Vacuum Coating
One: The vacuum coating machine mainly refers to a type of coating that needs to be performed under a high degree of vacuum, including many types, including vacuum ion evaporation, magnetron sputtering, MBE molecular beam epitaxy, PLD laser sputtering deposition and many other types. The main idea is to divide into evaporation and sputtering.
Two: Vacuum coating machine has three pumps: mechanical pump (generally oil rotary pump), booster pump is also called roots pump
, High vacuum pump (diffusion pump or molecular pump)
Mechanical pump
It works from the atmosphere. The effect of mechanical pump exhaust is also related to the speed of the motor and the tightness of the belt. When the belt of the motor is relatively loose and the speed of the motor is very slow, the exhaust effect of the mechanical pump will become worse. Therefore, it is necessary to carry out regular maintenance and inspections. The sealing effect of the mechanical pump oil also needs to be inspected frequently. Too little oil will not achieve the sealing effect. There will be air leakage in the pump and too much oil. And exhaust, generally, 0.5 cm below the oil level can be.
Booster pump:
It is a mechanical pump with a pair of double-lobed or multi-lobed rotors that rotate synchronously and at high speed. Because it works the same as a Roots blower, it can also be called a Roots vacuum pump. This pump is in the pressure range of 100-1 Pa. It has a large pumping speed, which makes up for the shortcomings of insufficient exhaust capacity of the mechanical pump in this range. This pump cannot start from the atmosphere or directly exhaust the atmosphere. Its role is only to increase the air inlet and exhaust. The pressure difference between the ports, the rest requires a mechanical pump to complete, so it must be equipped with a mechanical pump as the foreline pump.
Oil diffusion pump: The ultimate vacuum of the mechanical pump is only 10-2 Pa. When it reaches 10-1 Pa, the actual pumping speed is only 1/10 of the theoretical. If you want to obtain high vacuum, you must use an oil diffusion pump.
Oil diffusion pump
The application pressure range is 10-1 Pa to 10-7 Pa. It uses the gas diffusion phenomenon to exhaust. It has the advantages of simple structure, convenient operation and large pumping speed (up to 10 + 5 liters / second). . The oil diffusion pump is mainly composed of a pump casing, a nozzle, a deflector and a heater, and a diffusion pump oil (Japanese model D-704 #) is mainly added therein, which can be divided into a single-stage pump and a multi-stage pump according to the number of nozzles.
When the oil of the diffusion pump is heated by the electric furnace, the generated oil vapor provides the front pressure, and the mechanical pump acts as the front pump. When the diffusion pump oil is heated by the electric furnace, the generated oil vapor is sprayed down through the umbrella nozzle along the guide pipe. Because there is a vacuum of 1-10-1 Pa provided by the mechanical pump outside the nozzle, the oil vapor can be sprayed for a distance, forming a jet moving in the direction of the air outlet. The jet finally hits the wall of the pump cooled by the cooling water, condenses into a liquid, and flows back to the evaporator, that is, the evaporation-jetting-condensation of the oil is repeated to realize the pumping.
