Influence of energetic bombardment on stress, resistivity, and microstructure of indium tin oxide films grown by radio frequency magnetron sputtering on flexible polyester substrates

Using rf magnetron sputtering, we have identified conditions for growing indium tin oxide (ITO) thin films at room temperature that simultaneously exhibit low resistivity (∼3x10-4 Ω cm), high optical transparency (>80%), and near-zero stress on polyester substrates. From transport measurements, we deduced that Sn donor atoms had little effect on electrical conduction in ITO films. We further concluded from an analysis of sputtered ions and atoms that bombardment by energetic (>35 eV) negative oxygen ions caused high stress (∼1 GPa) in films grown at lower (6 mTorr) pressure. We further concluded that bombardment by lower-energy (1-2 eV) sputtered oxygen species at the growing film surface was likely responsible for the dependence of ITO crystallization and microstructure on oxygen partial pressure during deposition