Kinetics of Ag/Al bilayer self-encapsulation

The self-encapsulation kinetics of Ag/Al bilayers were studied both experimentally and theoretically as part of the effort to introduce Ag as an alternative metallization scheme for future ultra-large-scale-integrated technologies. Theoretical modeling was based on an analytical solution of a modified diffusion equation, which incorporated the diffusion of Al atoms through the Ag layers during the Ag/Al bilayer encapsulation progress. The amount of segregated Al atoms was monitored by both Rutherford backscattering spectrometry and film resistivity measurements, and correlated well with the theoretical predictions. These findings showed that the kinetics of the self-encapsulation could be significantly affected by both (i) the chemical affinity between Al and Ag atoms, and (ii) the interfacial energy between the metal layer (Ag) and the newly formed ${\mathrm{Al}}_x{\mathrm{O}}_y{\mathrm{N}}_z$ diffusion barriers. Higher anneal temperatures were shown to accelerate the encapsulation process, and hence, achieved a lower resistivity in the underneath Ag layer. This model, in addition, confirmed the self-passivating characteristics of ${\mathrm{Al}}_x{\mathrm{O}}_y{\mathrm{N}}_z$ diffusion barriers formed by Ag/Al bilayers annealed between 500 and 725 $°$ C.