Ultrathin Metal Films with Low Resistivity via Atomic Layer Deposition: Process Pressure Effect on Initial Growth Behavior of Ru Films

Because semiconductor devices have become ultraminiaturized, the degradation of conductivity due to the resistivity size effect of metal thin films is an unavoidable problem, and the development of new low-resistivity materials and processes is necessary. Ru thin films are attracting attention as candidate materials for next-generation interconnects. However, it is very difficult to achieve excellent properties in the ultrathin thickness range owing to their initial island growth behavior. We systematically investigated the effect of the process pressure as an important variable for forming ultrathin Ru films with low resistivity by improving the initial growth behavior. Increasing the process pressure reduced the critical size and activation energy for the initial nuclei growth, resulting in rapid continuous thin-film growth through dense and high-density nucleation. Consequently, the resistivity properties of the Ru thin films deposited at high pressures in the sub-5 nm thickness region were significantly improved. In particular, we demonstrated for the first time that a Ru thin film with low resistivity formed continuously at a thickness of sub-2.5 nm, and the method presented in this study can be effectively applied to next-generation metal line processes.