Copper ion drift in integrated circuits: Effect of boundary conditions on reliability and breakdown of low-k dielectrics

Abstract

Copper drift in current interconnect structures is a reliability issue leading to premature low-k dielectric breakdown. Copper ions drift through insulating low-k dielectrics leading to an increase in the local electric field that, if high enough, could lead to device failure. We have solved the coupled continuity and Poisson’s equation using the boundary condition that the flux of copper ions equals zero [J(t,L)=0] at the cathode or dielectric-semiconductor interface. This condition closely mirrors the actual physics in interconnects and leads to a buildup or accumulation of copper ions at the dielectric-semiconductor interface. Significant differences are observed in the copper concentration and local electric field behavior near the interface when the condition of a blocking electrode [J(t,L)=0] compared to the concentration equals zero [C(t,L)=0] with implications for the reliability of the low-k dielectric and time to failure for the interconnect structure. The time to failure (TTF) is shown to depend on the boundary condition at the cathode Ce, the copper ion solubility in the dielectric, as well as the drift of copper ions through the dielectric. When intrinsic thermal effects are included in addition to the mass transport, a close fit is achieved with experimental TTF results of Hwang et al. [J. Appl. Phys. 101, 074501 (2007)] The inclusion of mass transport simulates the nonlinearity in TTF at low fields, a characteristic that has been observed experimentally.