Low-energy ion irradiation in HiPIMS to enable anatase TiO₂ selective growth

High power impulse magnetron sputtering (HiPIMS) has already demonstrated great potential for synthesizing the high-energy crystalline phase of titanium dioxide (rutile TiO₂) due to large quantities of highly energetic ions present in the discharge. In this work, it is shown that the metastable anatase phase can also be obtained by HiPIMS. The required deposition conditions have been identified by systematically studying the phase formation, microstructure and chemical composition as a function of mode of target operation as well as of substrate temperature, working pressure, and peak current density. It is found that films deposited in the metal and transition modes are predominantly amorphous and contain substoichiometric TiO_x compounds, while in compound mode they are well-crystallized and present only O²⁻ ions bound to Ti⁴⁺, i.e. pure TiO₂. Anatase TiO₂ films are obtained for working pressures between 1 and 2 Pa, a peak current density of ∼1 A cm⁻² and deposition temperatures lower than 300 °C. Rutile is favored at lower pressures (<1 Pa) and higher peak current densities (>2 A cm⁻²), while amorphous films are obtained at higher pressures (5 Pa). Microstructural characterization of selected films is also presented. (paper)