Submicron Particle Removal during FPD Oxide TFT Process

Recently, panel size has become increasingly large reaching the 8^th 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. 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 Cu, SiO₂and ITO 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, mixing-jet, brush and electrolyzed ionized water (EIW) 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 and ITO 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 and ITO substrate surface. And then, the cleaning test using megasonic (1 MHz and 250 W), mixing-jet (570 lpm CDA and 4 lpm DI water), brush (diamond shape) and EIW (pH 10.2 and -790 mV ORP) processes was conducted. 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. As a result, we achieved a high cleaning efficiency of above 95% in the electrolyzed ionized water cleaning process by applying the megasonic cleaning on all substrates.