G. Abadias

Interdependence between stress, preferred orientation, and surface morphology of nanocrystalline TiN thin films deposited by dual ion beam sputtering

To clarify the underlying mechanisms that cause the preferred orientation in TiN films, we investigated the evolution with the thickness of the texture, surface morphology, and residual stress in TiN thin films deposited by dual ion beam sputtering. The films, with thickness h ranging from 50to300nm, were grown on oxidized Si substrates using a primary Ar ion beam accelerated under 1.2kV and different voltages Va of the (Ar+N2) assistance beam: 25, 50, and 150V. The influence of temperature was also investigated by varying the substrate temperature Ts (25–300°C) during growth or by performing a postdeposition annealing. X-ray diffraction (XRD) as well as transmission electron microscopy were used to study the microstructure and changes of texture with thickness h, while x-ray reflectivity and atomic force microscopy measurements were performed to determine the surface roughness. Residual stresses were measured by XRD and analyzed using a triaxial stress model. The crystallite group method was used for a s...

Diffraction stress analysis in fiber-textured TiN thin films grown by ion-beam sputtering: Application to (001) and mixed (001)+(111) texture

The present study concerns the analysis by x-ray diffraction (XRD) of the residual stresses in fiber-textured TiN thin films grown by sputter deposition. We present an extension of the stress model of Kamminga et al. [J. Appl. Phys. 88, 6332 (2000)] to the case of sputtered thin films having a crystallographic growth texture. The state of stress is triaxial and includes an intrinsic hydrostatic component due to volumetric distortion in the growing layer caused by ion-bombardment-induced point defects, and a biaxial component imposed by the substrate on which the film adheres. Numerical illustration of the model is given for TiN films having a (001) or a mixed (001)+(111) growth texture. It is shown that in the presence of triaxial stresses, the dependence of the lattice parameter with sin2 ψ is still linear, but the stress-free lattice parameter a0 can no longer be determined from the classical strain-free direction. Nevertheless, a direct determination of a0 can be obtained graphically from the intersect...

In situ stress evolution during magnetron sputtering of transition metal nitride thin films

Stress evolution during reactive magnetron sputtering of TiN, ZrN, and TiZrN layers was studied using real-time wafer curvature measurements. The presence of stress gradients is revealed, as the result of two kinetically competing stress generation mechanisms: atomic peening effect, inducing compressive stress, and void formation, leading to a tensile stress regime predominant at higher film thickness. No stress relaxation is detected during growth interrupt in both regimes. A change from compressive to tensile stress is evidenced with increasing film thickness, Ti content, sputtering pressure, and decreasing bias voltage.

Reactive magnetron cosputtering of hard and conductive ternary nitride thin films: Ti–Zr–N and Ti–Ta–N

Ternary transition metal nitride thin films, with thickness up to 300 nm, were deposited by dc reactive magnetron cosputtering in Ar–N2 plasma discharges at 300 °C on Si substrates. Two systems were comparatively studied, Ti–Zr–N and Ti–Ta–N, as representative of isostructural and nonisostructural prototypes, with the aim of characterizing their structural, mechanical, and electrical properties. While phase-separated TiN–ZrN and TiN–TaN are the bulk equilibrium states, Ti1−xZrxN and Ti1−yTayN solid solutions with the Na–Cl (B1-type) structure could be stabilized in a large compositional range (up to x=1 and y=0.75, respectively). Substituting Ti atoms by either Zr or Ta atoms led to significant changes in film texture, microstructure, grain size, and surface morphology, as evidenced by x-ray diffraction, x-ray reflectivity, and scanning electron and atomic force microscopies. The ternary Ti1−yTayN films exhibited superior mechanical properties to Ti1−xZrxN films as well as binary compounds, with hardness ...

Texture and microstructure evolution in single-phase TixTa1−xN alloys of rocksalt structure

The mechanisms controlling the structural and morphological features (texture and microstructure) of ternary transition metal nitride thin films of the TixTa1−xN system, grown by various physical vapor deposition techniques, are reported. Films deposited by pulsed laser deposition, dual cathode magnetron sputtering, and dual ion beam sputtering have been investigated by means of x-ray diffraction in various geometries and scanning electron microscopy. We studied the effects of composition, energetic, and kinetics in the evolution of the microstructure and texture of the films. We obtain films with single and mixed texture as well as films with columnar “zone-T” and globular type morphology. The results have shown that the texture evolution of ternary transition metal nitrides as well as the microstructural features of such films can be well understood in the framework of the kinetic mechanisms proposed for their binary counterparts, thus giving these mechanisms a global application.

Conducting transition metal nitride thin films with tailored cell sizes: The case of δ-TixTa1−xN

We present results on the stability and tailoring of the cell size of conducting δ-TixTa1−xN obtained by film growth and ab initio calculations. Despite the limited solubility of Ta in Ti, we show that TiN and TaN are soluble due to the hybrization of the d and sp electrons of the metal and N, respectively, that stabilizes the ternary system to the rocksalt structure. The stress-free cell sizes follow the Vegard’s rule; nevertheless, process-dependent stresses expand the cell size of the as-grown films. The electronic properties of δ-TixTa1−xN films (ρ=180Ωcm) are similar to those of TiN and TaN.

Nanoscaled composite TiN/Cu multilayer thin films deposited by dual ion beam sputtering: growth and structural characterisation

Abstract We present a detailed structural characterisation of TiN/Cu multilayers, with bilayer period ranging from 5 to 20 nm, deposited by dual ion beam sputtering on Si(001) substrates. Low-angle X-ray diffraction scans exhibit Bragg reflections up to the 15th order, indicative of a well-defined periodicity and non-cumulative roughness. High-angle X-ray diffraction shows that the multilayers adopt a (001) TiN/(001) Cu texture and are polycrystalline in the plane, the mosaic spread for the TiN and Cu grains being of ∼6° and more than 9°, respectively. High Resolution Transmission Electron Microscopy (HRTEM) observations confirm the cube on cube epitaxial growth, but show the presence of several interfacial and growth defects, introduced to relieve the huge misfit (15.9%) between the two lattices. The HRTEM images also reveal facetted islands growth morphology of Cu, leading to lateral roughness at the TiN/Cu interface as well as fluctuations in the interplanar spacings, which could explain the lack of superlattice reflections in the high-angle X-ray diffraction.

Stress field in sputtered thin films: Ion irradiation as a tool to induce relaxation and investigate the origin of growth stress

The stress state of sputtered Mo thin films was studied, and a detailed analysis of elastic strains, using x-ray diffraction and the “sin2 Ψ method,” was performed. The evolution of the lattice parameter under ion irradiation showed that the usual assumption of a biaxial stress state is not adequate to determine the true stress-free lattice parameter a0 of the film. An original stress model, including a hydrostatic component linked to volume distortions induced by point defects, is required. This model, which describes a triaxial stress field, allows a reliable determination of a0. Furthermore, ion irradiation was shown to be a powerful method for stress relaxation, providing a stress-free lattice parameter solely linked to chemical effects.

Atom insertion into grain boundaries and stress generation in physically vapor deposited films

We present evidence for compressive stress generation via atom insertion into grain boundaries in polycrystalline Mo thin films deposited using energetic vapor fluxes (<∼120 eV). Intrinsic stress magnitudes between −3 and +0.2 GPa are obtained with a nearly constant stress-free lattice parameter marginally larger (0.12%) than that of bulk Mo. This, together with a correlation between large compressive film stresses and high film densities, implies that the compressive stress is not caused by defect creation in the grains but by grain boundary densification. Two mechanisms for diffusion of atoms into grain boundaries and grain boundary densification are suggested.

Influence of particle and energy flux on stress and texture development in magnetron sputtered TiN films

The real-time stress evolution during reactive dc magnetron sputter deposition of TiN films in Ar+N2 plasma discharge was measured in situ using a multiple-beam optical stress sensor, while the film texture was determined ex situ using x-ray diffraction. The influence of atomic N/Ti flux and energy flux, previously quantified by combining plasma characterization and Monte Carlo simulations (2009 J. Phys. D: Appl. Phys. 42 053002), was investigated by varying either the N2 partial pressure at fixed total pressure, the total working pressure or the bias voltage applied to the substrate. The contribution of thermal stress was carefully taken into account from thermal probe measurements to evaluate the intrinsic (growth) stress from the measured film force data. A clear correlation between stress, film texture and energy flux is evidenced: while underdense (1?1?1)-textured TiN films with ?V?-shaped columnar growth (zone T) are under tensile stress (up to +0.6?GPa), dense TiN films with zone II microstructure develop a (0?0?2) texture and large compressive stress (up to 3?GPa) when the energy flux is higher than ?150?eV per incoming particle. However, it is shown that a positive or negative bias voltage, though increasing the energy flux, did not promote a (0?0?2) texture. It is concluded that compressive stress development and (0?0?2) preferential growth are both kinetically driven processes in magnetron sputtered TiN layers, but exhibit distinct dependence with the substrate fluxes.