Grain growth and void formation in dielectric-encapsulated Cu thin films

Grain growth in 40-nm-thick Cu films encapsulated by over- and under-layers Of SiO2, Al2O3, Si3N4, and MgO was investigated. The films were magnetron sputter deposited onto cooled SiO2/Si substrates in an ultrahigh vacuum purity environment. Ex situ annealing was performed at 400 and 800 degrees C in 1 atm reducing gas. Films deposited at -120 degrees C exhibited more extensive grain growth after annealing than films deposited at -40 degrees C. Films annealed at room temperature had grain sizes less than 35 nm. All films exhibited some void formation after annealing at 400 and 800 C, but the films encapsulated in Al2O3 exhibited the lowest area fraction of voids. The mean grain sizes of the Al2O3-encapsulated films, as measured by the linear intercept method, were 86 and 134 nm after annealing at 400 and 800 degrees C, respectively.