Strictly deal with the vacuum coating problem of PVD Vacuum coating machine
Some more detail need consider is that there has dust on the surface of the coating material, the equipment must be cleaned and maintained after the vacuum coating machine has been used for a period of time. In addition, it is very important to standardize the operation personnel and operation requirements, including wearing professional clothing, gloves, foot covers, etc. The substrate material should be treated strictly to make it clean and meet the process requirements. The target or the coating material must meets the necessary purity. Ensure that the facilities, equipment and operating environment are clean, dry. Reduce the indoor air flow of vacuum coating equipment, minimize the invasion of outdoor dust and so on to make sure the environmental temperature and humidity meets the normal standard demand.
The PVD vacuum coating process is very complicated. Due to the different coating principles, it can be divided into many types. It has a unified name only because it requires a high vacuum. Therefore, the factors affecting the uniformity of PVD vacuum coating with different principles are different. The concept of uniformity itself will have different meanings depending on the scale of the coating and the composition of the film.
Film uniformity concept:
1. The uniformity of thickness can also be understood as roughness. In terms of the scale of the optical film (that is, 1/10 wavelength as a unit, about 100a), the uniformity of the vacuum coating is quite good, so the roughness can be easily controlled within 1/10 of the visible light wavelength, which means that the film There is no obstacle to the optical characteristics.
But if the uniformity of the atomic layer scale, that is, the surface flatness of 10A or even 1a, is the main technical content and technical bottleneck of vacuum coating. The specific control factors will be explained in detail according to different coating factors.
2. Uniformity of chemical composition:
In other words, in the film, the atomic group of the compound tends to have uneven characteristics due to its small size. If the coating process of sito3 film is unscientific, the actual surface composition is not sito3, but may be other proportions. The chemical composition of the coating is not the required film, which is also the technical content of vacuum coating.
3. Uniformity of grid order:
This determines that the film is monocrystalline, polycrystalline, or amorphous, which is a hot issue in vacuum coating technology. See below for details.
There are two main categories:
There are many types of evaporative deposition coatings and sputtering deposition coatings, including vacuum ion evaporation, magnetron sputtering, molecular beam epitaxy, sol-gel method and so on.
1. For evaporative coating:
In general, after the target is heated, the surface components are evaporated in the form of atomic clusters or ions and deposited on the surface of the substrate to form a thin film through the film formation process (scattering island structure-stray structure-layered growth).
The thickness uniformity depends on:
1. The lattice matching degree of the substrate material and the target material
2. Substrate surface temperature
3. Evaporation power and rate
5. Coating time and thickness.
The uniformity of the evaporative coating composition is not easy to guarantee, and the specific factors can be as specified above. However, due to the limitation of the principle, for non-single-component coatings, the uniformity of the evaporation coating components is not good.
Uniformity of crystal orientation:
1. Lattice matching
2. Substrate temperature
3. Evaporation rate
2. For sputtering coating, it can be simply understood that the target is bombarded by electrons or high-energy lasers, and the surface components are sputtered out in the form of atomic clusters or ions, and finally deposited on the surface of the substrate, and then a thin film is formed through the film forming process.
Sputter coating can be divided into many types. Generally speaking, the difference with evaporation coating is that the sputtering rate will become one of the main parameters.
The uniformity of the PLD element is easy to maintain, while the atomic-scale thickness uniformity is relatively poor (due to pulse sputtering), and the control of the crystal growth direction (outer edge) is relatively general. With PLD
For example, the influencing factors are: the matching degree of the target material and the substrate lattice, the coating atmosphere (low-pressure gas atmosphere), the substrate temperature, the laser power, the pulse frequency and the sputtering time. For different sputtering materials and substrates.
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