C. Rousselot

Microstructure modification of amorphous titanium oxide thin films during annealing treatment

Abstract Thin films of titanium oxide have been deposited on (100) silicon wafers and on quartz substrates by reactive r.f. magnetron sputtering from a 99.6% pure Titanium target. Amorphous and overoxidised coatings (TiO2.2) have been obtained from this technique. The influence of the post-deposition annealing between 300 °C and 1100 °C on the structural and optical properties and on the surface morphology has been investigated. The results of X-ray diffraction showed that films annealed from 300 to 500 °C have an anatase crystalline structure whereas those annealed at 1100 °C have a rutile crystalline structure. Optical analyses showed that UV-Vis transmission spectra are strongly modified by the annealing temperature and refractive index of TiOx layers also changes. Atomic force microscopy measurements corroborate optical and structural analyses and showed that the surface of the coatings can have various appearances and morphologies for the annealing temperatures investigated.

The effect of bias power on some properties of titanium and titanium oxide films prepared by r.f. magnetron sputtering

Titanium and titanium oxide thin films have been deposited on (100) silicon wafers and glass substrates by r.f. reactive sputtering magnetron. Substrates have been r.f. biased during the growth of the film and the influence of the bias power on some properties of the coatings has been investigated. The results of the deposition rate measurements show that this is weakly affected when bias power is low. As the r.f. bias power increases, the deposition rate decreases strongly due to an increase of the layer density and resputtering phenomena. Atomic force microscopy showed that the surface morphology of metallic and oxide films can be modified using bias treatment. Roughness analyses exhibited a similar evolution as the deposition rate and surface topography when bias power changes. Optical properties like refractive index followed the same variations as previous results. So, when r.f. bias power increases, various phenomena take place and different zones can be defined from these investigations. Argon ion to atom arrival rate ratio and average energy per deposited atom have been calculated from experimental values of current density applied to the substrate and energy of argon ions impinging on the growing film. Their evaluations have been discussed for metallic and oxide materials.

Use of a theoretical model to investigate RF and DC reactive sputtering of titanium and chromium oxide coatings

Abstract An analysis of RF and DC reactive sputtering techniques is presented. The transition between a metal sputtering mode and a compound sputtering mode is usually noticed with a metallic target and an argon+oxygen gas mixture. The so-called hysteresis effect often observed for small amounts of reactive gas is explained in recent models. By considering gas kinetics parameters, it is possible to evaluate quite simple relationships between the main processing parameters. These theoretical calculations enable the prediction and aid the understanding of instability phenomena observed in reactive sputtering. In this paper, the effects of some parameters on the position and size of instability regions are discussed, and the difference between DC and RF reactive deposition is investigated. Simulations and experimental results are compared for the case of titanium and chromium oxide thin films prepared by DC and RF reactive sputtering. The influence of sputtering power on the position of the hysteresis loop is analysed theoretically and experimentally, and the changes observed between the reactive sputtering of titanium and chromium oxide materials are also discussed.

Instabilities of the reactive sputtering process involving one metallic target and two reactive gases

The present article considers instability phenomena during the sputtering of a single metallic target of titanium in a reactive atmosphere involving argon+oxygen+nitrogen gases. Since the process using two reactive gases is much more complex than one reactive gas, the transition zone of the reactive mode must be defined taking into account oxygen and nitrogen mass flow rates. A two-dimensional representation delimiting boundaries of the instability region and depending on both mass flows is proposed for radio frequency and direct current (dc) polarization of the titanium target. This diagram provides operating conditions favorable to deposit oxy-nitride coatings with a modulated oxygen or nitrogen composition. It is also shown that the supply of one reactive gas affects consumption and behaviors of the other gas as well as its own characteristics. A critical region is then defined in which the process is trapped in reactive mode and can not go back to elemental conditions by changing the mass flow rate of...

Influence of two reactive gases on the instabilities of the reactive sputtering process

Since the process using two reactive gases is much more complex than one reactive gas, the transition zone of the reactive mode must be defined taking into account oxygen and nitrogen mass flow rates. A two-dimensional representation delimiting boundaries of the instability region and depending on both mass flows is proposed for RF and DC polarisation of the titanium target. This diagram allows to determine operating conditions favourable to deposit oxynitride coatings with a modulated oxygen or nitrogen composition. It is also shown that the supply of one reactive gas affects consumption and behaviours of the other gas as well as its own characteristics. A critical region is then defined in which the process is trapped in reactive mode and cannot go back to elemental conditions by changing mass flow rate of only one reactive gas. Kinetics and pollution of the titanium surface is discussed from measurements of DC potential for various operating points. It is shown that comportments of oxygen and nitrogen towards metallic or poisoned target are interdependent and a surprising evolution of the time of pollution against oxygen and nitrogen introduction is observed.

Structural, optical and electrical properties of reactively sputtered iron oxynitride films

In this paper, the properties of iron oxynitride films prepared by magnetron sputtering of an iron target in Ar–N2–O2 reactive mixtures using constant nitrogen and argon flow rates are presented. The oxygen flow rate varied from 0 to 2 sccm. The thickness of the films deposited on silicon substrates ranged from 0.2 to 2 µm. The structure and chemical composition of these films were determined by x-ray diffraction and Rutherford backscattering spectrometry, respectively. These studies revealed the formation of a new fcc intermediate phase of iron oxynitride FeNxOy films between iron nitride (e-Fe2N) and an oxide close to Fe2O3. In addition, optical and electrical properties measurements at room temperature were investigated during this work. Refractive index and extinction coefficient were determined from spectroscopic ellipsometry. The electrical behaviour of the films evolved from a metallic one to a semiconductor one which is consistent with other investigations. In order to determine the morphology of the films, scanning electron microscopy was used.

Electronic and atomic structures of Ti1−xAlxN thin films related to their damage behavior

Ti and AlK-edge x-ray absorption spectroscopy is used to investigate the electronic structure of Ti1−xAlxN thin films deposited by reactive magnetron sputtering. The experimental near edge spectra of TiN and AlN are interpreted in the light of unoccupied density of state band structure calculations. The comparison of the structural parameters derived from x-ray absorption fine structure and x-ray diffraction reveals segregation between Al-rich and Ti-rich domains within the Ti1−xAlxN films. Whereas x-ray diffraction probes only the crystallized domains, the structural information derived from extended x-ray absorption fine structure analysis turns on both crystalline and grain boundaries. The results are discussed by considering the damage behavior of the films depending on the composition.

Electrochromic thin films deposited onto polyester substrates

The results of in situ measurements of the electrochemical and optical properties of tungsten trioxide (WO3) thin films obtained by vacuum evaporation onto transparent and conductive plastic substrates are presented. Much attention is focused on the procedure used to obtain the electrochromic films. These electrochromic layers have been tested in lithium electrolyte. Moreover, the electrochemical behaviour of two transparent electrodes deposited onto polyester, and previously used as the eletrochromic electrode substrates, has been investigated in lithium electrolyte in order to use them as a counterelectrode in a transmissive electrochrome device.

Structural properties of iron oxynitride films obtained by reactive magnetron sputtering

Iron oxynitride films were prepared by magnetron sputtering of an iron target in Ar?N2?O2 reactive mixtures using a nitrogen flow rate of 2?sccm and a constant argon pressure of 0.3?Pa. The oxygen flow rate varied from 0 to 2?sccm. The thickness of the films deposited on silicon (100) and glass substrates ranged from 0.5 to 2??m. In order to determine the chemical composition of the films, Rutherford backscattering spectrometry was used. Whatever the iron, nitrogen and oxygen contents, this study revealed that the film composition was homogeneous along the film depth. The films were characterized by several complementary experimental techniques, such as x-ray diffraction, x-ray photo-electron spectroscopy and 57Fe M?ssbauer spectrometry, which gave the most accurate information about the short-range order of iron atoms. Due to their different spatial scale efficiency, the analysis by both 57Fe transmission and conversion electron M?ssbauer spectrometry and x-ray diffraction allowed us to characterize both the structural and microstructural nature of these films. The study of the films by x-ray diffraction indicated an evolution of the structure from iron nitride ?-Fe2N or ?-Fe2N to an fcc intermediate phase and finally to an oxide-like Fe2(O,N)3. The hyperfine structure observed on the M?ssbauer spectra for the intermediate phase showed the presence of a phase of iron oxynitride Fe1.06O0.35N0.65 which is consistent with the x-ray diffraction results.

Structural and Mechanical Characterizations of Ni-Mn-Ga Thin Films Deposited by R.F. Sputtering and Heat-Treated

The near-stoichiometric Ni2MnGa ferromagnetic alloys are one of these smart materials, that show a great interest when they are deposited as a thin film by rf sputtering. These thin films of shape memory alloys (SMAs) are prospective materials for micro and nanosystem applications. However, the properties of the SMAs polycrystalline thin films depend strongly on their structure and internal stress, which develop during the sputtering process and also during the post-deposition annealing treatment. In this study, 1μm Ni55Mn23Ga22 thin films were deposited at 0.45 and 1 Pa of Ar and their composition, crystallographic structure, internal stress, indentation modulus, hardness and deflection induced by magnetic field were systematically studied as a function of the temperature of the silicon substrate ranging from 298 to 873 K and the vacuum annealing treatment at 873 K for 21 and 36 ks. A silicon wafer having a native amorphous thin SiOx buffer layer was used as a substrate. This substrate influences the microstructure and blocks the diffusion process during the heat treatment. The crystal structure of the martensitic phase in each film was changed systematically from bct or 10M or 14M. In addition, the evolution of the mechanical properties such as means stress, roughness, hardness and indentation modulus with the temperature (of substrate or of heat treatment) were measured and correlated to crystal structure and morphology changes. It is concluded that the response of a free-standing magnetic SMAs films to a magnetic field of 200 kA/m depends strongly on the martensitic structure, internal mechanical stress (mean and gradient) and magnetic properties. The free-standing annealed film at 873 K for 36 ks demonstrates a considerable magnetic actuation associated with bct or 10M or 14M martensitic structures.