Thin-film interdiffusions in Cu/Pd, Cu/Pt, Cu/Ni, Cu/NiB, Cu/Co, Cu/Cr, Cu/Ti, and Cu/TiN bilayer films: Correlations of sheet resistance with Rutherford backscattering spectrometries

Abstract

Interdiffusion in the Cu-based Cu/Pd, Cu/Pt, Cu/Ni, Cu/NiB, Cu/Co, Cu/Cr, Cu/Ti, and Cu/TiN bilayer films has been investigated for anneal temperatures ranging from 150 to 400 °C in forming gas (N2-10%H2). The diffusion of Pd, Pt, and Ni into Cu has resulted in a significant increase in the sheet resistance of the film, which is correlated with the concentration profiles obtained from Rutherford backscattering spectrometries. In contrast, the diffusion of Co or Cr into Cu is negligible, probably due to the lack of solubility of Co or Cr in Cu at temperature ≤400 °C. Outdiffused Cu species were detected on the Pd, Pt, Ni, NiB, Ti, and Co surfaces, while that of Cu through Cr or TiN was negligible. The increases in film resistivities are mostly due to the increase of electron-impurity scattering centers as solute atoms diffuse into Cu. As a result, factors such as the use of different overcoated metals, annealing temperature, thickness of the Cu film, and the grain size of Cu all played a critical role in affecting the resistivity of the Cu films. The driving force for interdiffusion in these binary systems appears to be dominated by the mutual solubility between the bilayer films. Interdiffusion between the bilayer films can be suppressed by interposing a diffusion barrier layer of Cr, Ti, Zr, or TiN between Cu and the overcoated films. The trilayer structures are thermally stable up to 400 °C.