INFLUENCE OF ION-BOMBARDMENT DURING DEPOSITION ON MICROSTRUCTURE OF EVAPORATED ALUMINUM FILMS

Aluminum films of approximately 5-mu-m thickness were deposited on oxidized Si wafers at T almost-equal-to 260-degrees-C by UHV evaporation under simultaneous Kr or Xe bombardment. Normalized energies, E(n), ranged from 0 to 200 eV/at. Microstructural characterization using X-ray diffraction, transmission electron microscopy, small-angle X-ray scattering and thermal desorption spectroscopy gave the following results: (1) Ion bombardment leads to a reduction of the grain size, especially near the film substrate interface by more than an order of magnitude. (2) For E(n) greater-than-or-equal-to 80 eV/at. a {111} "single-crystal" texture develops with the crystals aligned to the ion beam direction. (3) For E(n) greater-than-or-equal-to 30 eV/at. the gas content saturates at about 1 and 3 at.% for Xe and Kr, respectively. (4) The enclosed rare gas precipitates in a solid phase in small bubbles of approximately 2 nm diameter. The resulting Xe and Kr crystals have fcc structure and are epitaxially aligned with the surrounding Al lattice. (5) In addition to the small bubbles there are but fewer large voids of a typical diameter of approximately 10 nm. The evolution of film stress and grain size with E(n) will be discussed in terms of gas incorporation and precipitation.