An investigation into the performance of diffusion barrier materials against copper diffusion using metal-oxide-semiconductor (MOS) capacitor structures

Cu/SiO 2/Si capacitors were fabricated, with and without barrier layers between the copper and the oxide, and the dielectric properties of the 100 nm thermal SiO 2 layers monitored after high temperature stressing. Film properties were also examined by X-ray diffraction spectroscopy (XRD) and atomic force microscopy (AFM). Diffusion barriers of Ti, TiN, TiN/Ti, Ta and TaN/Ta were assessed for thermal stability and ability to prevent Cu diffusion. These evaluations indicated that a 10 nm PVD TiN film is a good barrier against Cu diffusion up to 550°C, whilst the addition of a thin Ti layer allows the TiN barrier to withstand a 600°C 60 s anneal. Ta and its nitrides were assessed and found to fail at temperatures as low as 400°C.