Carbon-doped Cu films with self-forming passivation layer

It was previously known that C-doping in Cu effectively enhances the film thermal stability and maintains a low electrical resistivity even upon high-temperature annealing, via a diffusion inhibiting the mechanism of C-stabilized oxide interlayer between Cu and Si. In the present work, the stability and resistivity are investigated in two Cu films doped with more C, respectively 2.9 at.% and 4.2 at.% as measured by EPMA. As expected, the thermal stability is even further enhanced, without significantly affecting the resistivity. After a systematic microstructural investigation by TEM, it is revealed that the relevant mechanism lies both in the enhanced stability via C dissolution in the silica native oxide layer at the Cu/Si interface and in the C-passivated Si surface zone beneath the layer. In the 4.2% C film, the Cu/Si interaction is mainly inhibited by self-forming SiC nano-particles and the resistivity remains below 3 μΩ·cm even upon annealing at 500 °C for 40 h. The C-doping can then be a simple process route towards manufacturing stable Cu interconnects.