There will be more or less problems in the coating process of the pvd coating machine, such as uneven film layer, stains, defects, etc. This is the most troublesome thing for everyone, because after these adverse reactions occur, we have to rack our brains to investigate various It takes a lot of time and affects the progress of coating. Therefore, if we can try to avoid it in the early stage, we should try to avoid it. So when these adverse reactions occur, how should we deal with them? Let us introduce to you in detail how to deal with the adverse reactions of pvd coating machine coating?

First: When there is an adverse reaction in the coating of the pvd coating machine:
        1. Strengthen degreasing and decontamination treatment. If it is ultrasonic cleaning, it should focus on the degreasing function and ensure the effectiveness of the degreasing solution; if it is rubbed by hand, consider first wiping with calcium carbonate powder and then cleaning.
        2. Strengthen the pre-plating baking, if conditions permit, it is better that the substrate temperature can reach above 300 °C, and the constant temperature is more than 20 minutes, so that the water vapor and oil vapor on the surface of the substrate can be volatilized as much as possible. *Note: The higher the temperature, the greater the adsorption capacity of the substrate, and it is also easy to absorb dust. Therefore, the cleanliness of the vacuum chamber should be improved. Otherwise, there will be dust attached to the substrate before plating, which will affect the film strength in addition to other defects. (The chemical desorption temperature of water vapor on the substrate in vacuum is above 260°C). 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 greater relationship with stress and material thermal matching.
        3. When conditions permit, the unit is equipped with a condenser (PLOYCOLD), which not only increases the vacuum pumping speed of the unit, but also helps to remove water vapor and oil and gas from the substrate.
   4. Improve the vacuum degree of evaporation. For a pvd coating machine above 1 meter, the starting vacuum of evaporation should be higher than 3*10-3Pa. The larger the coating machine, the higher the starting vacuum of evaporation.
        5. When conditions permit, the unit installs an ion source, bombards it before plating, cleans the surface of the substrate, and assists in the coating process, which is conducive to the compactness and firmness of the film.
        6. To remove moisture from the membrane material, place the membrane material to be used in a petri dish in a vacuum chamber to dry.
        7. Keep the working environment dry (including lens wiping, umbrella work area), and do not bring in too much water vapor when cleaning the working environment.
        8. For multi-layer films, when designing the film system, it is necessary to consider the matching of the first layer of film and the substrate, and consider using Al2O3 film material as much as possible, which has good adsorption force to most of the substrates. For metal films, the first layer of Cr or Cr alloy can also be considered. Cr or Cr alloy also has better adsorption force to the substrate.
        9. Take the grinding liquid (polishing liquid) to re-remove the corrosion layer (hydrolysis layer) on the surface of the lens
       10. Sometimes appropriately reducing the evaporation rate is helpful to improve the strength of the film, and has positive significance for improving the smoothness of the film surface.

Second: pvd coating machine film stress:
         The film-forming process of the film is a transformation process of the material form. It is inevitable that there will be stress in the film layer after film-forming. For multi-layer films, there are combinations of different film materials. There are differences, some are tensile stress, some are compressive stress, and the existence of thermal stress of the film layer and the substrate is harmful to the film strength. cracked or reticulated slack. For the anti-reflection film, due to the small number of layers, the stress is generally not obvious (but some glass lenses have stress problems even with the anti-reflection film.) For high-reflection films and filter films with a large number of layers, the stress is A common adverse factor should be paid special attention.

Improve strategy:
        1. Bake after plating. After the last layer of film is plated, do not stop baking immediately, and continue to "temper" for 10 minutes. Make the film structure more stable.
        2. Properly extend the cooling time and anneal aging. Reduce thermal stress caused by excessive temperature difference between inside and outside the vacuum chamber.
        3. For high-reflection films, filter films, etc., during the evaporation process, the substrate temperature should not be too high, and high temperature is easy to generate thermal stress. And it has a negative effect on the optical stability of titanium oxide, tantalum oxide and other film materials. The coating process is ion-assisted to reduce stress.
        4. Select the appropriate film system matching, the matching of the first layer of film material and the substrate. (For example, the five-layer anti-reflection film adopts Al2O3-ZrO2-Al2O3-Al2O3-ZrO2-MgF2; ZrO2 can also use SV-5 (a ZrO2 TiO2 mixed film material) or other mixed high refractive index film material.
        5. Appropriately reduce the evaporation rate (Al2O3-2.5A/S; ZrO2-3A/S; MgF2-6A/S reference rate)
        6. All the oxide film materials are oxygenated for reaction plating, and the oxygen intake is controlled according to different film materials.
Third, the surface hardness of the outer film:
        The outer layer of the anti-reflection film is generally made of MgF2. The cross-section of the film layer is a relatively loose columnar structure, the surface hardness is not high, and it is easy to wipe out.
Improve strategy:
        1. When the film system design allows, add a SiO2 layer of about 10nm to the outer layer. The surface smoothness of silicon dioxide is worse than that of magnesium fluoride (but the surface wear resistance and hardness of silicon dioxide are not as good as magnesium fluoride). After plating, ion bombardment for a few minutes, the effect of firmness will be better. (but the surface will be rough)
        2. After the lens leaves the vacuum chamber, place it in a dry and clean place to prevent rapid moisture absorption and reduce surface hardness.

Fourth, other
       The reasons for the poor film strength are also that the vacuum is too low (it is easy to occur in manually controlled machines), the vacuum chamber is dirty, and the substrate heating is not in place. When the auxiliary gas is inflated, the film material is also deflated, which reduces the degree of vacuum, reduces the free path of molecules, and the film layer is not strong. Therefore, the filling of the auxiliary gas should consider the outgassing of the film material, and the film material should be fully pre-melted and fully outgassed before plating, and it can also avoid the excessive decrease of the vacuum degree caused by the outgassing of the film material during the evaporation, thus affecting the film strength.

Fifth, stripping
        Although the peeling here is also a weak film, it has some differences from the aforementioned peeling, and the main features are: point-like peeling, edge peeling, and local peeling. The main reason is that the membrane is dirty or polluted.
Improvement method: Improve the cleanliness of the substrate.
        The above five are the common adverse reaction problems of pvd coating machine coating, and the improvement methods. It is also a skill that a coating engineer must master. When these problems are encountered, they can be checked and solved in time.