Passivation of Cu by sputter-deposited Ta and reactively sputter-deposited Ta-nitride layers

Sputter-deposited tantalum (Ta) and reactively sputter-deposited Ta-nitride films were studied with respect to the passivation capability against copper (Cu) oxidation in thermal O-2 ambient. A 200 Angstrom Ta or Ta-nitride film was sputter-deposited on a 2000 Angstrom Cu film using a Ta target in an Ar/N-2 gas mixture. With Ta passivation, Cu was not oxidized at temperatures up to 400 degrees C, which can be further improved by using passivation of an amorphous Ta-nitride film deposited in an appropriate condition. The absence of long-range defects in the Ta-nitride film was presumably responsible for this improvement. However, sputtering-induced surface damage by excess N-2 in the sputter gas mixture may reduce the passivation capability of Ta-nitride films. When the passivated Cu was oxidized, the Cu oxides always resided in the top sur face region. That is, in the oxidation process, Cu diffused through the defects of the passivation layers to the outer surface.