PVD and CVD vacuum coating technology and system
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Vacuum coating is an important aspect of vacuum application field, it is based on vacuum technology, the use of physical or chemical methods, and the absorption of electron beam, molecular beam, ion beam, ionic beam, radio frequency and magnetic control and a series of new technologies, scientific research and practical production of film preparation to provide a new process. To put it simply, the method of vaporizing or sputtering a metal, alloy or compound in a vacuum to solidify and deposit it on the coated object (called substrate, substrate or matrix) is called vacuum coating.
As is known to all, on the surface of some materials, as long as the coating of a thin film, the material can have many new, good physical and chemical properties. In the 1970s, the main methods of coating on the surface of objects were electroplating and electroless plating. The former is through electricity, electrolyte electrolysis, electrolytic ion plating as another electrode substrate surface, so the condition of this coating, the substrate must be a good conductor of electricity, and the thickness of the film is difficult to control. The latter is to use chemical reduction method, must be prepared into a solution of membrane material, and can quickly participate in the reduction reaction, this coating method not only the film binding strength is poor, and the coating is neither uniform nor easy to control, but also produce a lot of waste liquid, causing serious pollution. Therefore, these two kinds of coating process, which is called wet coating method, are greatly restricted.
Vacuum coating is a new kind of coating technology developed relative to the wet coating method, which is usually called dry coating technology.
Vacuum coating technology is generally divided into two categories, namely physical vapor deposition (PVD) technology and chemical vapor deposition (CVD) technology.
Physical vapor deposition technology refers to the method of vaporizing the plating material into atoms, molecules or ionizing it into ions and directly depositing them on the surface of the substrate under vacuum conditions by various physical methods. Most hard reaction films are prepared by physical vapor deposition method, which utilizes some physical processes, such as the thermal evaporation of substances or sputtering of atoms on the surface of substances under ion bombardment, to realize the controllable transfer of atoms from the source material to the thin film. Physical vapor deposition technology has the advantages of good film/base adhesion, uniform and dense film, good controllability of film thickness, wide application of target materials, wide sputtering range, depositable thick film, stable composition of alloy film and good repeatability. At the same time, physical vapor deposition technology due to its processing temperature can be controlled under 500 ℃, thus can be used as the final treatment process for high speed steel and carbide class film cutter. As the physical vapor deposition process can greatly improve the cutting performance of cutting tools, people are competing to develop high performance and high reliability equipment at the same time, but also to the expansion of its application field, especially in the application of high-speed steel, cemented carbide and ceramic tools in a more in-depth study.
Chemical vapor deposition technology is the elemental gas containing a membrane element or compound supply base, with the aid of the gas phase or substrate on the surface of a chemical reaction, on the matrix method of making metal or compound film, mainly including atmospheric pressure chemical vapor deposition, low pressure chemical vapor deposition and has both features of CVD and PVD plasma chemical vapor deposition, etc.
Compared with wet coating technology, vacuum coating technology has the following advantages:
(1) wide selection of film and matrix materials, film thickness can be controlled to prepare functional films with various functions.
(2) the preparation of thin films under vacuum conditions, the environment is clean, the film is not easy to be polluted, so the film with good density, high purity and uniform coating can be obtained.
(3) the film has good bonding strength with the matrix and is firm.
(4) dry coating neither produces waste liquid, nor environmental pollution.
Vacuum coating technology mainly includes vacuum evaporation plating, vacuum sputtering plating, vacuum ion plating, vacuum beam deposition, chemical vapor deposition and other methods. In addition to chemical vapor deposition, other methods have the following common characteristics:
(1) all kinds of coating technologies need a specific vacuum environment to ensure that the movement of vapor molecules formed in the heating evaporation or sputtering process of film-making materials will not be affected by the collision, blocking and interference of a large number of gas molecules in the atmosphere, and the adverse effects of impurities in the atmosphere will be eliminated.
(2) various coating technologies require an evaporating source or target to convert the evaporating film-making material into gas. Due to the continuous improvement of source or target, the selection range of film-making materials has been greatly expanded. No matter metal, metal alloy, intermetallic compound, ceramic or organic material, all kinds of metal film and dielectric film can be steamed and plated, and multi-layer film can be obtained by steaming and plating different materials at the same time.
(3) the film thickness of evaporation or sputtering film making materials can be accurately measured and controlled in the process of forming film with the workpiece to be plated, so as to ensure the uniformity of film thickness.
(4) each film can accurately control the composition and mass fraction of residual gas in the coating chamber through fine-tuning valve, so as to prevent oxidation of evaporation materials, reduce the mass fraction of oxygen to the minimum, but also can be filled with inert gas, etc., which is impossible to achieve for wet coating.
(5) due to the continuous improvement of coating equipment, coating process can achieve continuous, thus greatly improving the output of products, and in the production process of environmental pollution.
(6) as the film is made in a vacuum condition, the film has high purity, good compactness and bright surface without any further processing, which makes the mechanical and chemical properties of the film better than electroplating film and chemical film.
Vacuum coating methods are many, including:
(1) vacuum evaporation: the substrate to be coated shall be cleaned and put into the coating chamber. After being evacuated, the membrane material shall be heated to a high temperature to make the vapor reach about 13.3pa and the vapor molecules shall fly to the surface of the substrate and coagulate to form the film.
(2) cathode sputtering: put need coating substrate opposite the cathode, access to the inert gas such as argon) has to indoor, to keep the pressure is about 1.33 ~ 13.3 Pa, the cathode can then be connected to 2000 v dc power supply, and stimulate the glow discharge, positively charged argon ion collision cathode, make its injection atomic, sputtering out of atoms by membrane is formed on the inert atmosphere to the substrate.
(3) chemical vapor deposition: the process of depositing thin films by thermal decomposition of selected metal compounds or organic compounds.
(4) ion plating: in fact, ion plating is an organic combination of vacuum evaporation and cathode sputtering, which has both technical characteristics
1. The vacuum chamber
Coating equipment mainly has two forms of continuous coating production line and single-chamber coating machine, stainless steel material manufacturing, argon arc welding, surface chemical polishing treatment, vacuum chamber components welding flange interface of various specifications.
2. Vacuum acquisition part
Vacuum acquisition is an important part of vacuum technology. The acquisition of vacuum is not a vacuum equipment and methods can be achieved, must be a combination of several pumps, such as mechanical pump, roots pump, molecular pump system.
3. Vacuum measurement part
The vacuum measurement part of the vacuum system is to measure the pressure in the vacuum room. Like vacuum pumps, no vacuum gauge can measure the entire vacuum range, so people make many kinds of vacuum meters according to different principles and requirements. Such as thermocouple meter, ionization meter, pirani meter and so on.
4. Power supply part
The target power supply mainly includes dc power supply, if power supply, pulse power supply, RF power supply (RF), common power supply manufacturers have AE,ADL, hotinger and so on.
5. Process gas input system
Process gas, such as argon (Ar), krypton (Kr), nitrogen (N2), acetylene (C2H2), methane (CH4), hydrogen (H2), oxygen (O2), etc., are generally supplied by the cylinder, through the gas pressure reducing valve, gas globe valve, pipeline, gas flow meter, electromagnetic valve, piezo valve, and then into the vacuum chamber. The advantage of this gas input system is that the pipeline is simple, bright, easy to repair or replace the cylinder. Each coating machine does not affect each other. There are also cases where multiple coating machines share a set of cylinders, which may be seen in some larger coating workshops. Its advantage is, reduce gas cylinder to occupy dosage, unified plan, unified layout. The disadvantage is that the number of connections increases the chance of air leakage. And, each coating machine will interfere with each other, a coating machine pipe leakage, may affect the quality of other coating machine products. In addition, when replacing the gas cylinder, you must ensure that all the machines are in a non-gas state.
6. Mechanical transmission part
The coating requires uniform thickness around the coating, so there must be three rotations in the coating process to meet the requirements. That is, when the large workpiece table is required to rotate (I), the small workpiece bearing table also rotates (II), and the workpiece itself can rotate simultaneously (III). In mechanical design, it is generally in the center of the bottom of the large workpiece turntable for a large driving gear, surrounded by a number of small star gear meshing with it, if you want to achieve product rotation, generally use a fork to dial the workpiece rotation.
7. Heating and temperature measuring parts
Coating equipment generally have different positions of the heater, thermocouple measurement and control temperature. However, since the position of thermocouple clamping is different from that of the workpiece, the temperature reading cannot be the real temperature of the workpiece. To measure the real temperature of the workpiece, there are many ways, you can install a high temperature test paper or thermocouple meter on the workpiece.
8. Ion evaporation and sputtering sources
The evaporation source of multi-arc plating is generally round cake, commonly known as round cake target, but also rectangular multi-arc target. The target seat is equipped with a magnet. By moving the magnet back and forth, the magnetic field intensity can be changed and the moving speed and track of the arc spot can be adjusted. In order to reduce the temperature of the target and the target seat, the target seat should be continuously fed with cooling water. In order to ensure the high conductivity and thermal conductivity between the target and the target seat, tin gaskets can be added between the target and the target seat. Magnetron sputtering films generally use rectangular or cylindrical sputtering cathode.
9. Water cooling system
Generally by the cold water tower, ice water machine, water pump, etc.
10. Industrial control system