Paper PS-ThP10
The Role of Negative Oxygen Ions in the Pulsed-Plasma Deposition of Titania Films

Thursday, October 21, 2010, 6:00 pm, Room Southwest Exhibit Hall

Reactive pulsed magnetron sputtering is the process of choice to deposit commercially important oxide-based thin films and coatings. The technique relies on the plasma ions (e.g. Ar⁺, O⁺) assisting the deposition process through energetic impact at the substrate leading to good, dense coating structures.

However, in these systems copious amounts of negative ions (O^-, O₂^- O₃^-, MO_x^-) can be created at the cathode target. These ions are accelerated through the cathode sheath to bombard the substrate with upper energies equivalent to the target potential, (i.e. hundreds of eV). These ions easily overcome the negative substrate bias potentials, used to attract positive ions and can be wholly destructive to growth of engineering quality films.

In this study we use an eclipse laser photo-detachment technique combined with a Langmuir probe to measure the density of negative ions in the pulsed sputtering of titanium in oxygen-argon mixtures. This has been done at different positions in the plasma during different phases of the driving pulsed-voltage waveform. The results show that the total negative ion density can exceed that of the electrons and at positions close to the substrate on the discharge centre line, the fraction of very fast negative ions can be over 10% of the total observed. The power fluxes of these species at the substrate have been calculated and the effect on the growing TiO₂ film is discussed.