Anomalous properties found in Cu films near below 100 nm thick deposited on Ta

For the Cu films sputter-deposited at ambient temperature on a Ta buffer layer with a clean surface (the ex-Cu film) and those on a Ta buffer layer with native oxide (the ex-Cu film), the internal stress along the film surface, σi||, the Young’s modulus, Ef, the internal friction, , the decrease in after annealing at 400 K, , and the root mean square of surface roughness (the RMS roughness) were studied for the Cu film thickness, tCu, between 5 and 1000 nm. For the ex-Cu films with tCu below 100 nm, Ef showed a deviatory decrease from its theoretical value, Ef,th, which was estimated from the crystallographic texture and σi||, suggesting that the constituent static anelastic strain due to grain boundaries (GBs), εsa,GB, was, e.g. as large as about 25% of the constituent elastic strain, εe, at tCu of 10 nm. The local maximum of the RMS roughness and the local minimum of were found near below 100 nm, indicating that the properties of GBs in already deposited Cu film were modified by additional deposition (the capping effect, below) and the anomalous capping effects took place near below 100 nm in tCu. For the ex-Cu films, Ef showed good agreement with Ef,th except that a local decrease in Ef was found for tCu near below 100 nm. The local maxima of and the RMS roughness were found for tCu near below 100 nm too. It is suggested that the properties of GBs in the ex-Cu films were of those in bulk metal for tCu below a few tens of nanometer and then changed to those in nanocrystalline metal with increasing tCu. The capping effects were also observed for the ex-Cu films.