Study on Surface Modification of Indium Tin Oxide and Resist Surfaces Using CF4/O2 Plasma for Manufacturing Organic Light-Emitting Diodes by Inkjet Printing

We studied a surface modification technique for indium tin oxide (ITO) anodes without precleaning and resist banks for manufacturing organic light-emitting diodes (OLEDs) by inkjet printing. The ITO surface modified by inductively coupled plasma (ICP) with an optimized CF4/O2 (7:3) gas mixture improved both its hydrophilicity and its work function, while the resist surface treated by the plasma became hydrophobic. The resist and ITO surfaces treated by plasmas of various gas mixtures (i.e., CF4, CF4/Ar (1:2), CF4/O2 (x:1; x=1, 7/3, 4, and 9) were analyzed by X-ray photoelectron spectroscopy (XPS) of the C 1s, F 1s, O 1s, and In 3d5/2 core levels. On the uncleaned ITO surfaces modified by CF4/O2 plasmas, organic contaminants were removed more efficiently and the deposition of CFx on the remaining contaminants decreased with increasing oxygen. The amount of F in the form of InFx increased using the CF4/O2 (7:3) plasma in comparison with that using the CF4/Ar and CF4 plasmas. We investigated the effect of adding oxygen to CF4 on the change in gaseous species produced in the plasma chamber by mass spectrometry. In the CF4/O2 (7:3) plasma, the peak intensities of F+, HF+, F2+, O+, and O2+ were higher than those in the CF4 plasma. The results suggest that In2O3 was generated by the oxidation of indium with O, and InFx was generated by the fluoridation of indium with HF. By introducing InFx onto ITO surfaces using the CF4/O2 plasma, the hole-injection energy barrier could be reduced.