Comparative Study of Ionized Metal Plasma Ta, TaN and Multistacked Ta/TaN Structure as Diffusion Barriers for Cu Metallization

The properties of the ion-metal-plasma (IMP) deposited Ta, TaN and multistacked Ta/TaN between Cu and SiO2 have been investigated in the Cu/barrier layer/SiO2/Si structures using four-point probe, atomic force microscopy (AFM), X-ray diffraction (XRD), Rutherford back scattering (RBS), tunneling electron microscopy (TEM) and metal-pulse techniques. It was found that the multistacked Ta/TaN barrier shows the best metallurgical and thermal stability among three of them, and the superior stability is found to result mainly from the nanocrystalline microstructure rather than the density and grain size of the barrier materials. The microstructure, which contains nanocrystalline grain and amorphous-like matrix, can better retard the intermixing and diffusion of Cu, Ta, O and Si atoms, due likely to reduction of grain boundaries that are the main passway for the diffusion of these elements.