Effects of annealing and interlayers on the adhesion energy of copper thin films to SiO₂/Si substrates

The adhesion of sputtered copper thin films was measured with a quantitative indentation technique utilizing refractory superlayers to trigger and promote delamination. Adhesion energies of the indentation-induced delaminations were analyzed in terms of the critical strain energy release rate. Two groups of films were investigated. Group I ranged in thickness from 225 to 1000 nm in both the as-deposited and annealed condition. Adhesion energies ranged from 2 to 15 J/m², with higher adhesion for the annealed condition. Group II films had nominal thicknesses of 430 and 1100 nm, some with 7-10 nm interlayers of either titanium or chromium. Adhesion energies of these films ranged from 4 to 30 J/m², increasing by a factor from 1.3 to 7.5, as a function of the interlayer presence and type, with the increase in energy due to a chromium interlayer exceeding that of titanium. Adhesion energies increased with film thickness for all films, with interlayers and annealing producing a larger increase. These quantitative results were compared to previous semi-quantitative and quantitative results, and shown to have comparable magnitudes and trends.