Researchers take a close look at the chemical reactions in the production of thin films on moving polymer substrates

From integrated circuits and batteries to mirrors and antireflective coatings, functional thin films play an integral part in many devices. With ever-increasing demand for thin films, manufacturers need high-throughput deposition processes that control thickness, density and morphology. Dielectric barrier discharge meets these requirements and can be operated at atmospheric pressure for large-scale manufacturing. Using two electrodes and two dielectric barriers, a plasma is generated to deposit thin films on moving substrates.

To better understand the deposition process, researchers at the Dutch Institute for Fundamental Energy Research, Eindhoven University of Technology, and FUJIFILM Manufacturing Europe B.V. measured the chemical reactions that occur when using a dielectric barrier discharge. They published these findings in Journal of Applied Physics.

Using a Fourier transform infrared spectrometer, the scientists conducted measurements of the plasma exhaust gas in an open-air roll-to-roll deposition system. The discharge was ignited between two copper electrodes covered by polymeric substrates as dielectrics.

Both nitrogen-related species (HNO₂, N₂O, NO₂, NO) and carbon-related species (HCOOH, CO, CO₂) were identified in the absorption features of the plasma. The researchers observed strong plasma-polymer interactions in precursor-free oxygen-containing gas mixtures, as evidenced by high CO_x production.

Also, the addition of tetraethylorthosilicate (TEOS) as a precursor caused variable changes in CO_x production. At high precursor flows, the production of CO_x is dominated by precursor dissociation. However, much lower precursor flows tip the balance of the process towards polymer etching.

With this understanding of the gas phase chemical processes, the group hopes to continue research to enhance throughput and improve the resulting thin film properties.

Source: “Infrared gas phase study on plasma-polymer interactions in high-current diffuse dielectric barrier discharge,” by Y. Liu, S. Welzel, S. A. Starostin, M. C. van de Sanden, Richard Engeln, and Hindrik de Vries, Journal of Applied Physics (2017). The article can be accessed at https://doi.org/10.1063/1.4985619 .