Surface and interface roughness estimations by X‐ray reflectivity and RBS measurements

X-ray reflectivity study on TiN/Ti/Si structures before and after annealing

Approximately 1.8 µm thick nanolayered multilayer coatings of TiN/CrN (also known as superlattices) were deposited on silicon (1 0 0) substrates at different modulation wavelengths (4.6–12.8 nm), substrate temperatures (50–400 °C) and substrate bias voltages (−50 to −200 V) using a reactive direct current magnetron sputtering system. The x-ray reflectivity (XRR) technique was employed to determine various properties of the multilayers such as interface roughness, surface roughness, electron density, critical angle and individual layer thicknesses. The modulation wavelengths of the TiN/CrN superlattice coatings were calculated using a modified Bragg's law. Furthermore, the experimental XRR patterns were simulated using theoretically generated patterns and a good fit was obtained for a three layer model, i.e. (1) top surface roughness layer, (2) TiN/CrN multilayer coating (approximately 1.8 µm) and (3) Ti interlayer (∼0.5 µm) at the film–substrate interface. For the superlattice coatings prepared at a modulation wavelength of 9.7 nm, a substrate bias of −200 V and a substrate temperature of 400 °C the XRR patterns showed Bragg reflections up to 5th order, indicating well-defined periodicity of the constituent layers and relatively sharp interfaces. The simulation showed that the superlattice coatings prepared under the above conditions exhibited low surface and interface roughnesses. We also present the effect of substrate temperature and substrate bias, which are critical parameters for controlling the superlattice properties, onto the various interface properties of TiN/CrN superlattices.

Simulation of RBS spectra with known 3D sample surface roughness

Combining grazing incidence X-ray diffraction and X-ray reflectivity for the evaluation of the structural evolution of HfO 2 thin films with annealing

The influence of surface and interface roughness on X-ray and extreme ultraviolet (EUV) reflectometry is becoming increasingly important as layer thicknesses decrease to a few nanometers in next-generation nanodevices and multilayer optics. Here we simulate two different approaches for numerically modeling roughness, the Névot–Croce factor and the graded-interface method, in the Parratt formalism of calculating the complex reflectance of multilayer systems. The simulations were carried out at wavelengths relevant to widely used metrology techniques, including 0.154 nm for X-ray reflectometry and 13.5 nm for EUV lithography. A large discrepancy is observed between the two approaches in several situations: when the roughness is large with respect to the wavelength, for interfaces with large changes in refractive index across the boundary, as well as around reflectance peaks due to interference effects. Caution is thus required when using either approach to model roughness in these situations.

Effect of swift heavy ion irradiation in W/Co multilayer structures

Dependence of structural features on substrates in Co/Cu multilayers

The Exchange Bias (EB) effect is observed at the interface of Antiferromagnet/Ferromagnet (AF/FM) structures and depends on the interface roughness (IR). Until today, only low IR values, usually below 10 nm, have been investigated. Here we investigate an extended range of IR through controlling the surface roughness (SR) of the employed substrates. We employ CoO/Co bilayers (thickness within 10-60 nm), a classic AF/FM structure that exhibits intense EB. ZnO was employed as the substrate in both film and bulk forms, enabling us to vary the SR up to 840 nm. Our data reveal a strong relative decrease, ranging within 20-65%, of both the shift Hshift EB and coercive Hc EB fields upon increase of SR (IR), for both parallel and normal magnetic field-sample configurations. For the explanation of these findings we propose that in thin AF/FM structures deposited on rough substrates the local magnetization, Mf of the FM is ‘locked’ mainly in-layer due to shape anisotropy, thus it is forced to follow the morphologically rough landscape of the substrate. This imposes misalignment between Mf , that is ‘directionally random’, and Hex , that is ‘directionally oriented’. This weakens the biasing potential of Hex on Mf and reduces the relative macroscopic parameters Hshift EB amd Hc EB .

Comprehensive X-ray reflectivity (XR) studies were conducted to characterize the structure of thin polyalkylsilicate films made of a poly(methylsilsesquioxane-co-ethylenylsilsesquioxane) precursor containing a star-shaped poly(ε-caprolactone) as a pore generator (porogen). The films were deposited on silicon wafer substrates by spin-coating and subsequently cured at various temperatures. Such spin-on glasses have a potential application as a low-dielectric-constant material for advanced semiconductors. Because high-intensity synchrotron X-ray radiation was used, the XR data could be measured over 9 orders of magnitude in intensity, which facilitated the observation of fine structural details. A hierarchical fitting procedure for modeling the XR data is given. By evaluation of the critical angle of total reflection of the film material, which was observed at smallest angles, in particular the film electron density could be determined with a high accuracy. The films cured at 420 °C show a lower electron density as compared to those cured at 250 °C. This is explained by the fact that at the higher temperature the porogen is calcined and escapes from the films leaving behind a nanoporous structure. Film porosities could be estimated from the observed changes in the electron densities. From the very large number of high-frequency oscillations observed in the XR curves, it is concluded that the films exhibit a homogeneous, well-defined structure with small interface and surface roughness. The film thickness could be determined with an accuracy of ±1 Å. The observation of an additional low-frequency modulation of the XR curves revealed a surface skin layer with a thickness of ca. 45 Å and with a slightly increased electron density as compared to the bulk of the film.

Investigation into the interfacial stiffness ratio of stationary contacts between rough surfaces using an equivalent thin layer

Comparative study on wetting of smooth and rough silica surface by molten Sn–3.5Ag–2Ti alloys

The lateral-periodicities of the surface and interfacial roughnesses of a multilayer- Bragg reflector which affect x-ray reflectivity have been examined using the x-ray rocking curve profile measurements and a stylus surface profilometer. Multilayered films have been fabricated by a proprietary sputtering technique. The x-ray rocking curve profiles of the first Bragg reflection of the multilayered films have been examined with a precision x-ray diffractometer. These profiles show that the lateral-periodicity of the film surface and interfacial roughness which primarily affect the CuKa X-ray reflectivity is about 4 rim. The measured CuKa x-ray reflectivity of the multilayered film is in good agreement with calculations which incorporate the estimated film surface and interfacial roughness. 1.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Paper 962804

Wide-band electromagnetic scattering from multiple objects shallowly buried beneath rough earth soil surfaces has been an important research topic in recent years because of its extensive applications in detecting the buried objects such as mines, pipes, and tunnels. Due to the advantages of finite-difference time-domain (FDTD) method in simulating wide-band electromagnetic scattering from rough surface in the presence of multiple objects, the FDTD method under Gaussian differential pulse wave incidence is utilized in the present study to analyze the frequency response of rough soil surfaces with shallowly buried objects, which serves as a basis for the detection and discrimination of objects buried below rough soil surfaces. The Topp equation model that can predict the dielectric constant of soil-water mixture is adopted in the present study to properly describe the dielectric property of earth soil with water. The actual rough land surface is modeled as the realization of a Gaussian random process with exponential spectrum by using Monte Carlo method. Simulation results show that the variation of composite scattering coefficient with frequency is oscillatory. It is also shown that the composite scattering coefficient versus frequency increases with the increase of root-mean-square of soil surface, water ratio of soil, the target section height, and the separation distance of target. However, simulation results indicate that the composite scattering coefficient versus frequency decreases with the increase of target section width. In summary, the variation of wide-band scattering coefficient is very complicated and is very sensitive to the incidence angle of electromagnetic wave. However, the wide-band scattering coefficient under Gaussian differential pulse wave incidence is less sensitive to the correlation length of rough soil surface, the depth of buried objects, and the dielectric constant of target. These qualitative results relating to the frequency response of rough soil surfaces in the presence of multiple objects are potentially valuable for detecting and discriminating the objects buried below rough soil surfaces by utilizing a wide-band ground penetrating radar system, although the present study is limited to one-dimensional rough soil surface due to the severe computational burden encountered in the large-scale Monte Carlo simulations. In addition, compared with frequency-domain numerical methods, the FDTD method has significant advantages in calculating wide-band composite scattering from rough surfaces in the presence of multiple objects, and thus has extensive applications in radar imaging simulation of multiple objects below or above rough surfaces, which goes beyond the scope of this paper.

Recent advances in characterization of ultra-thin films using specular X-ray reflectivity technique