Thermal coefficient of resistivity of ultrathin Ag films deposited on Cu for applications in emerging interconnect systems

Abstract

As the semiconductor industry continues to scale feature sizes, scattering from phonons, surfaces, and grain boundaries results in a significant increase in metal interconnect resistivity. In this work, a thin Ag capping layer is used to modify electron–phonon scattering in 20 nm Cu films to reduce the total resistivity of the bilayer system. To investigate the effect of Ag layer thickness on the electrical properties of the underlying Cu film, the thermal coefficient of resistivity (TCR) is calculated for Cu films that are capped with ultrathin Ag layers of various thicknesses. The TCR exhibited a dependence on the thickness of the ultrathin Ag films deposited on Cu. The slope of the resistance versus temperature is lower for Ag-capped Cu films when compared to bare Cu films. A reduced thermal coefficient of resistivity combined with a lower room temperature resistivity for Ag/Cu films is consistent with a decreased contribution of the temperature dependent portion of the resistivity to the total resistivity, which may prove critical for the viability of future metal-based interconnect architectures.