Kostas Sarakinos

On the deposition rate in a high power pulsed magnetron sputtering discharge

The effect of the high pulse current and the duty cycle on the deposition rate in high power pulsed magnetron sputtering (HPPMS) is investigated. Using a Cr target and the same average target curre ...

On the relationship between the peak target current and the morphology of chromium nitride thin films deposited by reactive high power pulsed magnetron sputtering

High power pulsed magnetron sputtering (HPPMS) is used to deposit CrN films without external heating at different peak target currents, while the average current is kept constant. Films are also grown by dc magnetron sputtering (dcMS), for reference. The plasma properties, the deposition rate and the morphology of the films are investigated. The plasma analysis reveals that HPPMS provides higher fluxes of ionized species (both gas and sputtered) to the growing film, as compared with dcMS. In addition, the ionic bombardment during HPPMS increases, when the peak target current is increased. The HPPMS films exhibit changes of the density and the surface roughness as the peak target current increased, while the deposition rate decreases drastically. Furthermore, it is found that different thin-film morphologies are obtained starting from a porous columnar morphology for the dcMS films, which turns to a dense columnar one at low peak target currents and ends up to a featureless morphology at high peak target currents for the films grown by HPPMS. A new structure zone model specific for high ionization sputtering is, therefore, outlined.

On the phase formation of titanium oxide films grown by reactive high power pulsed magnetron sputtering

High power pulsed magnetron sputtering is used for the growth of titanium dioxide (TiO2) films at different working pressures and orientations of the substrate with respect to the target surface. In the case of substrates oriented parallel to the target surface, the increase in the working pressure from 0.5 to 3 Pa results in the growth of crystalline TiO2 films with phase compositions ranging from rutile to anatase/rutile mixtures. When depositions are performed on substrates placed perpendicularly to the target surface, rutile films that consist of TiO2 nanocrystals embedded in an amorphous matrix are obtained at 0.5 Pa. Increase in the working pressure leads to the deposition of amorphous films. These findings are discussed in the light of the energetic bombardment provided to the growing film at the various deposition conditions.

Ab initio molecular dynamics of Al irradiation-induced processes during Al2O3 growth

Al bombardment induced structural changes in alpha-Al(2)O(3) (R-3c) and gamma-Al(2)O(3) (Fd-3m) were studied using ab initio molecular dynamics. Diffusion and irradiation damage occur for both polymorphs in the kinetic energy range from 3.5 to 40 eV. However, for gamma-Al(2)O(3)(001) subplantation of impinging Al causes significantly larger irradiation damage and hence larger mobility as compared to alpha-Al(2)O(3). Consequently, fast diffusion along gamma-Al(2)O(3)(001) gives rise to preferential alpha-Al(2)O(3)(0001) growth, which is consistent with published structure evolution experiments.

On the phase formation of sputtered hafnium oxide and oxynitride films

Hafnium oxynitride films are deposited from a Hf target employing direct current magnetron sputtering in an Ar-O(2)-N(2) atmosphere. It is shown that the presence of N(2) allows for the stabilizati ...

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.

Low temperature synthesis of α-Al2O3 films by high-power plasma-assisted chemical vapour deposition

In this study, we deposit Al2O3 films using plasma-assisted chemical vapour deposition (PACVD) in an Ar–H2–O2–AlCl3 atmosphere. A novel generator delivering approximately 4 times larger power densities than those conventionally employed in PACVD enabling efficient AlCl3 dissociation in the gas phase as well as a more intense energetic bombardment of the growing film is utilized. We demonstrate that these deposition conditions allow for the growth of dense α-Al2O3 films with negligible Cl incorporation and elastic properties similar to those of the bulk α-Al2O3 at a temperature of 560 ± 10 °C.

Influence of ionization degree on film properties when using high power impulse magnetron sputtering

Chromium thin films are deposited by combining direct current magnetron sputtering and high power impulse magnetron sputtering (HiPIMS) on a single cathode in an industrial deposition system. While maintaining a constant deposition rate and unchanged metal ion energy distribution function, the fraction of the total power supplied by either deposition technique is altered, and thereby also the metal ion to metal neutral ratio of the deposition flux. It is observed that the required total average power needed to be proportionally increased as the HiPIMS fraction is increased to be able to keep a constant deposition rate. The influence on microstructure, electrical, and electrochemical properties of the films is investigated and shows improvements with the use of HiPIMS. However, considerable influence of the studied properties occurs already when only some 40% of the total power is supplied by the HiPIMS technique. Further increase of the HiPIMS power fraction results in comparatively minor influence of the studied properties yet significant deposition rate efficiency reduction. The results show that the degree of ionization can be controlled separately, and that the advantages associated with using HiPIMS can be obtained while much of the deposition rate reduction, often reported for HiPIMS, can be avoided.

Ab initio study of effects of substitutional additives on the phase stability of γ-alumina

Using ab initio calculations, we have evaluated two structural descriptions of γ-Al(2)O(3), spinel and tetragonal hausmannite, and explored the relative stability of γ-Al(2)O(3) with respect to α-Al(2)O(3) with 2.5 at.% of Si, Cr, Ti, Sc, and Y additives to identify alloying element induced electronic structure changes that impede the γ to α transition. The total energy calculations indicate that Si stabilizes γ-Al(2)O(3), while Cr stabilizes α-Al(2)O(3). As Si is added, a bond length increase in α-Al(2)O(3) is observed, while strong and short Si-O bonds are formed in γ-Al(2)O(3), consequently stabilizing this phase. On the other hand, Cr additions induce a smaller bond length increase in α-Al(2)O(3) than in γ-Al(2)O(3), therefore stabilizing the α-phase. The bulk moduli of γ-Al(2)O(3) with these additives show no significant changes. The phase stability and elastic property data discussed here underline the application potential of Si alloyed γ-Al(2)O(3) for applications at elevated temperatures. Furthermore it is evident that the tetragonal hausmannite structure is a suitable description for γ-Al(2)O(3).

A semi-quantitative model for the deposition rate in non-reactive high power pulsed magnetron sputtering

A theoretical treatment of the deposition process in a non-reactive high power pulsed magnetron sputtering discharge is presented. This leads to the development of a semi-quantitative model that describes the deposition rate as a function of process parameters, such as the target voltage, the peak target current density, the pulse frequency and the pulse duty cycle. The effect of these parameters on the deposition rate is studied experimentally using carbon, chromium and copper targets. The implementation of the model on the experimental results enables the estimation of the relative fractions of the sputtering gas ions (Ar+) and the sputtered metal ions (M+) in the total ion flux at the target. The M+ content in the target ion current is calculated to adopt values up to ~72% and ~98% for the chromium and the copper targets, respectively. In contrast, the target ion current is found to consist mostly of Ar+ species in the case of the carbon target. The significantly higher fractions of M+ ions for chromium and copper are attributed to their higher ionization probability and their higher sputtering yield in comparison with carbon.