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updated 05/02/2012

The Principle Of AR Coatings

Vacuum Deposition

Vacuum Evaporation is used to control making controller under vacuum.If the temperature raises enough, the material will get internal energy and be evaporated. The atoms of the evaporating material go right around the wall, and the atoms collide against the wall and become condensed and accumulated. This method includes the principle. The method of providing external energy as is needed for material evaporation is as follows: Filament, E-beam, Flash.

Thin Film Coating

Thin film coating skill is to control a complicated chemical reaction and to make it in a certain place as one of the ultra modem technologies.  It is important to manufacture high purity and high density materials.
A thin film with high added value needs vacuum technology for sintered thin film, auto parts, optical lenses, quality consumable goods. Thin film contributes to the innovation of the electronic industry.

In thin-film coating, a metal or compound is evaporated under high vacuum from a source onto a base material or substrate. The base material is generally plastic for decorative coatings; glass or plastic for optical coatings; and glass ceramic, or silica for electrical coatings. Thickness of the film can vary from about 1/4 wavelength of visible light to 0.001 inches or more. In the optical field, antireflection coatings are deposited on lenses for cameras, telescopes, eyeglasses, and other optical devices, considerably reducing the amount of light reflected by the lenses and thus giving a brighter transmitted image.

          To achieve vacuum high enough for thin-film coating and for other industrial uses requiring pressures down to 10^-6 torr, a pumping system consisting of an oil-sealed rotary pump and a diffusion pump is used. The oil-sealed rotary pump (sometimes referred to as forepump) "roughs" the chamber down to a pressure of about 0.1 torr, after which the roughing valve is closed. The fore valve and high-vacuum baffle valve are then opened so that the chamber is evacuated by the diffusion pump and rotary pump in series.

Vacuum Equipment

Oil-sealed Rotary Pump

          Capacities are available from 1/2 to 1,000 cubic feet per minute, operating from atmospheric pressure down to as low as 2 x 10^-2 torr for single-stage pumps and less than 5 x 10^-3 torr for two-stage pumps. The pumps develop their full speed in the range from atmosphere to about one torr. The speed then decreases to zero at their ultimate pressures. Two of the most common designs are useful for pumping both liquids and gases. One is a two-bladed pump in which the rotor is eccentric to the stator, forming a crescent-shaped volume swept by the blades through the outlet valve. The second, a rotary piston pump, similar to a single blade, is part of the sleeve fitting around the rotor. The blade is hollow and acts as an inlet valve, closing off the pump from the system when the rotor is at top center.

          Ultimate pressures attainable are limited by leakage between the high and low-pressure sides of the pump (due mainly to carry over of gases and vapors dissolved in the sealing oil that flash off when exposed to the low inlet pressure) and decomposition of the oil exposed to high temperature spots generated by friction.

          Gas ballasting helps to prolong pump life because it removes the chief source of pump contamination, condensable vapors. The gas ballast is a vented exhaust that admits a small amount of air at atmospheric pressure to the compression side of the pump, thus permitting most condensable vapors to pass through the pump without condensing.

          Typical applications of this pump are in food packaging, high-speed centrifuges, and ultraviolet spectrometers. It is also widely used as a fore pump or a roughing pump, or both, for most of the other pumps described.

Vapor Diffusion Pump

          This pump is mainly used on equipment for the study of clean surfaces and in radio frequency sputtering. Pumping speeds are available up to 190,000 cubic feet per minute with an operating pressure range of 10^-2 to less than 10^-9 torr when water-cooled baffles are used and less than 10^-11 torr when refrigerated baffles are employed. The pumping speed for a vapor pump remains constant from about 10^-3 torr to well below the ultimate pressure limitations of the pump fluid. The best fluids allow pressures of better than 10^-9 torr. The diffusion pump is initially evacuated by an oil-sealed rotary pump to a pressure of about 0.1 torr or less. When the pump fluid in the boiler is heated, it generates a boiler pressure of a few torr within the jet assembly. High-velocity vapor streams emerge from the jet assembly, impinge and condense on the water or air-cooled pump walls, and return to the boiler. In normal operation part of any gas arriving at the inlet jet is entrained, compressed, and transferred to the next stage. This process is repeated until the gas is removed by the mechanical fore pump.

          The oil-vapor booster pump works on the same principles as the diffusion pump, but it employs a higher boiler pressure. Normal operating pressure range is 1 to 10^-4 torr. When backed by an oil-sealed rotary pump, this pump is widely used for achieving high vacuum in thin-film evaporation units, accelerators, and in TV tube pumping.

Sputter Ion Pump

          Capacities are available up to 14,000 cubic feet per minute, with an operating pressure range of 10^-11 torr. The full speed of the pump is developed in the pressure range from about 10^-6 to 10^-8 torr, although the characteristic at the lower pressure is dependent on the pump design. This pump uses a cathode material such as titanium vaporized or sputtered by bombardment with high velocity ions. The active gasses are pumped by chemical combination with the sputtered titanium, the inert gasses by ionization and burial in the cathode, and the light gasses by diffusion into the cathode.

          A typical pump consists of two flat rectangular cathodes with a stainless steel anode between them made up of many open-ended boxes. This assembly, mounted inside a narrow box attached to the vacuum system, is surrounded by a permanent magnet. The anode is operated at a potential of about seven kilovolts (kV), whereas the cathodes are at ground potential.

          The sputter ion pump has low speeds and sometimes instability when pumping inert gases. To improve its characteristics other types of sputter ion pumps have been developed: the slotted cathode, triode, differential, and magnetron pumps.

          To start up a sputter ion pump it is necessary to reduce the pressure to at least 2 x 10^-2 torr, and preferably much lower, by means of a roughing pump. Sputter ion pumps can operate in any position and do not need water or liquid nitrogen supplies. They have a long life and can provide very clean, ultrahigh vacuum, free of organic contamination and vibration. They are employed mainly for the clean-surface studies and in those applications where any organic contamination will give unsatisfactory results.

      Sputtering Target                                                          SIO2