Effect of Ion Energy on Structure and Composition of Cathodic Arc Deposited Alumina Thin Films

Abstract

The effect of energy supplied to the growing alumina film on the composition and structure has been investigated by varying substrate temperature and substrate bias potential. The constitution and composition were studied by X-ray diffraction and elastic recoil detection analysis, respectively. Increasing the substrate bias potential from −50 to −100 V caused the amorphous or weakly crystalline films to evolve into stoichiometric, crystalline films with a mixture of the α-and γ -phase above 700 o C, and γ -phase dominated films at temperatures as low as 200 o C. All films had a grain size of <10 nm. The combined constitution and grain size data is consistent with previous work stating that γ -alumina is thermodynamically stable at grain sizes <12 nm [McHale et al., Science 277, 788 (1997)]. In order to correlate phase formation with synthesis conditions, the plasma chemistry and ion energy distributions were measured at synthesis conditions. These results indicate that for a substrate bias potential of −50 V, ion energies in excess of 100 eV are attained, both from a high energy tail and the accelerated ions with charge >1. These results are of importance for an increased understanding of the evolution of film composition and microstructure, also providing a pathway to γ -alumina growth at temperatures as low as 200 o C.

Energy distributions of positive and negative ions during magnetron sputtering of an Al target in Ar∕O2 mixtures

“…We interpret the higher energy species as originating from the cathode. Bombardment by these species will increase the mobility at the growth surface, but, according to previous works, 10,28,29 should not be energetic enough to induce the observed phase changes. In contrast, the measurements show that the more energetic negative oxygen ions are a likely explanation for the observed film results.…”

“…10,28,29 Importantly, in relation to the present work, the ␣ phase was promoted in those studies by high energies ͑Ͼ100 eV͒ of the depositing species, achieved by the applied substrate bias. In our case 6 no bias was applied and, as judged from the dc measurements presented in Fig.…”

Synthesis of α-Al 2 O 3 thin films using reactive high-power impulse magnetron sputtering

“…The film deposited at 575 °C contains γ-alumina, as most easily identified by the peak at 2θ ≈ 67°, while the films deposited at 500 and 400 °C are essentially xray amorphous. Note, however, that γ-alumina, due to the inherent properties of this phase [28], often forms a very small-grained structure and that the existence of nanocrystalline γ-alumina in the two latter samples therefore cannot be excluded without further investigations using, e.g., transmission electron microscopy.…”

“…Possible suggestions include removal of impurities [26,27] promotion of diffusion processes [28], and stress and defect generation [28]. …”

Influence of Gas Entry Point on Plasma Chemistry, Ion Energy and Deposited Alumina Thin Films in Filtered Cathodic Arc

“…Aluminum plasma generated using cathodic arc, for example, contains ion charge states of up to three, and the ion energy distributions (IEDs) extend up to 250 eV [11]. It is known that the introduction of background gas influences the plasma properties through a changed plasma chemistry [12], and reduced ion charge states [13,14] and ion energies [15][16][17][18][19][20] Studies including detailed plasma characterisation with subsequent thin film growth are comparatively rare [21,22], though more common are investigations showing that film structure and film properties are very dependent on process parameters used. Studies have been made on for example the effect of arc method [23], plasma filtering method [24], pressure [25], and substrate bias potential (i.e.…”