Photoresist, also known as photochemical etching agent, refers to materials that undergo changes in solubility when exposed to ultraviolet light, electron beams, ion beams, X-rays, etc. It is the core material of the photolithography process, mainly composed of resin, photosensitizer, solvent, and additives, among which resin and photosensitizer are the most critical components.
Depending on the application field, photoresists can be divided into semiconductor photoresists, LCD photoresists, and PCB photoresists. In the field of LCD displays, the photoresists used for making color filters mainly include black photoresist, color photoresists (R,G,B), and transparent photoresist.
1. Color Filter Process
The color filter (Color Filter, CF) is a key component for colorizing LCD displays, serving to achieve color display on the LCD panel. There are various methods for producing color filters, including dyeing method, dye dispersion method, electrophoretic method, printing method, and inkjet method. Among these, the pigment dispersion method has advantages in color characteristics, quality, and reproducibility, making it the mainstream method for producing color filters.
The pigment dispersion method is a process that evenly disperses pigments in an appropriate medium to form a uniform pigment suspension, which is then coated onto the substrate material. The main process flow includes coating, pre-baking, exposure, developing, and post-baking.
2. Components of Color Photoresist
Photoresist mainly consists of solvent, resin, photosensitizer, and additives, with the solvent accounting for about 50%~90%, resin about 10%~40%, photosensitizer about 1%~6%, and additives less than 1%. The color photoresist mainly adds pigment (5%~10%) and dispersant (5%~10%) on this basis, where the pigment is used for coloring the photoresist, and the dispersant is used to evenly disperse the pigment.
Due to the presence of pigments in color photoresists, the technical requirements are higher compared to pigment-free photoresist systems. It requires effective pigment dispersion stability technology, and since pigments have opacity, it needs to have a high-sensitivity photoresist system. The performance of high-sensitivity photoinitiators and resins plays a decisive role in color photoresists.
3. Preparation of Color Photoresist
The production process of color photoresist includes steps such as raw material preparation, mixing, dispersion, filtration, and packaging. First, prepare the raw materials according to the formula, then add the raw materials into the reaction kettle for mixing until uniform, filter out large particles from the photoresist through a filter, and finally package and store it in barrels.
4. Development of Color Photoresist
As end-user products continue to pursue lighter, thinner, and high-quality displays, LCD panels are gradually developing towards high brightness, high contrast, high color saturation, and high resolution. In line with the needs of LCD panels, the development of color photoresists must also advance towards high transmittance, high color saturation, and high resolution.
1. To meet the high brightness requirements of LCD panels, it is necessary to develop color photoresists with high transmittance.
2. High color saturation requires the development of color photoresists with high color saturation (NTSC).
3. High resolution requires color photoresists to have the ability to produce finer lines.