Sputtering, usually refers to the magnetron sputtering, belongs to the sputtering method at low temperature. The process requirement of vacuum in 1 x 10-3 torr, namely 1.3 x 10-3 pa vacuum inert gas argon (Ar), and the plastic base material (anode) and metal target material (cathode) and high voltage direct current (dc), because the glow discharge (glow discharge) produced by the electronic excitation of inert gas, plasma, plasma to metal atom bomb out of target material, is deposited on the plastic base material
·Charged particles with dozens of electron volts or higher kinetic energy bombshell the material surface and splash it out into the gas phase for etching and coating. The number of atoms emitted by an ion is called sputtering Yield. The higher the Yield, the faster the sputtering rate will be. The highest rate is for Cu,Au,Ag, and the lowest is for Ti,Mo,Ta, and W. Generally in the 0.1-10 atom/ion.
·Ions can be generated by a direct current glow discharge. At a vacuum degree of 10-1-10 Pa, a high voltage is applied between the two electrodes to produce discharge.
·The current density in a normal glow discharge is related to the cathode material, shape and gas type pressure. Plating should be maintained as stable as possible.
·Any material can be sputtering coating, even high melting point materials are easy to sputtering, but for the non-conductor target must be RF (RF) or pulse (pulse) sputtering; And due to poor electrical conductivity, splashing power and speed is low. Metal splashing power up to 10W/cm2, non-metal < 5W/cm2
The target material is the cathode, the plated workpiece and the workpiece frame are the anode, and the higher plating rate can be obtained only when the pressure of gas (argon Ar) is about several Pa or higher
·An orthogonal electromagnetic field is formed on the surface of the cathode target, where the electron density is high and the ion density is improved, so that the sputtering rate is increased (by an order of magnitude), and the sputtering speed can reach 0.1 -- 1 um/min, and the film adhesion is better than that of steam plating. It is one of the most practical coating technologies at present.
·Other coating technologies include bias sputtering, reactive sputtering and ion beam sputtering
·Equipment and process of plating machine (magnetically controlled plating)
·The sputtering machine is composed of vacuum chamber, exhaust system, sputtering source and control system. The sputtering source is divided into power supply and sputter gun.
·Magnetron sputtering gun is divided into planar type and cylindrical type, among which planar type is divided into rectangular type and circular type, target material utilization rate is 30-40%, and cylindrical target material utilization rate is >50%
·Sputter power supply is divided into: DC, RF, pulse,
·Dc: 800-1000V (Max) conductor, can be disaster arc.
·Rf: 13.56MHZ, non-conductor.
·Pulse: widely used, the latest development
·Sputtering current, voltage or power, and sputtering pressure (5 10-1 -- 1.0Pa) should be controlled when sputtering. If all parameters are stable, the film thickness can be estimated.
·Target material selection and treatment is very important, purity to be good, uniform texture, no bubbles, defects, the surface should be smooth and smooth.
·For the direct cooling target, it should be noted that the target material becomes thinner after sputtering and may break, especially the non-metal target. In general, the thinnest part of the target shall not be less than half of the original target thickness or 5mm.
·The operation mode of magnetically controlled splash plating is similar to that of general steam plating. Firstly, vacuum is pumped to 1 10-2pa, and then argon (Ar) ions are injected to bombarding the target material. During the splash plating at the pressure of 5 10-1-1.0 Pa, attention should be paid to the current, voltage and pressure. At the beginning, if there is a spark in the splash plating, the voltage can be slowly raised, and shutter can be closed after the steady discharge.
In this process, the ionization of inert gas (Ar) cleaning and exposed the plastic base material on the surface of several small empty MAO, and through the electronic and the plastic substrate surface is clean and produce free radicals, and maintain the vacuum with coating and structure formation of a surface, the surface structure of the association and free radicals produce fill and high adhesion of the combination of chemical and physical state, form a thin film to outside surface firmly.
The film is first formed by filling the surface substrate roughly with the plastic hair pores and linking them. Compared with the common evaporation plating, splash plating has the advantages of strong adhesion between the coating and the substrate - the adhesion is more than 10 times higher than that of evaporation plating. Vacuum evaporation needs to vaporize the metal or metal oxide, and the heating temperature should not be too high, otherwise, the metal gas deposition in the plastic substrate heat and burn the plastic substrate. The sputtering particles are almost free from the influence of gravity, and the positions of the target and the substrate can be arranged freely. In the initial stage of film formation, the nucleation density is high, and the extremely thin continuous film below 10nm can be produced. The target material has a long life and can be automatically and continuously produced for a long time. Target materials can be made into various shapes, with the special design of the machine for better control and the most efficient production.
Splash plating USES high voltage electric field to produce plasma coating material, using almost all high melting point metals, alloys and metal oxides, such as: chromium, molybdenum, tungsten, titanium, silver, gold and so on. Moreover, it is a forced deposition process, using this process to obtain the coating and plastic substrate adhesion is much higher than the vacuum evaporation method. However, processing costs are relatively high.