Thin films of many different materials are in high demand for a wide range of industrial applications. Thanks to their diverse properties it is possible to create products with functional properties that were previously impossible. In recent years, scientists have developed a wide range of technologies that enable to deposit different thin films on different substrates. However, for successful industrial applications, the developed technology must be able to produce coatings in the required quality, with enough high deposition rate and at an affordable price.
A typical example of a desired but unavailable technology is high-rate sputtering of oxide layers such as titanium dioxide - TiO2. Current technologies can deposit such films either slowly (and well) or quickly (and poorly). In the frame of our three-year project, we managed to develop a new technology that combined both positive properties (speed and quality) together.
This technology is based on the principle of hollow cathode discharge, which has been known for decades. A discharge is ignited inside the hollow metallic cathode causing the incident argon ions to eject atoms from the cathode surface, which are carried by the flowing gas towards the substrate. In contrast to classical reactive magnetron sputtering, in this case, the cathode cannot be oxidized and thus the deposition rate cannot slow down because oxygen is injected into the chamber by a different inlet than argon. To achieve an even higher deposition rate, we placed a part of the hollow cathode outside the copper cooler. This causes an extreme increase in the temperature of the hollow cathode, which results in thermal evaporation of the individual atoms from its surface. By combining plasma sputtering with thermal evaporation, the deposition rate can be increased several times.
The main disadvantage of this technology is the significant inhomogeneity of the deposited films caused by the geometry of the whole process. In order to be able to apply coatings to large areas, we have developed a multi-plasma-jet system with several parallel hollow cathodes, as shown in Figure 1. The homogeneity of deposited films is guaranteed by feedback control of the temperature of each nozzle. Since this system originated partly from business cooperation, we protected the principle of regulation of homogeneity and the completely developed system by Czech and international patent [1]. At present, the developed system is mainly used for scientific purposes and for the preparation of thin or thick films of various hardly obtainable oxides. One of the possible applications was recently described in our last publication [2]. Several industrial partners have already expressed their interest in this technology. Currently, we are discussing license conditions with them.
References:
[1] J. Olejnicek, J. Smid, Z. Hubicka, P. Adamek, M. Cada, S. Kment (2018) A Method for Controlling the Deposition Rate of Thin Films in a Vacuum Multi-Nozzle Plasma System and a Device for Performing of the Method, int. p. number: WO 2018/059609 A8,
[2] J. Olejnicek, J. Smid, R. Perekrestov, P. Ksirova, J. Rathousky, M. Kohout, M. Dvorakova, S. Kment, K. Jurek, M. Cada, Z. Hubicka: Co3O4 thin films prepared by hollow cathode discharge, Surf. Coat. Technol. 366 (2019) 303-310.
Figure 1: Schematic picture of a multi-jet deposition system using the hot hollow cathodes for high-rate deposition of oxide films.
Figure 2: Photo of a burning discharge and hot titanium cathodes whose temperature can reach up to 1600 ° C. The bottom part of the figure shows the principle of homogenization of the film when sputtering is performed from several nozzles simultaneously.
