Correlation between the early stage of copper metal organic chemical vapor deposition and the material properties of thin film

Abstract

Cu metal organic chemical vapor deposition has been performed on TiN/Si(100) substrates using Cu(I)(hfac)(vtms) at various substrate (110⩽Ts⩽300 °C) and bubbler temperature (0⩽Tb⩽30 °C) conditions, in which the early stage of film formation characterized by scanning electron microscopy and in situ laser beam (λ=6328 Å) reflectance measurement could be well correlated with the surface roughness and the electrical resistivity of the copper films developed in a later stage. All the reflectance versus deposition time curves showed a qualitatively similar shape consisting of three sequential parts: a rapid initial decrease to a minimum, an increase to a maximum, and a gradual decay to almost zero, in which the minimum and maximum roughly correspond to the onset and completion of island coalescence, respectively. As the Ts is raised and/or the Tb is lowered, larger islands were formed in a smaller density at the onset of island coalescence due to a lower nucleation rate. The surface roughness gradually develops with increasing film thickness after forming a continuous film, but it does not saturate at a thickness of ∼2 μm and shows a correlation with the average island size in the earlier coalescence stage, i.e., the smaller islands evolves to a smoother surface. Above the threshold temperature (Ts∼230 for Tb=30 °C) the copper islands begin to show facets and at even higher Ts large truncated polyhedron-shaped copper islands are formed, which upon coalescing leave many interfacial voids to result in a film with a very rough surface and a high electrical resistivity. The copper films deposited at 150⩽Ts⩽200 °C have a very low value of ρ≈2 μΩ cm, which increases by a factor of ∼2 when Ts is lowered to 110 °C. The latter was accompanied by the formation of smaller islands at the onset of coalescence, and therefore the increase in ρ at Ts⩽150 °C was attributed to the electron scattering at the grain boundaries.