Al/Ti{sub x}W{sub 1{minus}x} metal/diffusion-barrier bilayers: Interfacial reaction pathways and kinetics during annealing
- Coordinated Science Laboratory, Materials Research Laboratory, and Department of Materials Science, University of Illinois, Urbana, Illinois 61801 (United States)
Polycrystalline bcc Ti{sub x}W{sub 1{minus}x} layers with mixed 011 and 002 texture were grown on oxidized Si(001) substrates at 600{degree}C by ultrahigh-vacuum (UHV) sputter deposition from W and Ti{sub 0.33}W{sub 0.67} targets using both pure Ar and Xe discharges. Ti concentrations in the 100-nm-thick layers were 0, 6, and 33 at.{percent} depending on target composition and sputtering gas. Al overlayers, 190 nm, thick with strong 111 preferred orientation, were then deposited in Ar at 100{degree}C. Changes in bilayer sheet resistance R{sub s} were monitored as a function of time t{sub a} and temperature T{sub a} during subsequent UHV annealing. Thermal ramping of Al/W and Al/Ti{sub 0.06}W{sub 0.94} bilayers at 3{degree}C min{sup {minus}1} resulted in large ({gt}fourfold) increases in R{sub s} at T{sub a}{approx_equal}550{degree}C, whereas R{sub s} in the Al/Ti{sub 0.33}W{sub 0.67} bilayers did not exhibit a similar increase until {approx_equal}610{degree}C. Interfacial reactions and microstructural changes were followed as a function of annealing conditions. Results indicate that Al/W and Al/Ti{sub 0.06}W{sub 0.94} bilayer reactions proceed along a very similar pathway in which monoclinic WAl{sub 4} forms first as a discontinuous interfacial phase followed by the nucleation of bcc WAl{sub 12} whose growth is limited by the rate of W diffusion, with an activation energy of 2.7 eV, into Al. In contrast, the W diffusion rate during the early stages of Al/Ti{sub 0.33}W{sub 0.67} annealing is significantly higher allowing the formation of a continuous WAl{sub 4} interfacial blocking layer which increases the overall activation energy E{sub a}, still limited by W diffusion, to 3.4 eV and strongly inhibits further reaction. We attribute observed increases in WAl{sub 4} nucleation and growth rates in interfacial Al/Ti{sub 0.33}W{sub 0.67} to a vacancy wind effect associated with the very rapid (E{sub a}=1.7 eV) diffusion of Ti into Al. (Abstract Truncated)
- Research Organization:
- Univ. of Illinois at Urbana-Champaign, IL (United States)
- DOE Contract Number:
- AC02-76ER01198
- OSTI ID:
- 550377
- Journal Information:
- Journal of Applied Physics, Vol. 82, Issue 5; Other Information: PBD: Sep 1997
- Country of Publication:
- United States
- Language:
- English
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