Many coating engineers have often experienced this situation. Obviously, in the coating process of the pvd coating machine, the links are well controlled, but it is inevitable that inferior coating products will be produced. I don't know how to deal with it, because during the coating process, occasionally there is a bad coating, which is inevitable. The following Xiaobian will introduce to you how to improve the countermeasures for common defective coating products and reduce the probability of defective products.

A common problem that many people often encounter is the problem of film strength. In fact, film strength is an important indicator of lens coating, and it is also the most common defect in the coating process. Poor film strength (weak film) is mainly manifested as: wiping or tearing with special tape, resulting in sheet shedding; wiping or tearing with special tape, resulting in spot-like shedding; after boiling for 15 minutes, tearing with special tape produces spots The shape or sheet fell off; rubbed with a special rubber head and a force of 1Kg for 40 times, and there were traces; when the film was wiped or not wiped, cracks and meshes appeared.
       Then the film hardness encounters these problems, how to deal with it, ① the combination of the substrate and the film. In general, in anti-reflection films, this is the main reason for the weakness of the film. Since the surface of the substrate will inevitably have some harmful impurities attached to the surface during the optical cold working and cleaning process, and the surface of the substrate will always have some damage layers due to the effect of optical cold working, and impurities (such as water vapor) that penetrate into the damage layer , oil vapor, cleaning liquid, wiping liquid, polishing powder, etc., of which water vapor is the main one), it is difficult to remove it by ordinary methods, especially for substrates with good hydrophilicity and strong adsorption. When the film material molecules accumulate on these impurities, it affects the adhesion of the film layer, which also affects the film strength. In addition, if the hydrophilicity of the substrate is poor and the adsorption force is poor, the adsorption to the film layer is also poor, which will also affect the film strength. The chemical stability of the nitrate material is poor, and the surface of the substrate has been corroded during the circulation process in the pre-processing process, forming a corrosion layer or a hydrolysis layer (perhaps localized and extremely thin). When the film is plated on the corrosion layer or the hydrolysis layer, its adsorption is poor, and the film firmness is poor. The surface of the substrate has dirt, oil spots, gray spots, drool spots, etc., and the local film layer is poorly adhered, resulting in poor local film firmness.
 
Since there will be various situations in the hardness of the film layer, there will naturally be various improvement measures:
       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 to be wiped by hand, consider first wiping with calcium carbonate powder and then wiping.
       2. Strengthen the pre-plating baking, if conditions permit, it is better that the substrate temperature can reach above 300 ℃, 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.
      Fourth, improve the vacuum degree of evaporation. For the pvd coating machine above 1 meter, the vacuum at the start of evaporation should be higher than 3*10-3Pa. The larger the coating machine, the higher the vacuum at the start of evaporation.
      5. When conditions permit, the unit should install an ion source, bombard it before plating, clean the surface of the substrate, and assist in the coating process, which is conducive to the compactness and firmness of the film.
      6. Dehumidification of the film material, put the film 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 abrasive 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.