Causes of poor optical film strength:

Bonding of substrate and film layer. In general, in the antireflection film, this is the main reason for the weak film. During the optical cold processing and cleaning process, some harmful impurities will inevitably adhere to the surface of the substrate. However, due to the effect of optical cold processing, there are always some damaged layers on the surface of the substrate, and the impurities (such as water vapor, oil vapor, cleaning liquid, wiping liquid, polishing powder, etc.) that penetrate into the damaged layer are difficult to remove by general methods, especially for the substrate with good hydrophilicity, This is especially true for substrates with strong adsorption. When the film material molecules are stacked on these impurities, the adhesion of the film layer is affected, which also affects the film strength. In addition, if the hydrophilicity of the substrate is poor and the adsorption force is poor, the adsorption on the film layer is also poor, which will also affect the film strength. The chemical stability of the nitrate material is poor. During the circulation of the substrate during the pre-processing process, the surface has been corroded, forming a corrosion layer or hydrolysis layer (maybe local and extremely thin). If the film layer is plated on the corrosion layer or hydrolysis layer, its adsorption is poor and the film firmness is poor. There are dirt, oil spots, gray spots, saliva spots, etc. on the surface of the substrate, and the adhesion of local film layer is poor, resulting in poor local film firmness.

Improvement measures:

First, strengthen the degreasing and decontamination treatment. In case of ultrasonic cleaning, the degreasing function shall be mainly considered and the effectiveness of the degreasing solution shall be ensured; In case of hand wiping, consider wiping with calcium carbonate powder before cleaning.

(II) strengthen baking before plating. If conditions permit, it is better that the substrate temperature can reach more than 300 ℃ and keep constant temperature for more than 20 minutes to volatilize the water vapor and oil vapor on the substrate surface as much as possible* Note: the higher the temperature, the greater the adsorption capacity of the substrate, and the easier to absorb dust. Therefore, the cleanliness of the vacuum chamber should be improved. Otherwise, dust will adhere to the substrate before plating, which will not only cause other defects, but also affect the film strength. (the chemical desorption temperature of water vapor on the substrate in vacuum is above 260 ℃). However, not all parts need to be baked at high temperature. Some nitrate materials have high temperature, but the film strength is not high, and there will be color spots. This has a great relationship with the stress and the thermal matching of the material.

Third, when conditions permit, the unit is equipped with a condenser (ploycold), which can not only improve the vacuum pumping speed of the unit, but also help remove water vapor and oil gas from the substrate.

(IV) improve the vacuum degree of evaporation. For the coater over 1m, the startup vacuum of evaporation shall be higher than 3 * 10-3pa. The larger the coater, the higher the startup vacuum of evaporation.

(V) when conditions permit, the unit shall install ion source, bombard before plating, clean the substrate surface, and assist the coating process, which is conducive to the compaction and firmness of the film layer.

(VI) dehumidification of membrane materials: put the membrane materials to be used in a Petri dish in a vacuum chamber for drying.

VII. Keep the working environment dry (including lens wiping and umbrella working area), and do not bring too much water vapor when cleaning the working environment.