In situ and real-time monitoring of structure formation during non-reactive sputter deposition of lanthanum and reactive sputter deposition of lanthanum nitride

Lanthanum and lanthanum nitride thin films were deposited by magnetron sputtering onto silicon wafers covered by natural oxide. In situ and real-time synchrotron radiation experiments during deposition reveal that lanthanum crystallizes in the face-centred cubic bulk phase. Lanthanum nitride, however, does not form the expected NaCl structure but crystallizes in the theoretically predicted metastable wurtzite and zincblende phases, whereas post-growth nitridation results in zincblende LaN. During deposition of the initial 2-3 nm, amorphous or disordered films with very small crystallites form, while the surface becomes smoother. At larger thicknesses, the La and LaN crystallites are preferentially oriented with the close-packed lattice planes parallel to the substrate surface. For LaN, the onset of texture formation coincides with a sudden increase in roughness. For La, the smoothing process continues even during crystal formation, up to a thickness of about 6 nm. This different growth behaviour is probably related to the lower mobility of the nitride compared with the metal. It is likely that the characteristic void structure of nitride thin films, and the similarity between the crystal structures of wurtzite LaN and La2O3, evoke the different degradation behaviours of La/B and LaN/B multilayer mirrors for off-normal incidence at 6.x nm wavelength

The effect of W thickness on the interface Si-on-W, a Low-Energy Ion Scattering study

X-ray optics is based on reflective multilayers with layer thicknesses of a few nanometers at most. The interface quality plays a central role in determining the final properties of these structures. However, the accurate characterization of such interfaces with the necessary quasi-atomic resolution is still a challenge. For this reason, we typically combine several characterization methods, such as X-ray reflectivity (XRR), X-rays photoelectron spectroscopy (XPS), ion scattering spectroscopy and Transmission Electron Microscopy (TEM), to get complementary information regarding the interface profiles. Here we investigated the resolution of Low-Energy Ion Scattering (LEIS) to characterize buried interfaces. The aim is to build a new approach to characterize interface profiles and provide complementary information to XRR and XPS.We investigated a strategy to assist spectra analysis with simulations and developed a method to quantify the effective width of interfaces from the tails of LEIS spectra.The resolution of LEIS tails proved to be higher than expected for interfaces that are buried less than 2nm from the surface. The method that we designed tested accurate and precise when compared to TEM measurements, with a precision of 0.1 nm.With this approach, we measured the effective width of Si-on-W interfaces and we were able to resolve a 0.1 nm difference in the effective interface width caused by different W thicknesses

Influence of the Template Layer on the Structure and Ferroelectric Properties of PbZr0.52Ti0.48O3Films

The microstructure of the PbZr0.52Ti0.48O3(PZT) films is known to influence the ferroelectric properties, but so far mainly the effect of the deposition conditions of the PZT has been investigated. To our knowledge, the influence of the underlying electrode layer and the mechanisms leading to changes in the PZT microstructure have not been explored. Using LaNiO3(LNO) as the bottom electrode material, we investigated the evolution of the PZT microstructure and ferroelectric properties for changing LNO pulsed-laser deposition conditions. The explored deposition conditions were the O2pressure, total pressure, and thickness of the electrode layer. Increasing both the O2pressure and the thickness of the electrode layer changes the growth of PZT from a smooth, dense film to a rough, columnar film. We explain the origin of the change in PZT microstructure as the increased roughness of the electrode layer in relaxing the misfit strain. The strain relaxation mechanism is evidenced by the increase in the crystal phase with bulk LNO unit cell dimensions in comparison to the crystal phase with substrate-clamped unit cell dimensions. We explain the change from a dense to a columnar microstructure as a result of the change in the growth mode from Frank-van der Merwe to Stranski-Krastanov. The ferroelectric properties of the columnar films are improved compared to those of the smooth, dense films. The ability to tune the ferroelectric properties with the microstructure is primarily relevant for ferroelectric applications such as actuators and systems for energy harvesting and storage

Surface and sub-surface thermal oxidation of ruthenium thin films

For next generation Extreme UV photolithography, multilayer coatings may require protective capping layers against surface contamination. Ruthenium, as a low-oxidation metal, is often used as a reference material. The oxidation behaviour of Ru thin films has been studied using X-ray reflectometry (XRR) and Atomic force microscopy (AFM). XRR is sensitive to the in-depth electron density distribution and as such to the formation of ruthenium oxides. In-situ XRR during atmospheric oxidation reveals formation of a low density RuOX layer near the surface, followed by sub-surface formation of a high density RuOX layer. Surprisingly, the ratio between RuOX formation and Ru consumption is only 1.2, in contrast to the value of 2.3 reported in literature. AFM studies show that the “missing” RuOX is found in surface agglomerates that grow with increasing oxidation temperature and duration. These agglomerates appear around 200˚C, consistent with RuO2 nucleation and growth reported in literature

Structural properties of sub nanometer thick layers to enhance EUV multilayer mirror reflectance

Theoretically a transition metal (TM) interlayer of sub nanometer thickness on top of Mo can improve the dielectric distribution in Mo/Si multilayer structures such, that the EUV reflection at 13.5 nm is increased. To learn the actual effect, the structure and optical properties of B4C/Mo/TM/Si multilayer systems were studied. X-ray reflectometry, AR-XPS and EXAFS at the Mo and transition metal K-edge were used to investigate average interface roughness of the multilayer period and morphology of the transition metal layer and Mo/TM interface. Furthermore EXAFS was used to study the effect of a thin interlayer upon the Mo-silicide formation, suggesting enhanced optical contrast

Influence of DC Bias on the Hysteresis, Loss, and Nonlinearity of Epitaxial PbZr0.55 Ti0.45 O3 Films

The hysteresis, loss, and nonlinearity of the strain and polarization response of an epitaxial PbZr0.55Ti0.45O3 film are experimentally investigated for non-switching AC excitation fields at a DC bias of 20 kV cm−1 in the 70 Hz to 5 kHz range. The measured strain is hysteretic and linear, whereas the polarization is hysteretic and highly nonlinear with excitation amplitude. Furthermore, compared to the case with zero bias, the effective piezoelectric coefficient that is extracted from the strain response is almost not changed for the investigated field range. In contrast, the loss tangent and nonlinearity of the polarization response are strongly reduced. The observations can not be explained by the Rayleigh model and its extensions, but are very well explained by the recently proposed polarization rotation model through addition of a non-zero bias field term to the model. This model describes the film properties as the result of the nonlinear rotation of the polarization vector within the unit-cell in response to the applied field, which is accompanied with viscous domain interaction. These results demonstrate that the polarization rotation model can describe the film response in a broad range of excitation frequencies and amplitudes, which far the applicable range of the Rayleigh  model