대면적 미세 Metal Mask 제작을 위한 전기화학식각 공정 개발

Abstract

Organic Light Emitting Diode (OLED) is solid state device composed of thin films of organic molecules. It emits light using electricity and does not require any backlight & color filter unlike Liquid Crystal Layer (LCD). Compared with LCD, OLED display is thinner and lighter because OLED display does not need backlight unit for emitting light. This display uses organic patterns to emit light. So, it is important to deposit organic patterns on the substrate. There are several methods to deposit organic compound patterns, such as Ink-jet method, Fine Metal Mask (FMM) method, and Laser Induced Thermal Image (LITI) method. Ink-jet method use ink-jet nozzle to inject organic compound on the substrate directly. But it is difficult to deposit organic patterns uniformly. FMM method use thin metal mask to deposit organic compound patterns. Organic compound patterns for RGB color are fabricated on substrate using an evaporator. So, to make organic pattern uniformly, it is important to fabricate FMM which has uniformed patterns. In the industry, there are several technologies to fabricate FMM, for example Laser machining, electroforming etc. Laser machining uses laser to make specific pattern on the substrate. This technology has some advantages. It can fabricate small patterns with fine pitch. Also, there is no limitation in substrate type. But, it is sequential process. If the number of mask patterns increases, process time and cost also increases. Electroforming process is not only costly but it is hard to control thickness uniformity as well. In this study, we introduced Through Mask Electrochemical Micromachining (TMEMM) process to fabricate FMM. TMEMM is one of the Electrochemical Machining (ECM) methods. ECM uses electrochemical reaction to removal materials. There are no mechanical and thermal stresses. But it is also sequential and localized removal process. So, if substrate is large, it needs to be machined simultaneously for better productivity. To satisfy this requirement, TMEMM is used. It involves selective metal dissolution form unprotected areas of dry-film resist (DFR) patterned workpiece. Various patterns in a large area can be etched at the same time. DFR patterned stainless steel substrate is used as anode and Cu plate used as cathode. DFR patterning process consists of substrate preparation, laminating, laser direct imaging and development step. Phosphoric acid (H3PO4, 86%) is used as electrolyte. And after TMEMM process, DFR is removed by dipping in 3M NaOH solution. In order to understand large area fabrication of FMM, I have implemented an experiment on smaller sample first. Through beaker scale test, we tried to understand influence of mass transport and current distribution. By controlling cathode size and stirring rate, we can understand mass transport. Also, by controlling exposed area of cathode, using insulation shield and dummy pattern, we can know current distribution is one of the key factors during TMEMM process. After TMEMM process, substrate is analyzed by optical microscope, 3D-profiler and Field-Emission Scanning Electron Microscopy (FE-SEM). Uniformity and etch rate is expressed by standard deviation (STD) and average hole diameter (Avg.dia.), respectively. With these results, we try to fabricate large area of FMM. As area of substrate became bigger, applied current and process time are increased, too. Consequently, we fabricated FMM successfully which has specific hole size: 245 µm average diameter and about 7 % standard deviation value. Through this study, we can know it is important to control current distribution and constant electrolyte flow and state of electrolyte (electric conductivity, pH).