Characterization of aluminium films deposited by ion-beam-assisted ultrahigh vacuum evaporation

Abstract

Ion bombardment during deposition enables the microstructure and properties of thin films to be manipulated in a controlled manner. Aluminium films approximately 5 μm thick were deposited on oxidized silicon wafers at T≈250 °C by ultrahigh vacuum electron beam evaporation. For normalized energies E n in the range 0–200 eV (Al atom) -1 the influence of krypton and xenon ion bombardment during evaporation was investigated by X-ray diffraction, transmission electron microscopy, small angle X-ray scattering, scanning electron microscopy and thermal desorption spectroscopy. The results are discussed in terms of the change in texture, stress, grain size and content of gas bubbles. For 5 eV < E n<40 eV a characteristic tilt of the 〈111〉 fibre axis by approximately 20° away from the surface normal is observed. This tilt is attributed to an ion-assisted interface reaction during the beginning of the deposition process. For E n≈100–200 eV, a (111) “single crystal” texture develops with the crystal aligned to the ion beam direction. For E n>40 eV the average rare gas content saturates at about 1 at.% and 3 at.% for xenon and krypton respectively. The gas precipitates within smaller bubbles as high-density f.c.c. solid epitaxially oriented with the aluminium. The distribution of bubbles is rather inhomogeneous even within individual grains.