Nb-doped TiO2 coatings developed by high power impulse magnetron sputtering-chemical vapor deposition hybrid deposition process

Novel methods for the deposition of thin functional coatings, such as hybrid physical vapor deposition-chemical vapor deposition (CVD) technologies, have the potential to become an important means of overcoming the limitations of current processes, such as low deposition rates, associated with some sputtering processes, or limited material/precursor choices, associated with CVD processes. This work explores the potential of addressing these issues through the development of a hybrid system, which combines the latest magnetron sputtering technology, high power impulse magnetron sputtering (HiPIMS), with plasma enhanced chemical vapor deposition (PECVD) technology. This system seeks to overcome the limitations of each technique and provide a new, flexible deposition tool for functional films, such as transparent conductive oxides. In this system, the plasma generated by the magnetron provides a source of electrons to drive the CVD precursor decomposition and reaction chemistry in the PECVD process. Consequently, only one power supply is required. Thus, niobium-doped titania coatings were deposited on glass and Si wafer substrates by this hybrid HiPIMS-CVD technique. The TiO2 coatings were deposited by CVD from a titanium (IV) tetraisopropoxide precursor via the vapor drawn method. The HiPIMS process provided not only the source of the Nb metal dopant to the functional films but also sustained the low temperature CVD process by supplying energetic plasma particles. Furthermore, since HiPIMS deposition rates are very sensitive to magnetic field strength and the degree of unbalance, by using a magnetron with variable magnetic field strength, it was possible to adjust the dopant content of the film without adjusting the power applied to the magnetron target. The effect of processing parameters (pulse frequency, peak powers, precursor flow rates, operating pressure, etc.) on generating a stable HiPIMS discharge across the process envelope has been studied. The composition and microstructure of the deposited coatings have been investigated, in respect to variable process parameters, such as substrate temperature and operating pressure.