A BEOL multilevel structure with ultra low-k materials (k ≤ 2.4)

A multilevel back-end-of-line structure with a dielectric constant κ ≤ 2.4 ultra low-κ materials was developed. κ=2.2 ULK build was demonstrated at a 144nm wiring pitch and a κ=2.4 ULK was demonstrated at a 288nm pitch. Good model-to-hardware correlation for the measured capacitance indicated no significant plasma damage to the ULK 2.2 material. The extracted copper resistivity was consistent with size-effect predictions of an electron scattering model. An optimized SiN/SiC_xN_yH bilayer copper cap scheme was developed to minimize low-κ damage. Also, an alternative CoWP metal cap, for improved electromigration resistance, is discussed. Preliminary TDDB reliability testing suggests V_bd of ULK 2.2 144nm pitch structures and ULK 2.4 288nm pitch structures was comparable to that of dense low-κ films at similar pitches, with very few extrinsic fails.