Thin electroless barrier for copper films

Electroless barrier deposition for copper metallization potentially provides many advantages, among which are the selectivity to dielectrics, possibility of an amorphous alloy deposition, binary alloy properties enhancement by an addition of a third component, high conformity and low cost. Electroless cobalt-rich CoWP ternary alloys with high phosphorus content (∼11 weight percent) and a low weight percent of the third component, tungsten (∼ 2 percent), were deposited in basic solution onto copper and cobalt in integrated circuit structures. A capability of the electroless CoWP deposition to form thin selective and conformal barrier/protection films was demonstrated. Extendibility of these thin films to extremely small, nano-scale dimensions was observed. Conformal 10 nm thick CoWP layer was formed on the sidewalls of 30-40 nm wide seam of aspect ratio about 5:1 on the top of 0.4 μm wide in-laid Cu line. Thermal stability of electroless CoWP / Cu films investigated by Rutherford Backscattering Spectroscopy (RBS), Auger Electron Spectroscopy (AES) and Secondary Ion Mass Spectroscopy (SIMS) was extended to 500°C for 15 nm thick barrier. Atomic Force Microscopy (AFM) images of the electroless CoWP film surface and sectional analysis showed small grain sizes of CoWP on either electroless or Physical Vapor Deposited (PVD) Cu films. Several passivation schemes to protect the exposed Cu surface and adhesion promotion/barrier layers to stabilize the Cu/dielectric interface in a damascene process were demonstrated.