Three-step deposition process for improved nucleation of noble metal thin films

A new three-step atomic layer deposition process has been found to produce more evenly distributed ruthenium thin films that are also largely free from oxygen impurities. In studying how oxygen affected nucleation, researchers found that an additional hydrogen pulse could dramatically improve film deposition.

Ruthenium thin films, with high work functions and low bulk resistivity, are gaining attention for applications in nanotechnology. Traditionally, atomic layer deposition process uses a ruthenium precursor and oxygen gas pulses to deposit the ruthenium. However, the nucleation is a long process that often results in island-like ruthenium distributions, which makes them inferior for nanotechnology applications.

“While atomic layer deposition is known for its layer-by-layer growth, it is quite hard to control the thickness when depositing thin metal films because of the formation of islands,” said co-author Adriaan Mackus. “With this work, we hope to contribute to solving this challenge.”

The new method adds a hydrogen pulse to reduce the oxides formed on the metallic film. This allows longer oxygen pulses to be used, which makes for faster nucleation and smoother films.

The ruthenium films created with the new process were tested for a multitude of characteristics, including electrical resistivity, composition, surface morphology and nucleation behavior.

Previously, the researchers developed a similar three-step atomic layer deposition process for platinum. Given the new results, the researchers believe that the benefits of this process could be reproduced for many other noble metals. Ultimately, this could widen the use of ruthenium thin films for use in nanoelectronics.

Source: “Atomic layer deposition of ruthenium using an ABC-type process: Role of oxygen exposure during nucleation,” by Sonali N. Chopra, Martijn F. J. Vos, Marcel A. Verheijen, John G. Ekerdt, Wilhelmus M. M. Kessels, and Adriaan J. M. Mackus, J. Vac. Sci. Technol. A (2020). The article can be accessed at https://doi.org/10.1116/6.0000434 .