Deposition of Titanium Oxide Films by Current-Controlled High Power Impulse Magnetron Sputtering

TiOx films were produced in a cluster tool by reactive High Power Impulse Magnetron Sputtering (HIPIMS)of a pair of metallic targets in an Ar-Oxygen atmosphere.  The HIPIMS process was carried out by maintaining a constant current within the pulse.  This resulted in the elimination of stability issues associated with runaway currents and target poisoning for oxygen flows ranging from 10 to 50% of the total gas flow.  Time-resolved optical emission spectroscopy revealed that the plasma discharge developed through stages of gas ionisation, gas rarefaction and metal sputtering, the latter associated with cooling of the electron temperature.  Evidence is presented of metal ionisation and atomic oxygen sputtering from the target.  Films were deposited without intentional heating or substrate biasing and had good transparency.  The thickness uniformity was < 2% across a 100x100 mm area.  The refractive index increased continuously as the oxygen flow reduced from 45 to 13% reaching a maximum value of 2.55 at a wavelength of 550 nm.  The films were metallic (non-transparent) at 10% Oxygen flow.  The films comprised a mixture of rutile and anatase phase with HIPIMS deposition producing higher fractions of rutile compared to bipolar pulsed DC operation.   The HIPIMS films reached higher refractive index of 2.55 compared to 2.47 for bipolar pulsed DC.   The hardness of the films and its relation to process conditions are discussed.