Reduced Damage From Facing-Target Sputtering of Indium Tin Oxide Films

Abstract

This study addresses a current limitation in the development of high performance organic optoelectronic devices: depositing indium tin oxide (ITO), a transparent, conductive film, without damage to underlying organic films. ITO is deposited with a plasma sputter deposition process which causes damage to organic films. Previous research demonstrates that damage can be reduced with a sputtering configuration with substrates placed perpendicular to two facing guns. We employ fluorescent organic material Alq3 (tris-(8-hydroxyquinoline)aluminum) to explore damage caused by radio-frequency facing-target magnetron plasma sputtering by means of photoluminescence spectroscopy. We present an investigation of the degree to which Alq3 is damaged in the plasma sputtering process. We explore the dependence of the damage on the rate of growth. We evaluate the effects of closing the sputter system shutter to eliminate direct plasma exposure as well as the effect of employing a BPhen (bathophenanthroline) protective layer. We find that facing-target sputtering can be performed at a high growth rate without causing significantly more damage than that caused when sputtering is performed at a low growth rate, with only a 10% reduction in PL from a rate of 0.2 ̊A/s to 2.4 ̊A/s. We demonstrate that the greatest amount of damage occurs at the start of plasma sputtering. The BPhen protective layer is shown to mitigate damage to the surface of the organic material by exposure to gaseous ions.