Characterization of Plasma-Induced Atomic Diffusion in Thin Films

Plasma-material interaction is important in different fields ranging from plasma-assisted green chemistry to materials processing like plasma-etching used during fabrication of nano-electronics.
Metallic thin films improve the heat emissivity, which is essential for preventing fracturing of fragile substrates like thin freestanding silicon nitride membrane exposed to high heat loads [1]. Ruthenium is frequently used as emissivity layer, since it only forms native oxide of <1 nm and has good potential to resist reactive plasma environments.
Heat emissivity performance is influenced by thin film morphology. However, the atomic scale morphological change of plasma-exposed thin films is barely reported [2]. Our research presents first observations of hole formation in ruthenium thin films treated by a nitrogen plasma.
Transmission electron microscopy (TEM) provides sub-nm resolution and in combination with custom-made electron transparent Si3N4 membranes it represents an ideal method to study plasma-thin film interaction.
Depending on the film structure, we observed an initial improvement of film coverage followed by plasma-induced hole formation, including details like growth and merging of holes. Dictating driving forces for these processes might originate from surface energies of crystal facets and the bonding state of individual atoms [3].
With the acquired knowledge, we improved understanding on atomic scale plasma interactions, pushing our knowledge beyond boundaries previously known.

References
[1] van Zwol et al. J. Appl. Phys. 118, 213107 (2015)
[2] Kwon et al. J. Nanosci. Nanotechnol. Vol. 13, 6109-6114 (2013)
[3] Jang et al. J. APL Mater. 3, 126103 (2015)