Thermal He desorption spectrometry was used for a comprehensive experimental investigation of vacancy-related defects and thermal stability of nanothin Cu films (10–300Å) deposited on a Mo(100) substrate at 300K in ultra-high vacuum. In the He desorption spectra (300–2000K), a peak was observed that showed that the Cu films were highly unstable. Post-deposition annealing treatments show that this peak was due to the thermally-induced island formation of the Cu films. This process was strongly dependent on film thickness; its temperature ranging from 429K for a 10Å film to 1312K for a 300Å film, which was not simply due to the considerable change of stress with film thickness. Between 70 and 75Å, there was a distinct narrowing of the peak shape, indicating a change in the kinetics. For a 100Å film lying in the large thickness range, an activation energy E = 1.2eV was determined. The island-formation process was defect-mediated, as suggested by the fact that the temperature was lowered by an increase of the He implantation energy and fluence. The island formation during deposition at an elevated substrate temperature occurred at a lower temperature than during post-deposition annealing. The He released from monovacancies (E = 1.8eV) and vacancy clusters in the Cu films and during high-temperature evaporation of the Cu films from the Mo substrate (Esubl = 3.5eV) was also identified. The X-ray diffraction measurements on 60 and 200Å films show that they were both face-centered cubic Cu(100) films with identical macrostrains; the 200Å film has a sharper texture than the 60Å film. The orientation relation between the film and the substrate was found to be (100)[100]Cu||(100)[110]Mo.

Defects and Morphological Changes in Nanothin Cu Films on Mo(100) Studied by Thermal Helium Desorption Spectrometry. V.Venugopal, L.J.Seijbel, N.M.van der Pers, B.J.Thijsse: Journal of Applied Physics, 2004, 96[8], 4463-74