Characteristics of Atomic Layer Deposited Molybdenum Carbonitride Films

Abstract

As memory devices have recently been scaled down, the design rule of dynamic random access memory (DRAM) approaches 15 nm, which causes problems related to the resistivity size effect. The resistivity size effect is a phenomenon in which electron scattering and the resistance rapidly increases as metals such as copper and tungsten are scaled down to nanoscale. Due to the low resistivity and barrier characteristics, there has been a great interst in molybdenum-based materials for a metal gate word line, interconnects, diffusion barrier, etc. For these applications, it is most important to select a process that can control the roughness and thickness of the film. Although chemical vapor deposition (CVD) is still mainly used and has advantages in that the high deposition rate, it is difficult to control the thickness. Moreover, CVD has relatively low step coverage and high impurity contents. On the other hand, the atomic layer deposition (ALD) process has an insignificant impurity content, and thickness control is advantageous. In addition, since it has excellent uniformity and step coverage, a thin film with excellent conformality can be obtained regardless of structure. In this study, MoCxNy films were deposited using conventional thermal ALD and double-reactant ALD techniques with new liquid Mo precursor. Using the double-reactant ALD technique, MoCxNy thin film with less impurities was deposited by reacting with NH3 gas after removing the ligand due to an intermediate H2 exposure. Auger electron spectroscopy (AES) showed the atomic concentration of MoCxNy, and it showed that the oxygen of the deposited thin film with double-reactant ALD was less than that of the conventional thermal ALD deposited thin films. The ratio of Mo and C of both thin films was almost the same, but the oxygen of the MoCxNy film deposited by the double-reactant ALD was reduced to about 1%. In the case of conventional thermal ALD, the lower the deposition temperature, the more impurities remained. The reason is that sufficient thermal energy was not supplied to completely remove the ligand. The thickness of MoCxNy films were measured by scanning electron microscopy (SEM) and 4-point probe analysis was performed to measure the sheet resistivity of the film. Through the double-reactant ALD, the resistivity was improved from 700-780 μΩ·cm to 460-540 μΩ·cm, confirming that it was a low-resistivity film. Furthermore, we demonstrate that the MoCxNy film can serve as a diffusion barrier up to 600℃.