Thermal He desorption spectrometry was used for the investigation of defects and thermal stability of thin Cu films (5 to 200Å) deposited on a polycrystalline Mo substrate in ultra-high vacuum. These films were metastable at room temperature. On heating, the films transform into islands, giving rise to a relatively broad peak in the He desorption spectra. The temperature of this island formation was dependent on film thickness, being 417K for 10Å and 1100K for a 200Å film. The activation energy for island formation was found to be 0.3eV for 75Å film. Grain boundaries have a strong effect on island formation. The defect concentration in the as-deposited films was ~5 x 10–4, for films thicker than 50Å and more for thinner films. Helium release from monovacancies was identified in the case of a 200Å film. Helium release was also seen during sublimation of the Cu film (~1350K). Overlayer experiments were used to identify He trapped close to the film surface. An increase of the substrate temperature during deposition resulted in a film that had already formed islands. Argon-ion assistance (250eV) during film deposition with an ion/atom ratio of ~0.1 resulted in a significant enhancement of He trapping in the films. The Ar concentration in the films was found to be 10–3. The temperature of island formation was increased due to Ar-ion assistance. The He and Ar desorption spectra were found to be similar, which was due to most of the He becoming trapped in the defects created by the Ar beam. The role of the Mo surface in affecting the defects at the film-substrate interface was investigated. The effect of variation of He fluence and He implantation energy was also considered. The present THDS results of Cu/poly-Mo were compared to those of Cu/Mo(100) and Cu/Mo(100) reported earlier.

Defects and Morphological Changes in Nanothin Cu Films on Polycrystalline Mo Analyzed by Thermal Helium Desorption Spectrometry. V.Venugopal, L.J.Seijbel, B.J.Thijsse: Journal of Applied Physics, 2005, 98[2], 024315 (12pp)