Electrolessly deposited diffusion barriers for microelectronics

Electrolessly deposited materials were investigated as possible diffusion barrier layers for multilayer microelectronic structures. Attention was focused on selective deposition of barrier layers on various surfaces, the barrier's capability to inhibit Cu diffusion, changes in Cu resistivity caused by barrier material diffusion into Cu, and adhesion between a polyimide film and the barrier layer. Electroless Co(P) was the most effective barrier to Cu diffusion at elevated temperature, even at Co(P) thicknesses as low as 500 Å. Diffusion-barrier effectiveness of electrolessly deposited materials decreased in the following order: Co(P) > Ni-Co(P) ≃ Ni(P) ≫ pure metals Co, Ni). Although a polyimide film bonded strongly to electrolessly deposited Ni(P) layers and only weakly to as-deposited Co(P), electroless Ni(P) significantly increased the Cu resistivity through interdiffusion. Polyimide adhesion to Co(P) was improved by oxidizing a Co(P) surface immediately after deposition to grow a passive film 50–75 Å thick, yielding a surface to which the polyimide adheres strongly and reproducibly. A low-energy-beam, scanning electron microscopy/energy-dispersive X-ray analysis technique (SEM/EDX) was developed to measure the nonoxidized thin Co(P) barrier layer thickness.