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vacuum coating machine detailed structure

High vacuum coating machine, coating machine is the most widely used equipment for vacuum conditions. Its related components and components: mechanical pump, booster pump, oil diffusion pump, condensing pump, vacuum measurement system.


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vacuum main body -- vacuum chamber

In accordance with the requirements of processing product of each different, the size of the vacuum chamber is different also, the most used has a diameter of 1.3 M, 0.9 M, 1.5 M, 1.5 M, such as cavity is made by stainless steel material, asked not to rust, solid, etc., vacuum chamber have connection valve parts, used to connect the pump pu.

Auxiliary pumping system

The exhaust system is composed of "diffusion pump + mechanical pump + roots pump + cold trap +polycold".

Exhaust process is: the mechanical pump vacuum cavity first to less than 2.0 * 10-2 pa state of low vacuum, provides the prerequisite for the subsequent diffusion pump vacuum, when the diffusion pump vacuum cavity, after mechanical pump with series of oil diffusion pump, complete extraction action in such a way.

The exhaust system is an important part of the vacuum system of the coating machine, which mainly consists of mechanical pump, booster pump (mainly introduced roots pump) and oil diffusion pump.

Mechanical pump: also called backing pump, mechanical pump is the most widely used a low vacuum pump, it is to keep oil sealing effect and mechanical method of changing inside the pump suction cavity volume, cause the container inside the volume of a gas expanding vacuum is achieved.

Mechanical pump has a lot of kinds, common has slide valve type (this is mainly used in large equipment), the piston reciprocating, chip and chip (the most widely used at present, this paper mainly introduces) four types.

Mechanical pump is often used to, but the dry air, but not containing too much oxygen, explosive and corrosive gas, mechanical pump is generally used to smoke in addition to the permanent gases, but no good result to moisture, so it can't pumping water. Rotary vane pump parts plays the leading role is in the stator, rotor, shrapnel, etc., the stator but in stator and rotor different spindle, like two inscribed circle, rotor slot is equipped with two pieces of shrapnel, between the shrapnel equipped with spring, guarantee the shrapnel tightly posted on the interior surface of the stator.

Its two pieces of shrapnel alternate in two ways, from the air intake to the gas, on the other hand, to compress the gas that has been sucked in, and to pump the gas out of the pump. Each rotation of the rotor, the pump completes two inspirations and two exhaust. When the pump is continuously rotating clockwise, the rotary vane pump continuously inhales the gas through the intake port, and from the exhaust outlet continuously discharging the pump, to realize the purpose of pumping gas to the container. In order to improve the limiting vacuum pump, the pump stator soaked in oil, and everywhere in the clearance of harmful space often keep sufficient oil inside, fill the gap, so the oil lubrication, on one hand, on the other hand and seal and plug gap and the harmful effect of the space, prevent gas molecule reverse flow through various channels to the low pressure of space.

The mechanical pump starts from the atmosphere, and its main parameters are the limit vacuum and the pumping rate, which is an important basis for the design and selection of mechanical pumps. The single-stage pump can pump the container from the atmosphere to the limit vacuum of 1.0* 10-1pa, and the two-stage mechanical pump can pump the container from the atmosphere to 6.7*10-2 pa, or even higher.

The exhaust gas rate is the volume of the gas that can be discharged in the unit time when the rotary pump is running according to the rated revolution. The formula can be used to calculate:

Sth = 2 NVS = 2 NFSL

Fs said finish inhaling cross-section of space-time cavity, the cavity length L said, coefficient of said rotor per rotation exhaust process twice a week, Vs said when the rotor in a horizontal position, finish inhaling, maximum volume, the space-time cavity speed for n.

The effect of the mechanical pump exhaust with the speed of the motor and the looseness of the belts have relationship, when the belt of motor is loose, motor speed is slow, mechanical pump exhaust effect will become worse, so often to maintain, the tally, also need to often check mechanical pump oil seal, oil is too little, can not meet the sealing effect, inside the pump leakage, oil too much, the suction hole plugging, inspiration and exhaust, generally, 0.5 cm in the oil level in the offline.

Booster pump and roots pump: it is to have a pair of synchronous high-speed rotating double leaf shape or lobed rotor mechanical pump, because it works the same as the roots blower, so also can call the roots vacuum pump, the pump in the range of 100-1 mpa pressure extraction speed greatly, it makes up for the mechanical pump exhaust ability insufficient shortcomings in this scope, the pump can't start work from the atmosphere, have no direct discharge of the atmosphere, its role is only to increase the differential pressure between inlet and outlet, the rest of the mechanical pump is needed to complete, therefore, it must match with mechanical pump as the backing pump.
 During the use of mechanical pump, the following problems must be paid attention to:

1. The mechanical pump should be installed in a clean and dry place.

2. The pump itself should be kept clean and dry. The oil in the pump is sealed and lubricated, so it should be added according to the regulations.

3. Replace the pump oil regularly, and replace the waste oil before it is replaced, and replace it at least three months to six months.

Connect the wires to the instructions.

5. Before the mechanical pump stops working, it is necessary to close the inlet valve, then power off and open the air valve, and put the atmosphere through the air inlet into the pump.

6. During the working period, the oil temperature can not exceed 75 degrees centigrade, or the oil will be too small to be sealed.

7. The belt looseness of the mechanical pump, the speed of the motor, the speed of the motor, and the sealing effect of the sealing ring are not required.

Oil diffusion pump: the limit 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 theory. If the high vacuum is to be obtained, the oil diffusion pump must be used.

Since the oil diffusion pump is the first to obtain high vacuum pump, it is very cheap, easy to maintain and widely used, so this article will focus on the discussion.

Scope of application of oil diffusion pump pressure is that palmer - 10 10-1-7, it is the use of gas diffusion phenomenon to exhaust, it has simple structure, convenient operation, large pumping speed (up to 10 + 5 liters per second), etc. Oil diffusion pump is mainly composed of pump body, nozzle, nozzle and heater, adding diffusion pump oil inside the main model is D - 704 # (Japan), based on what the nozzle can be divided into single-stage and multistage pump.

In the bottom of the diffusion pump, there is a diffusion pump oil. The upper part is the inlet port, and the lower part of the right side is the air outlet. At work, the air outlet is provided by the mechanical pump to provide the front pressure, and the mechanical pump ACTS as the front pump.

When the oil of the diffusion pump is heated by the electric furnace, the resulting 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 resulting oil vapor is ejected down the nozzle via the umbrella nozzle. Because of the vacuum of 1-10-1 pa provided by the mechanical pump outside the nozzle, the oil vapor can emit a distance, forming a jet that is moving in the direction of the air outlet. The efflux finally meets the wall of the pump cooled by cooling water, condenses into liquid and flows back to the evaporator, that is, the vaporization of the oil, the condensation, and the repeated cycle to achieve the extraction.

By the gas molecules in the air inlet into the pump, once fell into the steam flow, gets down the momentum of the movement down, because of the jet with high velocity (200 m/SEC), high density of the steam, and the diffusion pump oil with high molecular weight (300-500), it can effectively take gas molecules, so within the interface of jet, the gas molecules can't be stranded for a long time, and the jet flow on both sides of the interface, is the concentration of the smoke gas is very bad, just because of this concentration difference across the interface of action in the smoke gas diffusion into jet, was taken to the exit, and at the exit by the mechanical pump.

The oil vapor pressure of the diffusion pump is an important factor to determine the ultimate vacuum of the pump. Therefore, it is better to choose the pump oil with saturated vapor as low as possible.

The diffusion pump cannot be used alone to pump air. The maximum outlet pressure of the pump is 40 pa. Diffusion pump pumping victory is scheduled for the first level of the nozzle and the pump body of inlet diameter, the size of the circular area between pumping speed is not a constant value, but varies with the air inlet pressure, when pressure in 2 ~ 10-10-3, diffusion pump suction speed is the fastest, when the pressure is less than 5 * 10-4 mpa, diffusion pump suction speed minimum, almost no suction capacity (at this point, the inlet pressure is higher, because of its high density of air, make steam manifold become a high-speed jet to block the air diffusion, so the pumping speed down).

Diffusion pump to clean before installation, before they can load the diffusion oil, oil before heating, must first to the vacuum pump, diffusion pump oil cooling to the stop before you 60 to 70 degrees Celsius, can be closed before extraction, finally closed cooling water.

Because the oil diffusion pump is unable to put an end to return oil chance, so there is no way to guarantee precision products 100% pure, especially in the semiconductor industry, so there is a "high vacuum condensate pump + low vacuum mechanical pump" oil-free vacuum system, composed of the condensate pump exhaust system composed of not only exhaust efficiency is very high, and effectively guarantee the clean of the vacuum chamber, ensure the quality of the product (to avoid contaminated products, enhance the adhesion between coating and substrate), but its maintenance costs are very high, expensive, so there is no oil diffusion pump widely in penetration.

Cryogenic condensate pump: it is a kind of pump that USES low temperature surface to condensate gas molecules to achieve the exhaust gas. It is the highest vacuum pump with the highest vacuum and the highest pumping speed.

The working principle of condensing pump is mainly the condensation effect, cold trapping and physical low temperature adsorption of the cold surface.

Cryogenic condensation: it is cooled by liquid helium or refrigeration cycle helium, depending on the characteristics of various gases.

Cold trap, is no condensate gas is the phenomenon of condensable gas trap, usually of carbon dioxide, water vapor, nitrogen, compressed air and other gas first frost formation, in low temperature adsorption forms on the surface, thus achieve the purpose of other gases adsorption, cryogenic pumps in addition to the effect of the mixed gas smoke than in addition to the single effect is good it is for this reason.

Low temperature adsorption: refers to the effect of low temperature on the surface of the adsorbent adsorption gas, because of the adsorbent and the interaction between gas molecules is very strong, so can achieve the gas phase pressure than the condensation surface temperature under its saturated vapor pressure is low. Adsorbent is usually activated carbon.

Condensate pump rate of extraction and the extraction rates of the condensate pump has relationship with condensation on the surface of the area size, the data show that the unit condensation surface area of the extraction rate of 11.6 liters per second. Square centimeter, condensate pumps can be smoked to 10-8 mpa; In addition, the geometrical shape and position of adsorption surface of activated carbon, particle structure of activated carbon, bonding material and bonding process have a great influence on the speed of pumping. The second key is that the refrigerating machine must be large enough.

Vacuum gauge: vacuum gauge is an important part of vacuum coating machine. It is an important measure to detect vacuum degree of coating machine. The vacuum gauge can be divided into absolute vacuum gauge and relative vacuum gauge according to its working principle. The absolute vacuum gauge can measure the pressure directly, and the relative vacuum gauge can only measure the vacuum degree indirectly.

The following vacuum gauges commonly used in the coating machine:

Resistance vacuum gauge

It is mainly composed of electric heating wire, shell and bracket, mainly based on the heat conduction coefficient of the gas and the pressure proportional to the pressure. The upper opening is connected with the vacuum system under test. The hot wire is made of wire with large resistance temperature coefficient, and the two bracket leads are connected with the measuring line. When the pressure to reduce the quantity of heat of the gas heat conduction loss is reduced, so when the hot wire heating current is stable, the temperature of the wire is rising, the resistance of hot wire increases, by measuring the size of the resistance of the wire to indirectly measure the pressure, has the following relationship:

This is the working principle of resistance vacuum gauge, the vacuum gauge measuring range is: between the 100-10-1 mpa, is the WP - 02 models used at present

Magnetron discharge vacuum gauge

How it works: at the beginning of the discharge, because of the space, free electrons from the anode movement under the effect of orthogonal electromagnetic field, the electron trajectory is not straight line but spiral, and because the anode is frame, so the electronic not met for the first time the anode, but through the anode, and rejection by the cathode, and after return. This will be repeated many times before the anode is possible. Since the electronic distance is greatly extended, the number of collisions and ionization increases, which makes the discharge (also known as penning discharge) remain in the low pressure (10-4 pa).
 At present, more models have PKR251 and gi-pary.

Discharge tube vacuum gauge: two metal electrodes sealed in a glass tube, on top of it plus a few kv dc high voltage, in a certain range of pressure (10-3 ~ 1 * 2 * 10) can cause self sustaining discharge, discharge color to determine its vacuum degree

So far this kind of vacuum gauge has been used very little, because its error is large, easy to damage, and life is not long.

Evaporation system

Evaporation system mainly refers to the film forming device, coating machine into membrane device is very much, have a resistance heating, electron gun evaporation, magnetron sputtering, rf sputtering, ion plating, such as a variety of ways, I resistance heating and gun evaporation introduce two kinds of way, because of this I used more in one of two ways.

Resistance evaporation, based on its structure and working principle, is by far the most widely used and the most widely used evaporation method. The way it works is that the tungsten as a ship, and then installed in the middle of the two electrodes, in the middle of the tungsten boat with herbs, again slowly to the electrode current, current through the tungsten, tungsten boat electric heating, the low voltage, high current make tungsten boat to generate heat, high melting point and heat transfer to the coating material, when the quantity of heat of tungsten boat is higher than the melting point of coating material, material sublimation or vaporization, this method because of easy operation, simple structure, low cost, so is a lot of equipment used, but the evaporation of thin film because of the low density, plus a lot of material can't use this way to evaporation, so it has certain limitations. The melting point of the material must be less than the melting point of the tungsten boat, otherwise there is no way to do it.

Gun evaporation is by far the most a evaporative way, it can evaporate any a kind of coating material, the way it works is that: the coating material in the crucible, the evaporation source into a filament shape, using a special control cabinet, the filament with a strong current, high voltage, due to the material is tungsten filament, so it will be hot, in the end will launch electronic, and adoption of a certain magnetic field will be gathered into a certain shape, and drawing on the crucible, thus formed a beam, due to the electron temperature is very high, can melt any coating materials, as the coating materials is after electron beam melting (some of the material is directly sublimate), medicinal herbs of molecules (atoms or ions) in a vacuum into linear motion, then meets the base board, and then condense, growth through this way, form a film! The most commonly used is the deflection Angle of the electron beam.

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