Chemical vapor deposition (CVD) is a kind of chemical technology, which mainly uses one or several gaseous compounds or simple substances containing film elements to carry out chemical reaction on the substrate surface to generate films.Chemical vapor depositionIt is the preparation developed in recent decadesInorganic materialsNew technology.Chemical vapor deposition has been widely used to purify substances, develop new crystals, and deposit various single crystals, polycrystals, orGlassy stateinorganicFilm material。These materials can be oxides, sulfidesnitrides、carbide, or III-VII-IV, IV-VI family of binary or multi-component intermetallic compounds, and their physical functions can be precisely controlled by the vapor doped deposition process.Chemical vapor deposition has become a new field of inorganic synthetic chemistry.
Chinese name
Chemical vapor deposition
Foreign name
Chemical VaporDeposition
Abbreviation
CVD
Nature
A chemical technology
Used as
Purifying substances, developing new crystals, depositing various single crystals, polycrystals orGlassy stateInorganic film materials
Modern science and technology need to use a large number of new inorganic materials with different functions. These functional materials must be high-purity, or doped materials formed by deliberately mixing some impurities into high-purity materials.However, many preparation methods we were familiar with in the past, such as high-temperature meltingaqueous solutionMedium precipitation and crystallization are often difficult to meet these requirements, and it is also difficult to ensure high purity products.Therefore, the synthesis of new inorganic materials has become a major topic in modern materials science.[1]
principle
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Chemical vapor deposition (CVD) is a process that uses gaseous substances to generate chemical reactions and transport reactions on solids and produce solid deposits. It roughly includes three steps:
(1) Formation of volatile substances;
(2) Transfer the above substances to the sedimentary area;
(3) Produce chemical reactions on solids and produce solid substances.
The most basic chemical vapor deposition reactions includeThermal decomposition reaction, chemical synthesis reaction and chemical transport reaction.[1]
characteristic
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1) At medium or high temperature, solid substances are deposited on the substrate through the vapor phase chemical reaction between the initial gaseous compounds.
2) You can use theAtmospheric pressureOr under vacuum conditions (negative pressure "for deposition, usually the quality of vacuum deposition film is better).
3) Plasma and laser assisted technology can significantly promote chemical reaction, so that deposition can be carried out at a lower temperature.
4) The chemical composition of the coating can change with the change of gas phase composition, so as to obtain gradient deposit or mixed coating.
5) The density and purity of the coating can be controlled.
6) Good winding and plating performance.Can be used in complex shapematrixAnd coating on granular materials.Suitable for coating workpieces of various complex shapes.Because of its good coating performance, it can be used to coat workpieces with grooves, grooves, holes, or even blind holes.
7）Sedimentary layerIt usually has columnar crystal structure and is not resistant to bending, but it can bechemical reactionGas phase disturbance is carried out to improve its structure.
8) Various metal, alloy, ceramic and compound coatings can be formed through various reactions.[2]
Type of technology
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The reactor is the main component of the chemical vapor deposition device.According to the difference in reactor structure, we can divide chemical vapor deposition technology into two types: open tube/closed tube gas flow method:
1 Pipe sealing method
This reaction method is to place a certain amount of reactants and collectives on both sides of the reactor, vacuum the reactor, inject some transport gas into it, seal it again, and then control the temperature at both ends of the reactor to make it different. Its advantages are: ① it can effectively avoid external pollution; ②It can keep the vacuum inside without continuous pumping.Its disadvantages are: ① slow production of materials; ②The pressure in the pipe is not easy to master.
2 Pipe opening method
The feature of this preparation method is that the reaction gas mixture can be supplemented at any time.Waste gas can also be discharged from the reaction device in time.According to the heating method, the open tube airflow method should be divided into hot wall and cold wall methods.The heating of the former will heat the whole wall of the deposition chamber, so deposition will also occur on the pipe wall.In the latter case, only the body itself will be heated, so there is no such disadvantage.Cold wall heating generally uses induction heating, power on heating and infrared heating.[1]
Application of chemical vapor deposition technology in material preparation
Chemical vapor deposition can not only improve the properties of crystals or crystal films, but also produce some crystals that cannot be prepared by other means.The most common use of chemical vapor deposition is to generate a new epitaxial single crystal layer on a crystal substrate. At first, it was used to prepare silicon, and then epitaxial layers were preparedCompound semiconductorLayer.It is also common in the preparation of metal single crystal thin films (such as the preparation of WMo, Pt, Ir, etc.) and individual compound single crystal films (such as nickel ferrite films, yttrium iron garnet films, cobalt ferrite films, etc.).
2 Production of whiskers
Whisker is a kind of single crystal that is developed. It plays a great role in the field of composite materials and can be used to produce some new composite materials.The chemical vapor deposition method uses the hydrogen reduction property of metal halides in the production of whiskers.Chemical vapor deposition can not only produce various kinds of metal whiskers, but also produce compound whiskers, such as alumina, emery, titanium carbide whiskers, etc.
Production of Polycrystalline/Amorphous Material Films by Chemical Vapor Deposition
Chemical vapor deposition (CVD) is widely used in semiconductor industry.For example, the polysilicon deposition layer serves as the edge medium isolation layer.In the contemporary era, more and more new types of micro electronic components are usedAmorphous material, which includes phosphor silicon glassBorosilicate glass、SiOtwoAnd SithreeNfourwait.In addition, some may be developed into switches and memory materials in the future, such as copper oxide-Phosphorus pentoxideCopper oxide-Vanadium pentoxide-Phosphorus pentoxide and vanadium pentoxide phosphorus pentoxide can be produced by chemical vapor deposition.[1]
Application of Chemical Vapor Deposition in Precious Metal Materials
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Production of several precious metal films by chemical vapor deposition
Precious metal thin films have attracted researchers' interest because of their good oxidation resistance, high conductivity, strong catalytic activity and extremely stable.Compared with other methods of producing precious metal films, chemical vapor deposition has more technical advantages, so most of them will use this method to prepare precious metal films.Depositors used to deposit precious metal films have a wide range of materials, but most of them are halides and organic compounds of precious metal elements, such as COCltwo, carboyl platinum chloride, carboyl iridium chlorideDCPD compounds, etc.
Goto team has done a lot of work on using precious metal films as electrode materials.The substrate materials they use include sapphirequartz glassAnd yttrium oxide stabilizedZirconia(YSZ) and so on.When depositing, oxygen is introduced into the device to eliminate the carbon produced by thermal decomposition of raw materials and prepare moreMetallic lusterIf not, the final result is iridium carbon cluster film, that is, iridium particles wrapped in the crystal carbon layer at the nanometer level.Iridium carbon cluster films deposited on YSZ have excellent electrical properties and catalytic activity.At relatively low temperatures, the interfacial conductivity of iridium carbon cluster films can be more than 100 times that of pure iridium or pure platinum.The cluster membrane composed of precious metals and carbon is a kind of transport porous cluster membrane with strong catalytic activity, and its application in electrode materials will have great potential in the future.
Production of precious metal iridium high temperature coating by chemical vapor deposition
Since the 1980s,NASA began to try to useOrganometallic chemical vapor depositionThe composite nozzle coated with rhenium based iridium was successfully taken out by the chemical vapor deposition methodMetallic coatingA breakthrough has been made in the field to a certain extent.
NASA used CfifteenHtwenty-oneIrOsixAs a material for preparing iridium coating, CfifteenHtwenty-oneIrOsixThermal decomposition reaction.The deposition rate of iridium is very fast, up to 3~20 μ m/h.The deposition thickness also reached 50 μ m,CfifteenHtwenty-oneIrOsixThe production efficiency of is more than 70%.
3 Palladium chemical vapor deposition
Pd and its alloys have strong adsorption and special selective permeability to hydrogen, and are ideal materials for hydrogen storage or purification.Pd is mostly used to produce hydrogen purification equipment from palladium alloy or palladium coating.Some scholars use chemical vapor deposition to make palladium thin films or thin layers.The specific method is to use the extremely low decomposition temperatureOrganometallic compoundAs a material for preparing palladium, it specifically includes: allyl [β - ketoimine] Pd (Ⅱ)Pd（η-CthreeHfive） （η-CfiveHfive）And Pd (η - CthreeHfive）（CFthreeCOCHCOCFthree）Such materials can be used to prepare palladium films with high purity.
Chemical vapor deposition (CVD) technology is an important method of material preparation, which plays an important role in precious metal films and coatings. At present, China is still in the development stage in the aerospace field, and the use of CVD technology still has a lot of exploration space, which requires us to invest more energy in research.[1]
