M. Hecq

Influence of pulse duration on the plasma characteristics in high-power pulsed magnetron discharges

High-power pulsed magnetron discharges have drawn an increasing interest as an approach to produce highly ionized metallic vapor. In this paper we propose to study how the plasma composition and the deposition rate are influenced by the pulse duration. The plasma is studied by time-resolved optical emission and absorption spectroscopies and the deposition rate is controlled thanks to a quartz microbalance. The pulse length is varied between 2.5 and 20μs at 2 and 10mTorr in pure argon. The sputtered material is titanium. For a constant discharge power, the deposition rate increases as the pulse length decreases. With 5μs pulse, for an average power of 300W, the deposition rate is ∼70% of the deposition rate obtained in direct current magnetron sputtering at the same power. The increase of deposition rate can be related to the sputtering regime. For long pulses, self-sputtering seems to occur as demonstrated by time-resolved optical emission diagnostic of the discharge. In contrary, the metallic vapor ioniz...

Size and segregation effects on the phase diagrams of nanoparticles of binary systems

The phase diagrams of small particles (with diameters in the nanometre range) are studied theoretically. In the limit where thermodynamical arguments remain valid, it is deduced that the phase diagram of small particles is a function of their size. This is discussed for the cases of eutectics and regular solutions. The effects of surface segregation are also treated and lead to further modifications of the phase diagrams.

Phase diagrams of small particles of binary systems: a theoretical approach

The phase diagrams of small particles (with diameters in the nm range) are studied theoretically. In the limit where thermodynamical arguments remain valid, it is deduced that the phase diagram of small particles is a function of their size. For the case of ideal solutions, it is shown that the lens-shaped solidus-liquidus curves are shifted to lower temperatures when the dimensions of the particle decrease. Additionally, at fixed temperatures between the highest bulk melting point and the lowest melting point of the particle, the relative concentrations of the solid and liquid phases are different in the particle and bulk material.

Functionalization of carbon nanotubes by atomic nitrogen formed in a microwave plasma Ar + N2 and subsequent poly(ε-caprolactone) grafting

Multi-walled carbon nanotubes (MWNTs) are placed under atomic nitrogen flow formed through an Ar + N2 microwave plasma in order to functionalize covalently their side walls with nitrogen-containing groups. The MWNT surface analyzed by X-ray photoelectron spectroscopy shows the presence of amides, oximes and mainly amine and nitrile functions grafted in this way. In order to highlight the actual location of the amine functions grafted on MWNTs, they were considered as initiation species in ring-opening polymerization of e-caprolactone using triethylaluminium as activator. The so-generated poly(e-caprolactone) chains remain grafted on the MWNTs via amide bonds and form polyester islets along the nanotubes surface. TEM images of these MWNT surfaces grafted with poly(e-caprolactone) show a good amino-sidewall distribution. This work demonstrates the side-wall amino-functionalization of carbon nanotubes readily achieved by microwave plasma with the possibility to reach within a short time period very high contents in nitrogen-based functions (∼10 at.%).

Study of ZrN layers deposited by reactive magnetron sputtering

Zirconium nitride films are deposited onto borosilicate wafers by reactive magnetron sputtering. The films are analysed in situ by X-ray photoelectron spectroscopy (XPS). We have studied by XPS the effects of the nitrogen partial pressure (1–100%), the subtract temperature (ambient to 450 °C), and biasing (0–80 W) on the stoichiometry of ZrN films. The N1s peak is composed of three components at 397.2, 396.4 and 395.8 eV in binding energy. These components are correlated with the three existing phases of zirconium nitride (ZrN, Zr3N4 and ZrN2). With an increase of the nitrogen partial pressure, a shift of the Zr3d line to the high binding energy and the increase of the N1s component at 395.8 eV are observed. These observations are explained by the charge transfer between Zr to N which increases with P(N2) as previously described for the Ti–N2 system [1]. The bulk stoichiometry is calculated by Rutherford backscattering and nuclear reaction measurements. The resistivity of the films is measured by the four-point probes technique. The reflectivity of the films are recorded by a spectrophotometer in the IR–Vis range. A correlation between the reflectivity and the resistivity is observed. The roughness of the films is measured by atomic force microscopy. The bias voltage has a great influence on the surface roughness and on the reflectivity of the films. The dependence of the ZrNx films structure and morphology with the discharge parameters is established.

XPS study of TiOx thin films prepared by d.c. magnetron sputtering in Ar–O2 gas mixtures

Titanium oxide films have been deposited, at a pressure of 5 mTorr and a discharge current of 500 mA, on borosilicate glass substrates. We have studied in situ by XPS the dependence of film composition on oxygen partial pressure. All the experiments have been performed under high vacuum; there is no air contamination of film surfaces before XPS analysis. The ions produced in the plasma have been analysed by glow discharge mass spectrometry (GDMS). The stoichiometry of the films is compared to the plasma composition. The XPS results show that for an increasing oxygen partial pressure four regimes are observed. At very low oxygen concentration ( 15% (zone IV) a pure TiO 2 film is obtained. When zone IV starts, the Ti + mass spectrometric signal is still higher than the TiO + signal, showing that a pure TiO 2 phase is occurring at the substrate while the sputtering mode is still partially metallic.

Growth of ultrathin Ti films deposited on SnO2 by magnetron sputtering

Abstract Low-e multilayers, such as dielectric/Ag/dielectric/glass, are systems extensively used in the field of architectural glass for thermal insulation. However, the physical and chemical phenomena that occur at interfaces are still not fully understood, in particular the function of the sacrificial layer deposited between the dielectric and the silver layers. Most of the time, the sacrificial layer is made of a very thin film of titanium. In order to understand the growth modes of Ti film on SnO2 substrate, as well as the chemical mechanisms taking place at the interface, we have studied by X-ray photoelectron spectroscopy (XPS) the growth of successive amounts of titanium (additions of 0.5 nm) deposited by DC magnetron sputtering on SnO2 substrate. The Ti deposition rate was varied between 0.05 and 0.02 nm/s by varying the current target between 100 and 40 mA in order to determine its influence on the growth mechanism of Ti films. The Ti deposition on SnO2 layers induces the reduction of Sn and partial oxidation of Ti. The Ti films deposited at high deposition rate reach a surface metallic state more rapidly. The XPS results and the fitting of the Sn attenuation signal by a Ti overlayer show that the Ti deposition rate influences the titanium growth mode. We found that the growth mode changes from a Volmer Weber mode for low deposition rate (0.02 nm/s) to a pseudo Frank van der Merwe mode when the deposition rate is enhanced (0.05 nm/s).

Measurement of ionic and neutral densities in amplified magnetron discharges by pulsed absorption spectroscopy

Resonant absorption diagnostic has been used to estimate densities of neutral and ionic titanium, both in ground and metastable states, in a rf coil amplified magnetron sputtering process. The conventional optical source dc supply has been replaced by a high voltage pulsed power supply to allow absorption experiments onto ionic and neutral species, in a broad range of discharge conditions (500 W are applied onto the magnetron cathode and 0–500 W on the rf coil, for a 30 mTorr argon pressure). The obtained densities are used to compare the magnetron and the amplified discharges. The total ionization degree of the metallic vapor is found to increase from ∼3% in the magnetron regime to ∼24% in the amplified magnetron discharge. The Ti (a5F) neutral metastable density is found to be partially enhanced when the rf coil is power supplied.

Analysis of DC magnetron discharges in Ar- gas mixtures. Comparison of a collisional-radiative model with optical emission spectroscopy

DC magnetron discharges in argon-nitrogen gas mixtures have been characterized by optical emission spectroscopy (OES). Optical lines from the cathode species (aluminium) and the gas mixture (argon, nitrogen) have been measured at constant total pressure, as a function of the gas mixture composition and electrical power. The experimental data are compared with results of a theoretical plasma model which solves self-consistently the Boltzmann equation for electrons and the kinetic equations for aluminium, argon, molecular and atomic nitrogen states. The emission intensity variations of plasma species have been analysed versus the nitrogen relative concentration and electrical power and compared with calculated populations of emitting species with a satisfactory agreement. The variation of aluminium density versus the nitrogen concentration has been deduced by using the line intensity and excitation rates given by the model.

Transport of ionized metal atoms in high-power pulsed magnetron discharges assisted by inductively coupled plasma

Transporting metallic ions from the magnetron cathode to the substrate is essential for an efficient thin-film deposition process. This letter examines how inductively coupled plasma superimposed onto a high-power pulsed magnetron discharge can influence the mobility of titanium ions. To this effect, time-resolved optical emission and absorption spectrometry are conducted and the current at the substrate is measured. With this new hybrid technique, ions are found to reach the substrate in two successive waves. Metal ions, only present in the second wave, are found to accelerate proportionally to the power supplied to the inductively coupled plasma. All the measurements in this study are made at 10 and 30mTorr, with 10μs long pulses at the magnetron cathode.