LEEM-PEEM 6 - The 6th International Conference on LEEM-PEEM, Trieste, Italy, 9/7 - 9/11/08

LEEM and LEEM-IV investigations of Pd/Cu(001) surface alloys: surface diffusion, Pd dissolution, and island buckling

Ezra Bussmann (Sandia Nat. Labs), James B. Hannon (IBM Research Div.), Jiebing Sun, Karsten Pohl (UNH), and Gary L. Kellogg (Sandia Nat. Labs)

Ultra-thin films of Pd on Cu(001) are of interest not only as model systems for metal-metal surface alloy formation, but also as potential electromigration inhibitors for Cu interconnect applications [1]. To determine how alloyed Pd affects Cu surface self-diffusion, we are studying the decay of 2-D islands as a function of temperature and Pd concentration. These studies are made possible by previous investigations, in which we determined the distribution of Pd in the top three Cu layers from multiple-scattering-theory fits to LEEM-IV spectra [2]. Here, we use LEEM-IV spectra in a “fingerprinting” mode to monitor the Pd concentration during deposition and island decay. Measurements of decay rates as a function of temperature show that the activation energy for island decay increases from 0.82±0.04 to 0.99±0.06 eV when 0.06 ML of Pd is alloyed into the second layer. Experiments at higher coverages are complicated by the fact that Pd is lost from the second layer at higher temperatures. We are investigating the mechanism of this Pd dissolution, which appears to involve Pd moving laterally into nearby step bunches. In separate experiments, we are investigating the possibility of using LEEM-IV to measure variations in interlayer spacing across Pd/Cu alloy islands, for both islands incorporated into the top Cu layer and islands on top of the surface. Preliminary results indicate that it is possible to extract the spatial variation in concentration and interlayer spacing separately from the LEEM-IV analysis.

[1] C.K. Hu et al., Appl. Phys. Rev. Lett. 81, 1782 (2002)

[2] J.B. Hannon, J. Sun, K. Pohl, and G.L. Kellogg, Phys. Rev. Lett. 96, 246103 (2006)

*Work performed at Sandia was supported by the U.S. DOE, Office of BES, DMSE. Sandia is operated by Sandia Corporation, a Lockheed Martin Company, for the U. S. DOE’s NNSA under Contract No. DE-AC04-94AL85000. Work at UNH was supported by the NSF under Grant No. DMR-0134933.