Reaction paths and kinetics of aluminide formation in Al/epitaxial-W(001) model diffusion barrier systems
- Coordinated Science Laboratory, Materials Research Laboratory, and Department of Materials Science, 1101 West Springfield, University of Illinois, Urbana, Illinois 61801 (United States)
Single-crystal bcc W(001) layers, 140 nm thick, were grown on MgO(001) substrates by ultrahigh-vacuum (UHV) magnetron sputter deposition at {ital T}{sub {ital s}}=600 {degree}C. Al overlayers, 190 nm thick with strong (001) and (011) preferred orientation and an average grain size of 200 nm, were then deposited at {ital T}{sub {ital s}}=100 {degree}C without breaking vacuum. Changes in bilayer sheet resistance {ital R}{sub {ital s}} were monitored continuously as a function of time {ital t}{sub {ital a}} and temperature {ital T}{sub {ital a}} during UHV annealing. In addition, Rutherford backscattering spectroscopy, x-ray diffraction, transmission electron microscopy (TEM), and scanning TEM, in which cross-sectional specimens were analyzed by energy-dispersive x-ray analysis with a 1 nm resolution, were used to follow area-averaged and local interfacial reaction paths as well as microstructural changes as a function of annealing conditions. The initial reaction products were discontinuous regions of monoclinic-structure WAl{sub 4} which exhibit a crystallographic relationship with the underlying W layer. bcc WAl{sub 12} forms at a later stage and grows conformally to cover both W and WAl{sub 4}. WAl{sub 4} and WAl{sub 12} continue to grow, with W being the primary mobile species, until the Al layer is completely consumed. Information from the microchemical and microstructural analyses was used to model the {ital R}{sub {ital s}}({ital T}{sub {ital a}},{ital t}{sub {ital a}}) results based upon a multielement equivalent circuit approach which accounts for the observed nonplanar nature of the reaction front. Reaction kinetics and activation energies were determined. The results show that the growth of WAl{sub 4} is diffusion limited with an activation energy {ital E}{sub {ital a}} of 3.1 eV while the formation of WAl{sub 12} is reaction limited with {ital E}{sub {ital a}}=3.3 eV. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
- OSTI ID:
- 64892
- Journal Information:
- Journal of Applied Physics, Vol. 78, Issue 1; Other Information: PBD: 1 Jul 1995
- Country of Publication:
- United States
- Language:
- English
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