OLED(Organic Light Emitting Diode) 제조공정에서 미세입자 제거를 위한 세정 공정 최적화 연구

Abstract

Recently, panel size has become increasingly large reaching the 8th generation (2200mm × 2500mm) and there is a trend that is changing from a-Si TFT (amorphous-Si Thin Film Transistor) to oxide TFT because of a demand for high resolution display and an expansion of OLED (Organic Light Emitting Diodes) industry. In previous panel manufacturing processes, cleaning process was not so important. However, nowadays pixel size is becoming smaller and the number of pixels per unit area is gradually increasing due to the high resolution. Consequently, an influence of submicron sized contaminated particles is increasing, so the importance of cleaning process has increased. In the oxide TFT, to achieve the high resolution, Cu based gate structure having a low resistance characteristic is necessary and in order to prevent a leakage current through the active layer, SiO2 deposition is needed on a gate insulator layer and ITO (Indium Tin Oxide) layer is used as a transparent electrode. Also, the active layer needed to change from amorphous Si (a-Si) to IGZO (Indium Gallium Zinc Oxide) as the electron mobility of IGZO is faster than that of a-Si. For a large area and high resolution panel with a good production yield, a research on an effective cleaning process which can remove the submicron contaminated particles deposited on the IGZO, Cu, SiO2, ITO and IGZO substrate surfaces during a TFT manufacturing process is required. Generally, physical cleaning processes are used to remove the submicron particles in FPD (Flat Panel Display) process. Among them, a research on an eco-friendly physical cleaning processes such as DI water megasonic, H2-DIW functional water, mixing-jet, PVA brush, electrolyzed ionized water (EIW) and steam is actively being carried out. In this study, we have optimized these cleaning processes to remove the submicron particles from the substrate surface. The primary objective is to establish an optimal cleaning process by applying above processes for the Cu, SiO2, ITO and IGZO substrates. And a mechanism of cleaning process and a theoretical understanding of interaction force such as van der Waals force, zeta potential and electrostatic force between the particle and substrate for the optimization of particle cleaning are studied. In the course of the experiment, the particles (glass and aluminum) which were produced in TFT manufacturing process were intentionally deposited on the Cu, SiO2, ITO and IGZO substrate surfaces. And then, the cleaning test using megasonic (1 MHz and 250 W), H2-DIW functional water (0.1 MPa H2 gas pressure), mixing-jet (570 lpm CDA and 4 lpm DI water), brush (diamond shape), EIW (pH 10.2 and -790 mV ORP) and Steam (1300 lpm CDA and 5 lpm DI water) processes was conducted. We used single cleaning process and combination of cleaning processes to optimize the particle removal efficiency on each substrate. After that, we evaluated the cleaning efficiency by counting the number of particles on the surface before and after the cleaning test using an optical microscope. And also, we evaluated the surface roughness after the cleaning test by using atomic force microscope (AFM). As a result, we achieved a high cleaning efficiency of above 95% on each substrate. We found that the optimized combinations of cleaning process on each substrate, Cu (PVA brush cleaning → DIW applying megasonic cleaning), SiO2 (EIW applying megasonic cleaning), ITO and IGZO (EIW applying megasonic cleaning → steam cleaning).