Investigation of dielectric/metal bilayer sidewall diffusion barrier for Cu/porous ultra-low-k interconnects

A dielectric/metal bilayer structure of a-SiC:H/Ta was integrated and investigated for application as a sidewall diffusion barrier in a Cu/porous ultra-low-k interconnect structure. Different dielectric/metal bilayer thicknesses were investigated. The electrical tests and physical analyses indicate that this a-SiC:H/Ta bilayer structure is a more efficient sidewall diffusion barrier than the conventional physical vapor deposited (PVD) multistack TaN/Ta metal barrier. With a similar total sidewall barrier thickness, an even better barrier integrity and reliability can be achieved by using a thicker a-SiC:H layer and a correspondingly thinner Ta barrier. This achievement is mostly attributed to the surface modification and sealing of the porous ultra-low-k surface by the a-SiC:H layer. Thus, the scenario of the barrier failure due to defects in the Ta (or TaN) barrier layer directly deposited on rough porous ultra-low-k material is avoided. Bias-temperature stress (BTS) and time-to-failure (TTF) studies indicate the Copper penetration through the sidewall barrier into the porous dielectric was the dominating failure mechanism in the conventional PVD TaN/Ta barrier and bilayer barrier of thinner a-SiC:H (14 Å) and thicker Ta (71 Å) layers, although the latter enhanced the lifetime of interconnect structures considerably. The bilayer barrier consisting of a thicker a-SiC:H (60 Å) and correspondingly thinner Ta (53 Å) layers was more robust to protect the sidewall region so that this sidewall Cu diffusion induced failure mechanism was no longer found in Cu/porous ultra-low-k interconnect structures even after thermal stress at 200°C for 120 h.