In addition to the main materials, auxiliary materials are also needed to make LCDs. Auxiliary materials refer to raw materials used in the production process but not in the final product, mainly including photoresist and its diluent, P diluent, NMP, BC liquid, SiO2 diluent, rubbing cloth, isopropyl alcohol, ethanol, acetone, cleaning agent, acid, alkali, etc.

Photoresist

Photoresist, also known as photosensitive glue, is generally composed of photosensitizer (photoresist), sensitizer and solvent. Photosensitizer is a particularly sensitive polymer compound. When it is irradiated with light of appropriate wavelength, it can absorb a certain amount of light energy, causing it to undergo photochemical reactions such as cross-linking polymerization or decomposition, causing the photoresist to change its properties.

1) Classification of photoresists

Photoresist is the main material for photolithography. There are many types of photoresists. At present, there are more than 40 types of photoresists at home and abroad. According to the changes in the solubility characteristics of photoresists before and after exposure, photoresists can be divided into two categories: positive glue and negative glue.

Negative glue is soluble in certain organic solvents (such as acetone, butanone, cyclohexanone, etc.) before exposure, and undergoes photopolymerization after exposure, and is insoluble in organic solvents. When it is used for photolithography, a pattern completely opposite to the light-shielding pattern of the photolithography mask will be obtained on the substrate surface, so it is called negative glue.

Positive glue is insoluble in certain solvents before exposure, but becomes soluble after exposure. When using this type of photoresist for photolithography, you can get the same pattern as the light-shielding pattern of the photolithography mask, so it is called positive photoresist.

The schematic diagram of the pattern change of positive photoresist and negative photoresist after illumination is shown in Figure 1:

（Figure 1）

2) Main technical indicators of photoresist The performance of photoresist has a great influence on the quality of photolithography. It is customary to use indicators such as sensitivity, resolution, corrosion resistance, adhesion and pinhole density to measure its quality.

(1) Sensitivity:

Sensitivity is a performance indicator that characterizes the sensitivity of photoresist to light. Different sensitivities indicate different sensitivity to light, that is, different exposure amounts required for photochemical reactions.

For an exposure machine with a fixed light intensity, the higher the sensitivity of the photoresist, the shorter the exposure time; conversely, the exposure time needs to be correspondingly longer.

(2) Resolution:

Resolution is one of the indicators that characterize the photolithography accuracy of photoresist. It is not only related to the photoresist itself, but also to the photolithography process conditions and operating technical factors.

(3) Corrosion resistance:

It is usually required that photoresist has good corrosion resistance to acid and alkali chemical etching solutions, that is, it can withstand the immersion of acid and alkali etching solutions for a long time. In fact, photoresist can only have good corrosion resistance when the pinhole density is small and the adhesion performance is good.

(4) Adhesion ability: Adhesion ability refers to the degree of adhesion between the photoresist and the substrate, which directly affects the accuracy after photolithography. The adhesion of photoresist is not only related to the properties of the photoresist itself, but also closely related to the properties of the substrate and its surface conditions. A flat, dense, clean and dry substrate surface is conducive to the adhesion of photoresist. In addition, factors such as the ratio of photoresist, pre-baking conditions and developer formula will also affect the adhesion of photoresist.

(5) Stability:

In production, photoresist is required to have a certain stability, that is, the photoresist should not undergo dark reaction under normal temperature and light (mainly ultraviolet light) shielding. The photoresist is required to have a low impurity content and no residue after development.

(6) Pinhole density: The number of pinholes per unit area of the photoresist film is called the pinhole density of the photoresist film. The pinhole density of the photoresist film is required to be as low as possible.

(7) Viscosity and solid content: The viscosity and solid content of photoresist are the main factors affecting the thickness of the coating film. The thicker the photoresist, the greater its viscosity (i.e., the thicker it is). Under the same coating conditions, the thicker the resulting film is; conversely, the viscosity is small and the film is thin. Therefore, the viscosity of the glue can be adjusted by changing the concentration of the glue solution, thereby controlling the thickness of the glue film.

Other auxiliary materials

Other auxiliary materials include liquid materials such as concentrated hydrochloric acid, concentrated nitric acid, sodium hydroxide, cleaning solution, ethanol, acetone, various screens, and other auxiliary tools. These materials also play a very important role in the production process of liquid crystal displays. The functions of these auxiliary materials are as follows:

(1) Concentrated hydrochloric acid and concentrated nitric acid are used to corrode TTO films that are not covered by photoresist.

(2) Sodium hydroxide is used to clean ITO glass and remove impurities on the glass surface; it is used as a developer during photolithography to dissolve the photoresist in the unexposed part; it is used for stripping after photolithography to remove the photoresist on the corroded glass surface.

(3) Cleaning fluid is used to remove organic impurities on the glass surface and between two pieces of glass, including isopropyl alcohol and other types of cleaning fluid.

(4) Ethanol and acetone are mainly used to wipe impurities on the surface of the LCD screen and clean containers.

(5) Film plate is a black and white pattern corresponding to the electrode pattern on the film through the platemaking method. When exposed, the transparent area photoresist reacts under the action of light.

(6) APR plate is used for selective coating of orientation layer (PI and Si0,).

(7) Silk screen is used to screen print box, and the sealing glue and conductive glue are omitted.

(8) Friction cloth is used to align the liquid crystal molecules, that is, through the orientation friction between the friction cloth fluff and the glass surface, many grooves are generated on the glass surface.

(9) Cutting wheel is used on precision cutting machine. The material is diamond abrasive and is used to make knife marks on the glass surface.

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