Pierre Boher

A transmission electron microscopy study of low‐temperature reaction at the Co‐Si interface

An efficient preparation method, which provides wedge‐shaped cross‐section transmission electron microscopy samples, has been developed. It was then used to investigate the structure of as‐deposited cobalt multilayers on silicon substrates by rf plasma sputtering. It was found that an extended reaction takes place between Co and Si probably during the deposition. The cobalt atoms react with the silicon substrate to form an amorphous silicide layer. When the deposited layer is <3 nm thick, it entirely reacts with the substrate and can form an amorphous silicide as large as 5 nm. Above 4–5 nm thickness, growth of Co crystallites comes in competition with the formation of the amorphous silicide and limits it to 2 nm. The composition of this amorphous silicide is estimated to be Co2Si. In Co/C multilayers, the reactivity between the two materials is negligible, and the coalescence thickness of cobalt is 2–3 nm. At 2 nm, the cobalt layers are noncontinuous and very rough, whereas at 3 nm the critical thickness...

Grazing x-ray reflection analysis of nanometric scale structures

Grazing x‐ray reflection (GXR) has been performed on thick WN layers and on C/W multilayer mirrors deposited in a diode rf‐sputtering system. In the first case, we show that GXR can provide not only the layer thickness but also precise information on the occurrence of intermediate layers (native oxide superlayer, reactionlike sublayer). The relative thickness of each layer is determined very precisely. The GXR analysis of C/W multilayers can be perfectly interpreted using a physical model which includes a thickness drift during the deposit, an interface layer between W and C layers due to the interdiffusion, and interface roughness. In each case, the GXR simulation models are confirmed by in situ kinetic ellipsometry and ex situ transmission electron microscopy. Moreover, in the W/C multilayer case the soft x‐ray reflectivity calculated at the CKα line assuming the same model agree very well with the experimental value.

A new way to characterize autostereoscopic 3D displays using Fourier optics instrument

Auto-stereoscopic 3D displays offer presently the most attractive solution for entertainment and media consumption. Despite many studies devoted to this type of technology, efficient characterization methods are still missing. We present here an innovative optical method based on high angular resolution viewing angle measurements with Fourier optics instrument. This type of instrument allows measuring the full viewing angle aperture of the display very rapidly and accurately. The system used in the study presents a very high angular resolution below 0.04 degree which is mandatory for this type of characterization. We can predict from the luminance or color viewing angle measurements of the different views of the 3D display what will be seen by an observer at any position in front of the display. Quality criteria are derived both for 3D and standard properties at any observer position and Qualified Stereo Viewing Space (QSVS) is determined. The use of viewing angle measurements at different locations on the display surface during the observer computation gives more realistic estimation of QSVS and ensures its validity for the entire display surface. Optimum viewing position, viewing freedom, color shifts and standard parameters are also quantified. Simulation of the moire issues can be made leading to a better understanding of their origin.

Magnetic and structural properties of rf‐sputtered Co/Fe and Co/Cr multilayers

Multilayers alternating cobalt with different spacers such as iron and chromium at nanometric scale have been deposited by rf diode sputtering. The structures have been characterized in situ by kinetic ellipsometry and ex situ by grazing x‐ray reflection, x‐ray diffraction, Auger profile analysis, and transmission electron microscopy. Nuclear magnetic resonance (NMR) and high‐field SQUID magnetometry have been used to determine the magnetic properties. In Co/Fe multilayers the structure strongly depends on the cobalt thickness tCo. For tCo below 2 nm, the cobalt layers exhibit a bcc crystalline structure, and the crystalline coherence extends over many periods. For tCo above 2 nm, for Co a mixed fcc‐hcp phase has been observed. In this case the crystalline coherence is destroyed from one iron layer to the other. The NMR frequency (198 MHz), and the magnetic moment (1.58 μB/atom) of bcc cobalt have been evaluated. A similar behavior is observed in Co/Cr multilayers, the bcc phase disappearing around tCo=1....

Multispectral polarization viewing angle analysis of circular polarized stereoscopic 3D displays

In this paper we propose a method to characterize polarization based stereoscopic 3D displays using multispectral Fourier optics viewing angle measurements. Full polarization analysis of the light emitted by the display in the full viewing cone is made at 31 wavelengths in the visible range. Vertical modulation of the polarization state is observed and explained by the position of the phase shift filter into the display structure. In addition, strong spectral dependence of the ellipticity and polarization degree is observed. These features come from the strong spectral dependence of the phase shift film and introduce some imperfections (color shifts and reduced contrast). Using the measured transmission properties of the two glasses filters, the resulting luminance across each filter is computed for left and right eye views. Monocular contrast for each eye and binocular contrasts are performed in the observer space, and Qualified Monocular and Binocular Viewing Spaces (QMVS and QBVS) can be deduced in the same way as auto-stereoscopic 3D displays allowing direct comparison of the performances.

Tb/Fe multilayers : a study by conversion electron Mössbauer spectrometry and polar Kerr effect

Abstract Sputtered Tb/Fe multilayers (ρ Tb =0.2–1.9 nm, ρ Fe = 0.2–3.3 nm) have been characterized both by CEMS and the Kerr effect. Saturated Kerr angles υ K vary linearly with the hyperfine field at the iron site, indicating the υ K comes mainly from the iron magnetic moment. All the structural and magnetic results can be interpreted in a (ρ Tb ,ρ Fe ) diagram.

Structural and magnetic properties of diode radio‐frequency sputtered Cr/Co multilayers

Structural properties of diode radio‐frequency (rf)‐sputtered Cr/Co multilayers have been investigated using in situ kinetic ellipsometry, grazing x‐ray reflection, x‐ray diffraction, and nuclear magnetic resonance. Results have been correlated with magnetic characterizations obtained by SQUID susceptometry. Interdiffusion along ≂10 A occurs at the ‘‘Cr on Co’’ interface. The Co on Cr interface appears sharper. X‐ray diffraction and nuclear magnetic resonance show that Co layers grow with bcc structure when the Co layer thickness dCo is lower than ≂15 A. In this case, the films are strongly textured with the Cr bcc (100) direction perpendicular to the plane of the substrate. A better structural coherence is observed for the thinner layers. When dCo is thicker than ≂15 A, a mixture of hcp and fcc Co phases appears by x‐ray diffraction and nuclear magnetic resonance. The good structural quality of the films is confirmed by the occurrence of satellite peaks in the x‐ray diffraction patterns. The Co magnetic ...

Silicon/silicon oxide and silicon/silicon nitride multilayers for extreme ultraviolet

Si/SiO2 and Si/Si3N4 multilayers have been fabricated using a locally made reactive diode ri-sputtering system. The layer alternation is obtained by modulating a partial pressure of oxygen or nitrogen near the sample using a silicon target with argon as sputtering gas. O2 and N2 partial pressure conditions were optimized to deposit stoichiometric SiO2 and Si3N4 films without significant reaction with the silicon target. In situ kinetic ellipsometry was used to monitor both thick film and multilayer deposition. The different interfaces appear very sharp with a little contamination of the silicon layers especially using oxygen. The multilayers were characterized by grazing x-ray reflection (Cu-K α line), and the reflectivity was measured in the soft x-ray range (120-350 A) by synchrotron radiation. Both Si/SiO2 and Si/Si3N4 multilayers exhibit well-defined Bragg peaks with very narrow bandpasses (two to three times lower than the conventional Mo/Si multilayer), and high absolute reflectivities (up to ≅22% at 130 A). Finally, thermal stability of Si/Si3N4 multilayers was evaluated. We did not find any degradation after annealing up to 800°C, which is extremely high compared to conventional Mo/Si multilayers, which are generally destroyed above 500°C.

Structural and magneto‐optical properties of Tb/Fe and (Tb/Fe)/Si3N4 multilayers

Tb/Fe and (Tb/Fe)/Si3N4 multilayer films with layers in the nanometric range have been prepared using a reactive diode rf sputtering system. Their structural and magneto‐optical properties have been investigated to determine the stack parameters, the crystallization states, the direction of easy magnetization, and the Kerr angle values. The multilayer structure can be observed even when terbium layers are about 0.2 nm thick. Iron crystallization appears to depend on the terbium layer thickness. For Tb layer thicknesses greater than 0.37 nm, iron is amorphous when thinner than 3 nm. It spontaneously crystallizes when the layer becomes thicker. When Tb layer thickness is smaller than 0.37 nm, Fe crystallization is always detected: It occurs in the whole stack through the incomplete Tb layers. Kerr rotation measurements show a magnetic anisotropy depending on the Tb/Fe thickness ratio. Indeed, the direction of easy magnetization was found to be in the plane of the samples for ratio values of about 0.23 and 1...

Structural and electrical properties of silicon nitride films prepared by multipolar plasma‐enhanced deposition

A new system of dielectric deposition using a multipolar plasma enhanced by a hot filament has been used to deposit multipolar plasma chemical vapor deposition silicon nitride films on various substrates (GaAs, Si, GaInAs, etc.). Using in situ kinetic ellipsometry during the depositions, the flow ratio SiH4/N2 has been optimized to form as dense silicon nitride as possible. The density variation has been attributed to a variable amount of oxygen in the films certainly in the form of silicon dioxide. Using Rutherford backscattering and spectroscopic ellipsometry, the amounts of oxygen have been measured precisely. Using infrared absorption, we have demonstrated the low hydrogen concentration of our films compared to plasma‐enhanced chemical vapor deposition ones. At constant flow ratio, we have demonstrated the effect of the deposition rate on the stoichiometry of the films. Films deposited at very low deposition rates (<10 A/min) are quasistoichiometric and produce important reductions of GaInAs/Si3N4 int...