Tantalum-microcrystalline CeO₂ diffusion barrier for copper metallization

A tantalum diffusion barrier incorporating microcrystalline CeO₂ is proposed for Cu metallization and investigated using Auger electron spectroscopy, x-ray diffraction, optical microscopy, transmission electron microscopy, and sheet resistance measurements. The Cu/Ta+CeO₂/Si contact system retained its structure up to 800°C without an increase in resistivity. The cerium dioxide (CeO₂) was stuffed along the grain boundaries during the deposition of Ta layer. Because of its heavier atomic weight than O₂- or N₂-stuffed elements, it inhibited an interdiffusion of Cu and Si through grain boundaries which can act as fast diffusion paths. It also resulted in preventing the outdiffusion of Ta into the overlayer Cu as well as suppressing the formation of Ta suicide up to 800°C. It appears that the barrier properties of the tantalum incorporating microcrystalline CeO₂ are superior to polycrystalline transition metal barriers, polycrystalline nitride barriers, ternary amorphous compound barriers, and N₂- and O₂-stuffed barriers.