Chemical vapor deposition refers to chemical vapor depositionGaseous reactantorLiquid reactantAnd other gases required for reactionReaction chamber, onsubstrateGenerated by chemical reaction on the surfacefilmProcess.stayvlsiMany thin films are prepared by CVD method.
Chinese name
Chemical vapor deposition
Foreign name
Chemical Vapor Deposition
Raw materials
Gaseous reactantorLiquid reactantVapor of
Application
Preparation of new inorganic materials
Features
Low deposition temperature, easy to control film composition
Chemical vapor deposition consists ofFilm elementOf gaseous reactant is introduced into the reaction chamber and occurs on the wafer surfacechemical reactionTo generate the requiredSolid filmAnd deposited on its surface.[1]
staychipMost of the requiredFilm material, whetherconductor、semiconductor, orDielectric material, can be prepared by chemical vapor deposition, such assilica film 、Silicon nitride film、polysilicon film Etc.It hasDeposition temperatureLow, easy to control film composition and thicknessDeposition timeProportional, good uniformity and repeatability, good step coverage, easy operation, etc.Low deposition temperature and good step coveragevlsiThe manufacturing of is very advantageous.So it'sIntegrated circuitThe most important film deposition method in the production process.Commonly used areAtmospheric pressure chemical vapor deposition、Low pressure chemical vapor depositionas well asPlasma enhanced chemical vapor depositionEtc.
principle
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CVD is a process that uses gaseous substances to carry out chemical reactions on the solid surface to generate solid deposits.It generally includes three steps:
(1) Produce volatile substances;
(2) Transporting volatile substances to sedimentary areas;
(3) The chemical reaction takes place on the matrix to generate solid products.[2]
Figure 1 Schematic Diagram of CVD Reaction System
Technical classification
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Reactor is the most basic component of CVD device.According to different reactor structures, CVD technology can be divided into two basic types: open tube airflow method and closed tube airflow method.
Pipe sealing method
This reaction system is to place a certain amount of reactants and appropriate matrix at both ends of the reactor respectively, fill a certain amount of transport gas into the tube after vacuumizing, then seal, and then place the reactor in a dual temperature zone, so that a temperature gradient is formed in the reaction tube.The negative free energy change caused by the temperature gradient is the driving force of the transfer reaction, so the material is transferred from one end of the sealed pipe to the other and deposited.
The advantages of the sealing method are: (1) it can reduce the pollution from the outside;(2) Vacuum can be maintained without continuous pumping;(3) High conversion rate of raw materials.Its disadvantages are: (1) the material growth rate is slow, which is not conducive to mass production;(2) Sometimes the reaction tube can only be used once, and the deposition cost is high;(3) It is difficult to measure the pressure in the pipe, which is dangerous.
Open tube method
The characteristic of open tube gas flow method is that the reaction gas mixture can be continuously supplemented, and the waste reaction products can be continuously discharged from the sedimentation chamber.According to the different heating methods, the open tube airflow method can be divided into hot wall type and cold wall type.The hot wall reactor is generally heated by a resistance heating furnace, and the chamber wall and substrate of the deposition chamber are heated. Therefore, the disadvantage of this heating method is that deposition will also occur on the tube wall.In the cold wall reactor, only the substrate itself is heated, so only the hot substrate will deposit.The common methods to realize cold wall heating include induction heating, power on heating and infrared heating.[2]
Technical characteristics
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The film formed by chemical vapor deposition (CVD) technology is compact and uniform, the combination between the film and the substrate is firm, the film composition is easy to control, the deposition speed is fast, the film quality is also very stable, and some special films also have excellent optical, thermal and electrical properties, so it is easy to achieve mass production.
However, the deposition temperature of CVD is usually very high, between 900 ℃ and 2000 ℃, which is easy to cause part deformation and structural changes, thus reducing the mechanical properties of the body material and weakening the bonding force between the body material and the coating, so that the selection of the substrate, the deposition layer or the quality of the resulting workpiece are restricted.
CVD technology is developing in the direction of medium, low temperature and high vacuum, and combining with plasma, laser, ultrasonic and other technologies, many new CVD technologies have been formed.[3]
Technology application
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Protective coating field
Materials used in many special environments often need coating protection to make them wear resistant, corrosion resistant, high-temperature oxidation resistant and radiation resistant.TiN, TiC, Ti (C, N) and other thin films prepared by CVD method have high hardness and wear resistance. The service life of the tool can be increased by more than three times if only 1~3 μ m TiN film is coated on the cutting surface of the tool.Othersmetallic oxide, carbide, nitride, silicide, phosphide, cubic boron nitride, diamond-like carbon and other films, as well as various composite films also show excellent wear resistance.In addition, Al2O3, TiN and other thin films obtained by deposition have good corrosion resistance, while amorphous containing chromium has higher corrosion resistance.Silicon compounds such as SiC, Si3N4 and MoSi2 are very important high-temperature oxidation resistant coatings. These coatings generate dense SiO2 films on the surface and can resist oxidation at 1400~1600 ℃.Mo and W CVD coatings also have excellent high-temperature corrosion resistance, which can be applied to turbine blades, rocket engine nozzles and other equipment parts.Some ion plated Al, Cu, Ti and other films have been used on parts of aviation industry instead of electroplated products.The hot corrosion resistant and alloy coatings prepared by vacuum coating and the further developed thermal barrier coatings have been used in many series in production.
Microelectronics technology
In the basic manufacturing process of semiconductor devices and integrated circuits, the epitaxy of semiconductor films, the formation of p-n junction diffusion elements, dielectric isolation, the deposition of diffusion masks and metal films are the core process steps.Chemical vapor depositionIn the process of preparing these material layers, the old processes such as high temperature oxidation and high temperature diffusion of silicon have gradually replaced, and play a leading role in modern microelectronics technology.stayvlsiIn production, chemical vapor deposition can be used to deposit polysilicon film, tungsten film, aluminum filmMetal silicide, silicon oxide film, silicon nitride film, etc. These film materials can be used as gate electrode, interlayer insulation film of multi-layer wiring, metal wiring, resistance, heat dissipation materials, etc.
Superconducting technology
The superconducting material prepared by CVD isRadio America(RCA) invented in the 1960s, the Nb3Sn low-temperature superconducting tape produced by chemical vapor deposition has dense coating, easy thickness control, and good mechanical properties. It is the best material for firing small magnets with high field strength.In order to improve the superconductivity of Nb3Sn, many countries have done a lot of research work in doping, baseband materials, dehydrogenation, heat treatment and copper (silver or aluminum) plating stability, making the CVD method one of the main production methods of commercial Nb3Sn superconducting tapes.Now usedChemical vapor depositionOther metal rooms producedsuperconducting compound There are also Nb3Ge, V3Ga, Nb3Ga, etc.
Solar energy utilization field
Solar energy is inexhaustibleInorganic materialsIt is an important way to use solar energy to make solar cells with the photoelectric conversion function of.CVD technology, including LPCVD and PCVD, is often used to prepare polycrystalline silicon thin film batteries.The silicon and gallium arsenide homojunction cells that have been successfully trial produced, as well as a variety of heterojunction solar cells made of II-V, I-VI and other semiconductors, such as SiO2/Si, GaAs/GaAlAs, Cd Te/CdS, are almost all made into thin films. Vapor deposition is their main preparation technology.[3]
Development prospect
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With the continuous improvement of industrial production requirements, the process and equipment of CVD have been continuously improved. More new films have been obtained, and the performance and quality of the films have been greatly improved.At the same time, the cross and comprehensive use of composite methods not only enables various new heating sources, but also makes full use of various chemical reactions, high-frequency electromagnetic (pulse, radio frequency, microwave, etc.), plasma and other effects to activate the deposited ions, which has become an important way of technological innovation.
CVD technology has a wider range of applications due to the use of plasma, laser, electron beam and other auxiliary methods to reduce the reaction temperature. The next step should be to reduce harmful products and increase the scale of industrial production.At the same time, the lower temperature of CVD reaction deposition temperature, the more accurate control of the composition, structure, morphology and performance of materials with CVD, the development of thick film coating technology, the use of residual stress to improve the strength of materials, the preparation technology of large continuous CVD films and coatings, the synthesis technology of new materials, the development of reactors with new structures,The exploration of new coating materials and new and more powerful material systems will become the main research topic in the future.[3]
