Structure modification of titanium oxide thin films by rf-plasma assistance in Ti-O2 reactive dc and pulsed dc sputtering

Titanium oxide films have been deposited by Ti-O-2 reactive direct current (dc) and pulsed dc sputtering under the presence of the secondary radio-frequency (rf)-plasma to the primary cathode discharge at various discharge pressures in order to reveal effects of rf-plasma assistance on film structure and properties. At low discharge pressures, film structure changes from anatase to rutile by rf-plasma assistance to dc and pulsed dc discharge. At high discharge pressures, films changes from the mixtures of weakly ordered anatase to amorphous by rf-assistance. Refractive index of films deposited increases by rf-plasma assistance in either of dc and pulsed dc sputtering, showing a highest index of 2.57 at a discharge pressure of 3.0 Pa. The enhancement of refractive index becomes remarkable at high discharge pressures. Furthermore, the surface of films becomes smoother by the presence of the secondary rf plasma. Being similar to the tendency of the refractive index change, the smoothening of film surface by the presence of the secondary rf plasma is remarkable at high discharge pressures. It is concluded that film structure changes from rutile to amorphous and is simultaneously densified by rf-plasma assistance to dc and pulsed dc discharge at a high discharge pressure, yielding films with a high refractive index and smooth surface. (c) 2012 Elsevier B.V. All rights reserved.