Study of diffusion barriers for microelectronics
Motivation and results
The ultra large scale integration (ULSI) in microelectronic devices has led to the introduction of copper as metallization material as it has a lower electric resistivity and a better resistance against electromigration compared to Al used previously. However, copper diffuses rapidly into silicon and drifts through SiO2 under applied voltage, which may cause device failures. Therefore a diffusion barrier layer between the wiring material and the surrounding material is necessary.
Tantalum-based materials are mostly used today as barrier material, however, beside Ta especially Ti and W have been discussed also as possible candidates. Ta, TaN, Ti and TiN films were deposited by magnetron sputtering onto Si and SiO2 with thicknesses of less than one monolayer up to some nm. The samples were transferred after deposition immediately into the analysis chamber without breaking the vacuum to avoid oxide and contamination formation. Analysis was done by means of X-ray photoelectron spectroscopy (XPS) for elemental and bonding state characterization and angle resolved XPS (ARXPS) for non-destructive depth profiling. The XPS measurements showed different phase formation processes at the interfaces: silicides, oxides and nitrides are formed depending on the materials combination. Based on such chemical observations layer models for quantification of ARXPS measurements with appropriate calculation procedures were derived, so it was possible to obtain information on the surface and interface morphology.
W and WN will be studied to complete the knowledge on the growth of the barrier candidates. Investigations on low-k dielectric material are planned for the future.
M. Zier, S. Oswald, R. Reiche, K. Wetzig, XPS investigations of thin tantalum films on a silicon surface, Anal. and Bioanalyt. Chem. 375  (2003) 902-905 (doi:10.1007/s00216-003-1788-2).
M. Zier, S. Oswald, R. Reiche, M. Kozlowska, K. Wetzig, Interface Formation and Reactions at Ta-Si and Ta-SiO2 interfaces studied by XPS and ARXPS, J. Elect. Spect. Rel. Phenom. 137-140 (2004) 229-233 (doi:10.1016/j.elspec.2004.02.060).
M. Zier, S. Oswald, R. Reiche, K. Wetzig, XPS and ARXPS Investigations of ultra thin TaN films deposited on SiO2 and Si, Appl. Surf. Sci. 252  (2005) 234-239 (doi:10.1016/j.apsusc.2005.02.025).
W. Zahn, D. Hildebrand, S. Menzel, S. Oswald, H. Heuer, Characterization of thin Ta-Si-Nx layers of different nitrogen content using XPS, UPS and STM, Appl. Surf. Sci. 252  (2005) 89-93 (doi:10.1016/j.apsusc.2005.02.043).