Extraction of low‐energy negative oxygen ions for thin film formation

Coextraction of low‐energy positive and negative ions were performed using a plasma sputter‐type ion source system driven by a 13.56 MHz radio frequency (rf) power. Titanium (Ti) atoms were sputtered out from a target and the sputtered neutrals were postionized in oxygen/argon $(O2/Ar)$ plasma prior to extraction. The negative O ions were surface‐produced and self‐extracted. Mass spectral analyses of the extracted ion beams revealed the dependence of the ion current on the incident rf power, induced target bias and $O2/Ar$ partial pressure ratio. $Ti+$ current was found to be dependent on $Ar+$ current and reached a saturation value with increasing $O2$ partial pressure while the $O−$ current showed a peak current at around 1:9 $O2/Ar$ partial pressure ratio. $Ti+$ current was several orders of magnitude higher than that of the $O−$ current.