Aluminide formation in polycrystalline Al/W metal/barrier thin-film bilayers: Reaction paths and kinetics
- Coordinated Science Laboratory, Materials Research Laboratory, and Department of Materials Science, 1101 West Springfield, University of Illinois, Urbana, Illinois 61801 (United States)
Polycrystalline bcc W layers, 110 nm thick with 011 preferred orientation and an average grain size of 40 nm, were grown on amorphous-SiO{sub 2}/Si(001) substrates by ultrahigh vacuum (UHV) magnetron sputter deposition at T{sub s}=600{degree}C. Al overlayers, 170 nm thick with strong 111 preferred orientation and an average grain size of 120 nm, were then deposited at T{sub s}=100{degree}C without breaking vacuum. Changes in bilayer sheet resistance R{sub s} were monitored continuously as a function of time t{sub a} and temperature T{sub a} during UHV annealing. In addition, area-averaged and local interfacial reaction paths, as well as microstructural changes as a function of annealing conditions, were determined by x-ray diffraction, Rutherford backscattering spectroscopy, transmission electron microscopy (TEM), and scanning TEM in which compositional distributions in cross-sectional specimens were obtained by energy-dispersive x-ray analysis using a 1 nm diam probe beam. The two tungsten aluminides which form, WAl{sub 4} and WAl{sub 12}, are nucleated essentially immediately with no measurable induction time. WAl{sub 4} grains, extensively twinned, increase in size during the initial reaction, then stop growing as competitive growth in the diffusion limited regime favors WAl{sub 12}. Information from microstructural and microchemical analyses was used to model the R{sub s}(T{sub a},t{sub a}) data in order to determine reaction kinetics and activation energies. The results show that WAl{sub 12} growth is limited by W diffusion, with an activation energy of 2.7 eV, to the Al/aluminide interface. {copyright} {ital 1997 American Institute of Physics.}
- Research Organization:
- Univ. of Illinois at Urbana-Champaign, IL (United States)
- DOE Contract Number:
- AC02-76ER01198
- OSTI ID:
- 530037
- Journal Information:
- Journal of Applied Physics, Vol. 82, Issue 1; Other Information: PBD: Jul 1997
- Country of Publication:
- United States
- Language:
- English
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