The evaporation coating technology of pvd coating machine is the most conventional coating technology, which is characterized by simple equipment and easy operation. The film has high purity, good quality and controllable thickness. The speed is fast, the efficiency is high, the mask can be used to obtain clear patterns, and the film growth mechanism is relatively simple. Its disadvantage is that it is difficult to obtain a thin film with a crystalline structure, the adhesion between the thin film and the substrate is small, and the process repeatability is not good enough. Evaporation coating technology is the most conventional coating technology, and its daily application is very extensive. The demand for evaporation vacuum coating machines in the market is also very large. What is the operation principle of evaporation vacuum coating machines?

        Evaporating a substance by heating to deposit it on a solid surface is called evaporative coating. This method was first proposed by M. Faraday in 1857, and it has become one of the commonly used coating techniques in modern times. The operating principle of the evaporative pvd coating machine is to use the resistance heating method in the vacuum chamber to melt and vaporize the metal wire that is closely attached to the resistance wire, and the vaporized metal molecules are deposited on the substrate to obtain a smooth reflectivity film layer. The purpose of decorating and beautifying the surface of an item. The structure of the evaporation coating equipment is shown in Figure 1.
        Evaporation substances such as metals, compounds, etc. are placed in the crucible or hung on the hot wire as the evaporation source, and the workpiece to be plated, such as metal, ceramic, plastic and other substrates, is placed in front of the crucible. After the system is pumped to a high vacuum, the crucible is heated to evaporate its contents. The atoms or molecules of the evaporated substance are deposited on the surface of the substrate by condensation. The film thickness can vary from hundreds of angstroms to several microns. The film thickness is determined by the evaporation rate and time of the evaporation source (or by the amount of charge) and is related to the distance between the source and the substrate. For large-area coating, a rotating substrate or multiple evaporation sources are often used to ensure the uniformity of the film thickness. The distance from the evaporation source to the substrate should be less than the mean free path of the vapor molecules in the residual gas, so as to avoid chemical effects caused by the collision between the vapor molecules and the residual gas molecules. The average kinetic energy of vapor molecules is about 0.1 to 0.2 electron volts.
         There are three types of evaporation sources. ①Resistance heating source: use refractory metals such as tungsten and tantalum to make boat foil or filament, and pass electric current to heat the evaporation material above it or placed in the crucible. The resistance heating source is mainly used to evaporate Cd, Pb, Ag, Al, Cu, Cr, Au, Ni and other materials; ② high-frequency induction heating source: use high-frequency induction current to heat the crucible and evaporation material; ③ electron beam heating source: suitable for high evaporation temperature (not less than 2000 [ 618-1]), that is, bombarding the material with an electron beam to vaporize it.
       Compared with other vacuum coating methods, pvd coating machine evaporation coating has a higher deposition rate, and can coat elemental and compound films that are not easily thermally decomposed. In order to deposit high-purity single crystal films, molecular beam epitaxy can be used. The jet furnace is equipped with a molecular beam source. When it is heated to a certain temperature under ultra-high vacuum, the elements in the furnace are jetted to the substrate in a beam-like molecular stream. The substrate is heated to a certain temperature, the molecules deposited on the substrate can migrate, and the crystals grow according to the lattice order of the substrate. The molecular beam epitaxy method can obtain a high-purity compound single crystal film with the required stoichiometric ratio, and the film grows the slowest The speed can be controlled at 1 single layer/second. By controlling the baffles, single crystal thin films of desired composition and structure can be made precisely. Molecular beam epitaxy is widely used to fabricate various optical integrated devices and various superlattice thin films.