AL TIXW1-X METAL/DIFFUSION-BARRIER BILAYERS - INTERFACIAL REACTION PATHWAYS AND KINETICS DURING ANNEALING/

Polycrystalline bcc TixW1-x layers with mixed 011 and 002 texture were grown on oxidized Si(001) substrates at 600 degrees C by ultrahigh-va cuum (UHV) magnetron sputter deposition from W and Ti0.33W0.67 targets using both pure Ar and Xe discharges. Ti concentrations in the 100-nm -thicle layers were 0, 6, and 33 at. % depending on target composition and sputtering gas, Al overlayers, 190 nm, thick with strong 111 pref erred orientation, were then deposited in Ar at 100 degrees C with and without breaking vacuum, Changes in bilayer sheet resistance R-s were monitored as a function of time t(alpha) and temperature T-alpha duri ng subsequent UHV annealing. Thermal ramping of Al/W and Al/Ti0.06W0.9 4 bilayers at 3 degrees C min(-1) resulted in large (>fourfoId) increa ses in R-s at T(alpha)similar or equal to 550 degrees C, whereas R-s i n the Al/Ti0.33W0.67 bilayers did not exhibit a similar increase until similar or equal to 610 degrees C, Area-averaged and local interfacia l reactions and microstructural changes were also followed as a functi on of annealing conditions. The combined results indicate that Al/W an d Al/Ti0.06W0.94 bilayer reactions proceed along 3 very similar pathwa y in which monoclinic WAl4 forms first as a discontinuous interfacial phase followed by the nucleation of bcc WAl12 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 0.33W0.67 annealing is significantly higher allowing the formation of a continuous WAl4 interfacial blocking layer which increases the overa ll activation energy E-alpha, still limited by W diffusion, to 3.4 eV and strongly inhibits further reaction. We attribute observed increase s in WAl4 nucleation and growth rates In interfacial Al/Ti0.33W0.67 to a ''vacancy wind'' effect associated with the very rapid (E-alpha=1.7 eV) diffusion of Ti into Al. (C) 1997 American Institute of Physics.