Resistance Decay of Cu/Porous Low- ${k}$ Interconnect: Modeling and its Impact on Electromigration

Abstract

It was found previously the resistance of Cu interconnect ( ${R}$ ) could decrease during baking and acceleration test, owing to moisture invasion through the nanoporous low- ${k}$ followed by moisture-induced oxidation of Ta-based liner and specularity recovery of the electron scattering at Cu/Ta interface. In this paper, a model is established to quantitatively interpret the underlying kinetics. It is shown that the model fits well with the experimentally observed hump-shaped temperature dependence of the R decay rate of Cu/porous SiCOH interconnects at 28-nm node at 170 °C~350°C. It reveals that the liner oxidation and resistance decay are controlled mainly by the migration of metal cation through the as-oxidized liner at the low temperatures but by the desorption/diffusion of the chemisorbed moisture in the low- ${k}$ at the high temperatures. Particularly, the model well reproduces the modest and unexpectedly significant low- ${k}$ -thickness dependence of the decay rate at the low and high temperatures, respectively, which indicates clearly the temperature-dependent influence of the tortuous diffusion path of moisture in the porous low- ${k}$ . The intimate relationship of Cu electromigration performance to such ${R}$ decay is also demonstrated.