Electron beam evaporation
Evaporation Technology - Electron Beam Evaporation
Vacuum Evaporation Coating: A process in which a solid material is heated in a high vacuum environment to sublimate or evaporate and deposit on a specific substrate to obtain a film.
Vacuum evaporation technology classification:
Resistance thermal evaporation
2. Electron beam evaporation
3. High frequency induction evaporation
4. Laser beam evaporation
A commonly used resistance heating evaporation method is to place the material to be evaporated in a resistance heating device, and the resistance heating in the circuit supplies the evaporation heat to vaporize the material to be deposited. In this method, the commonly used supporting heating materials are refractory metals such as tungsten, tantalum and molybdenum, all of which have high melting point and low vapor pressure characteristics. The support heating material generally takes the form of a filament or a foil.
As shown, the heating device is made of thin tungsten/molybdenum wire (0.05-0.13 cm in diameter). The evaporant is placed directly on the filament heating device. When heated, the evaporant wets the resistance wire and is supported by surface tension. A typical wire with multiple strands provides a larger surface area than a single strand. This type of heating device has four major drawbacks:
(1) They can only be used for the evaporation of metals or certain alloys:
(2) Only a limited amount of evaporated material is evaporated during a certain period of time:
(3) When heating, the evaporation material must wet the resistance wire:
(4) Once heated, these electric filaments become brittle and will break if not handled properly.
The concave foil is made of a sheet of tungsten, tantalum or molybdenum and has a thickness generally ranging from 0.005 to 0.015 inches. This evaporation source device is most suitable when there is only a small amount of evaporation material. When heated in a vacuum, tungsten, tantalum or molybdenum will become brittle, especially when they are alloyed with the evaporation material.
The main disadvantages of electric yang heating evaporation are:
(1) The support crucible and the material react with the evaporant.
(2) It is difficult to obtain a sufficiently high temperature to evaporate dielectric materials such as A1203, Ta2O5, TiO2, and the like.
(3) The evaporation rate is low.
(4) The alloy or compound will decompose when heated.
Electron beam evaporation: A method in which an evaporation material is placed in a water-cooled crucible, and directly heated by an electron beam to vaporize the evaporation material and condense on the substrate to form a thin film.
The disadvantage of evaporation by resistance heating is that the method is not suitable for evaporation of high-purity or high-melting substances, and electron beam evaporation can overcome this deficiency of resistance evaporation, and thus electron beam heating has become an evaporation high-melting film and high purity. A major method of film. In electron beam evaporation technology, a beam of electrons is accelerated after passing an electric field of 5-10 kV.
Finally focus on the surface of the material to be evaporated. When the electron beam hits the surface of the material to be evaporated, the electrons will quickly lose their energy, transfer the energy to the material to be evaporated to melt and evaporate, that is, the surface of the material to be evaporated is directly heated by the colliding electron beam. The heating method is very different.
Since the evaporating material in contact with the crucible containing the material to be evaporated remains solid throughout the evaporation deposition process, the possibility of the material to be evaporated reacting with the crucible is minimized. Evaporation of materials in water-cooled crucibles directly by electron beam heating is a common method in electron beam evaporation. For the evaporation of active materials, especially active refractory materials, water cooling of the crucible is necessary. By water cooling, the reaction between the evaporation material and the crucible wall can be avoided, whereby a high-purity film can be prepared.
In the electron beam evaporation system, the device that generates the electron beam becomes an electron gun. According to different electronic focusing methods, the electron gun can be divided into a ring gun, a straight gun, and an e-gun.
The ring gun emits an electron beam from a ring-shaped cathode, which is deflected by the cathode ring and then hits the 坩埚 (
The material is evaporated in the anode) as shown in the structural section. Ring gun type structure is simple, cost
Low, easy to use. However, because the cathode of the ring gun is very close to the anode, it is easy to break down.
The wire is also easily contaminated; at the same time, the spot position of the electron beam is fixed, and it is easy to appear
Pit" Evaporation. Because the power and efficiency of the ring gun is not high, it has been used less.
Advantages: simple structure, low cost and easy to use
Disadvantages: Filament easy wave pollution
Spot fixation is prone to "pit" evaporation
Power and efficiency are not high
A straight gun is an axisymmetric linear acceleration gun. The electron beam emitted from the heating filament is accelerated by the anode and then focused by a magnetic field, and then bombarded with the material in the crucible to melt and evaporate. Among them, the action of the xy deflection coil It is to make the focused electron beam move in a small range, so that the position of the focus spot can be adjusted.
Advantages: easy to use; wide power range (several hundred watts to several hundred dry watts) easy to adjust
Disadvantages: The equipment is bulky, the structure is complex, and the cost is high: the evaporation of the village material will pollute the structure of the gun body, and the sodium ions escaping on the filament will cause the film to stain.
The e-gun is an electron gun that deflects the electron beam by 270° and is named after the electron trajectory is "e" shaped.
The electron beam emitted from the filament is accelerated by a bias voltage of several thousand volts and tapped
After the magnetic field is deflected by 270°, the evaporating material in the crucible is bombarded to melt and evaporate.
Advantages: Avoid contamination of the filament by the evaporation material and contamination of the filament by thin filament
High power (about 10kW). Evaporable high melting point
The energy of evaporating particles is high, the adhesion of the film to the substrate is large, and the film forming quality is good.
Disadvantages: high vacuum is required, and high voltage equipment is required. The structure of the equipment is complicated, it is difficult to maintain, and the equipment cost is high.
The advantages of electric beam evaporation are as follows: (1) It can directly heat the evaporation material, reduce heat loss, and has higher thermal efficiency: (2) The energy density generated by the electron beam is large, and the material with high melting point (greater than 3000 ° C) can be evaporated. , and has a higher evaporation rate: (3) The crucible containing the evaporation material is cold or cooled with water, which can avoid the reaction of the evaporation material and the evaporation of the container material, thereby improving the purity of the film.
The disadvantages are as follows: (1) The heating device is complicated: (2) The residual gas molecules in the straight space and the vapor of the partially evaporated material are ionized by the electron beam, which may affect the structure and physical properties of the film.
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