass and quarts substrates for optical and X-ray optical elements, as well to develop the technique of synthesis of short-period multilayer mirrors with ultimately high reflection coefficients at normal incidence in the range of the "water window" (l ~ 2.3 - 4.4 nm).
Potential Role of Foreign Collaborators
- Joint investigations of the microroughness of supersmooth surfaces by the use of different methods: X-ray scattering, UV scattering, atomic force microscopy, scanning tunnel microscopy and so on. Comparison of the results obtained by different methods.
- Joint investigations of the microroughness of thin films deposited by different methods.
- Joint investigations of the reflectivity and scattering of short period multilayer mirrors for X-ray region.
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