How to improve the problems of vacuum coating equipment
In the process of vacuum coating, if your vacuum coating machine has problems, you can refer to the following methods to improve:
(1) Strengthen the degreasing and decontamination treatment. If it is ultrasonic cleaning, the degreasing function should be focused on, and the effectiveness of the degreasing solution should be ensured; if it is hand-wiping, consider first wiping with calcium carbonate powder and then wiping.
(2) Strengthen the baking before plating. If the conditions permit, the substrate temperature can reach 300℃ or higher, and the constant temperature should be more than 20 minutes, so as to make the water vapor and oil vapor on the surface of the substrate volatilize as much as possible. *Note: The higher the temperature, the greater the adsorption capacity of the substrate, it is also easy to adsorb dust. Therefore, the cleanliness of the vacuum chamber should be improved. Otherwise, dust will adhere to the substrate before plating, which will affect the strength of the film in addition to other defects. (The chemical desorption temperature of water vapor on the substrate in vacuum is above 260℃). But not all parts need to be baked at high temperature, some nitrate materials have high temperature, but the film strength is not high, and stains will occur. This has a greater relationship with stress and thermal matching of materials.
(3) When conditions permit, the unit is equipped with a condenser (PLOYCOLD), which can not only increase the vacuum pumping speed of the unit, but also help the substrate to remove water vapor and oil and gas.
(Iv) Increase the vacuum degree of evaporation. For coating machines 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 possible, the unit installs ion source, bombards before plating, cleans the surface of the substrate, and assists the plating process, which is conducive to the compactness and firmness of the film.
(Vi) To remove moisture from the membrane material, place the membrane material to be used in a petri dish in a vacuum chamber for drying.
(Vii) Keep the working environment dry (including lens wiping, umbrella working area), and do not bring in too much water vapor when cleaning the working environment.
(Viii) For multi-layer films, when designing the film system, it is necessary to consider the matching of the first film and the substrate, and consider using Al2O3 film material as much as possible. This film material has good adsorption power for most of the substrates. For metal films, the first layer of Cr or Cr alloy plating can also be considered. Cr or Cr alloys also have better adsorption power to the substrate.
(Ix) Adopt polishing liquid (polishing liquid) to regenerate and remove the corroded layer (hydrolyzed layer) on the surface of the lens
(X) Sometimes a proper reduction of the evaporation rate is helpful to increase the strength of the film, and it is of positive significance to improve the smoothness of the film surface.
The film formation process of a thin film is a transformation process of material form. It is inevitable that there will be stress in the film layer after film formation. For multilayer films, there are combinations of different film materials, and the stresses reflected by each film layer There are differences, some are tensile stress, some are compressive stress, and there are thermal stresses of the film and the substrate.
The existence of stress is harmful to the strength of the film. The lighter one means that the film cannot withstand friction, and the heavy one causes cracks or thin nets in the film.
For anti-reflection films, the stress is generally not obvious due to the small number of layers. (However, some nitrate lenses have stress problems even if they are anti-reflection films.) For high-reflection films and filter films with more layers, the stress is A common undesirable factor should be paid special attention to.
(1) Bake after plating. After the last layer of film is plated, do not stop the baking immediately, continue "tempering" for 10 minutes. Let the film structure stabilize.
(2) The cooling time is appropriately extended, and the annealing time is effective. Reduce the thermal stress caused by the excessive temperature difference between the inside and outside of the vacuum chamber.
(3) In the evaporation process of high reflection film, filter film, etc., the substrate temperature should not be too high, as high temperature is likely to cause thermal stress. And it has a negative effect on the optical stability of titanium oxide, tantalum oxide and other film materials.
(3) Ion assist in the coating process to reduce stress.
(Iv) Choose the appropriate film system to match, the first layer of film material and the substrate match. (For example, the five-layer anti-reflection film uses 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 materials.
(5) Appropriately reduce the evaporation rate (Al2O3-2.5A/S; ZrO2-3A/S; MgF2-6A/S reference rate)
(Vi) Oxygenation and reaction plating of all oxide film materials, and control the oxygen gas intake according to different film materials.
③ Surface hardness of outer film:
The anti-reflection film generally uses MgF2 as the outer layer. The section of the film is a loose columnar structure, and the surface hardness is not high, so it is easy to wipe the road.
(1) When the film system design permits, add a 10nm SiO2 layer 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 a few minutes of ion bombardment after plating, the effect of firmness will be better. (But the surface will become thicker)
(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.
The reasons for the poor film strength include low vacuum (prone to occur in manually controlled machines), dirty vacuum chamber, and insufficient substrate heating.
When the auxiliary gas is filled in, the membrane material is also outgassing, which reduces the vacuum degree, reduces the molecular free path, and the membrane layer is not strong. Therefore, when the auxiliary gas is filled, the degassing of the film material should be considered. The film material is fully pre-melted and fully degassed before plating, which can also avoid the excessive decrease of the vacuum degree due to the degassing of the film material during evaporation, which affects the film strength.
⑤ Take off the film
Although the film release here is also a kind of weak film, it has some differences from the previous film release. The main features are: point release, edge release, and partial release.
The main reason is that there are dirt or pollutants in the membrane.
Improvement method: improve the cleanliness of the substrate.
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