Gas flow sputtering is a sputter deposition method that enables soft and high-rate deposition even for oxides or nitrides at high pressure (in the mbar range). A unipolar pulse generator with adjustable reverse voltage was used to optimize thin film growth by the hollow cathode gas flow sputtering system. In this regard, we describe our laboratory Gas Flow Sputtering (GFS) deposition system, which has been recently assembled at the Technical University of Berlin. Its technical facilities and suitability for various technological tasks are explored. The first experimental efforts are presented by the example of TiOx films on glass substrates obtained at various deposition conditions with forced Argon flow. The influence of pulsing parameters, power, and oxygen gas flow on the plasma generated is studied. The films were characterized by ellipsometry, scanning electron microscopy, x-ray diffraction, and x-ray reflectivity. Optical Emission Spectroscopy (OES) was also used to characterize the remote plasma, and the substrate temperature was measured. The pulsing frequency (f) is a significant factor that provides additional substrate heating by about 100 °C when the plasma regime changes from f = 0 (DC) to 100 kHz. Such a change in frequency provides a significant increase in the OES signals of Ti and Ar neutrals as well as of Ti+ ions. With pulsed operation at high power, the GFS plasma is capable of heating the glass substrate to more than 400 °C within several minutes, which allows for crystalline anatase TiOx film deposition without external heating. For deposition below 200 °C substrate temperature, low power DC operation can be used.

The Hollow Cathode Gas Flow Sputtering (GFS) provides special plasma conditions and is of extensive interest as a more affordable alternative to the high vacuum sputtering techniques. In the case of the tubular cathode a circular outlet symmetry stipulates homogeneity issues for both metallic and reactive deposition regimes. Using the results of Direct Simulation Monte Carlo (DSMC), we propose an external coaxial attachment which is manufactured and examined in a nozzle and a diffuser positioning. The impact on the homogeneity of Ti and ${\mathrm{TiO}}_2$ films is examined using profilometry and spectral ellipsometry. Our results demonstrate that the use of the nozzle attachment significantly enhances film homogeneity from about 3 ${\mathrm{cm}}^2$ to more than 12 ${\mathrm{cm}}^2$. It also secures better process control in terms of oxygen stoichiometry and film thickness. Some crucial general issues of the reactive GFS process are discussed.