Introduction
1. Metal organic compound chemical vapor deposition technology (MOCVD)
MOCVD is a method of chemical vapor deposition that utilizes metal organic compounds that are easily decomposed and volatile at low temperatures as a material source, mainly used for the vapor phase growth of compound semiconductors. Compared with traditional CVD, MOCVD has a relatively lower deposition temperature and can deposit special structured surfaces such as ultra-thin layers or even atomic layers, allowing for the deposition of different thin films on different substrate surfaces. Therefore, it has high application value for substrates that cannot withstand conventional CVD high temperatures and require the use of medium to low temperature substrates, such as steel. In addition, polycrystalline SiO2 grown by MOCVD technology is a good transparent conductive material, and TiO2 crystalline films obtained by MOCVD have also been used in anti reflection layers, water photoelectrolysis, and photocatalysis of solar cells. The most attractive new application of MOCVD technology is the preparation of novel high-temperature superconducting oxide ceramic thin films.
2. Plasma Chemical Vapor Deposition (PCVD)
Plasma enhanced chemical vapor deposition, also known as plasma enhanced chemical vapor deposition, is a process that utilizes low-temperature plasma generated by gas glow discharge to enhance the chemical activity of reactants, promote chemical reactions between gases, and deposit high-quality coatings at lower temperatures.
At present, PCVD is mainly used on substrates such as metals, ceramics, and glass as protective films, reinforcement films, modification films, and functional films. The important new progress in its application is the deposition of diamond-like carbon films, which are generally prepared by combining radio frequency plasma hydrocarbon gas decomposition and ion beam deposition. These ceramic films have unique application prospects in the fields of wear-resistant coatings for cutting tools, laser reflectors, optical fiber films, etc.
3. Laser Chemical Vapor Deposition (LCVD)
LCVD is a thin film deposition method that utilizes the photon energy of a laser beam to excite and promote chemical reactions during the chemical vapor deposition process. At present, LCVD technology is widely used in laser lithography, correction of large-scale integrated circuit masks, laser evaporation deposition, and metallization. The LCVD method for silicon nitride film has reached the level of industrial application, with an average hardness of up to 2200HK.
4. Low pressure chemical vapor deposition (LPCVD)
The pressure range of LPCVD is generally between 1 × 104 and 4 × 104 Pa. Due to the increase in the average free path of molecules under low pressure, the mass transfer rate of gaseous reactants and by-products is accelerated, thereby accelerating the reaction rate of forming deposited thin film materials. Meanwhile, the uneven distribution of gas molecules can be eliminated in a short period of time, allowing for the growth of thin films with uniform thickness. In addition, during the transportation of gas molecules, the reactant molecules participating in chemical reactions absorb a certain amount of energy at a certain temperature, which activates these molecules and puts them in an activated state. This makes it easy for chemical reactions to occur between the reactant gas molecules participating in chemical reactions, which means that the deposition rate of LPCVD is relatively high. This method can be used to deposit polycrystalline silicon, silicon nitride, silicon dioxide, etc.
5. Ultra vacuum chemical vapor deposition (UHVCVD)
In another development direction of CVD - high vacuum, ultra-high vacuum chemical vapor deposition (UHVCVD) method has emerged. Its growth temperature is low (425-600 ℃), but it requires a vacuum degree of less than 1.33 × 10-8Pa. The design and manufacturing of the system is easier than molecular beam epitaxy (MBE), and its advantage is the ability to achieve multi wafer growth. The design and manufacturing of the reaction system is also not difficult. Unlike traditional epitaxy, this technique uses low voltage and low temperature growth, making it particularly suitable for depositing semiconductor materials such as Sn: Si, Sn: Ge, Si: C, Gex: Si1-x, etc.
6. Ultrasonic Chemical Vapor Deposition (UWCVD)
Ultrasonic chemical vapor deposition emerged in the search for high-energy energy sources that initiate CVD in a radiation form different from electromagnetic waves. Ultrasonic waves can improve the deposition rate of CVD and form smooth and uniform deposition films that traditional CVD cannot obtain. According to relevant reports, adjusting the frequency and power of ultrasound appropriately can refine the grain size, improve the strength and toughness of CVD deposited films, enhance the adhesion between deposited films and substrates, and make deposited films have strong directionality.
Due to the advantages of UWCVD that cannot be obtained by some other CVD methods, such as fine and dense deposited film structure, strong adhesion between deposited film and substrate, and good strength and toughness of deposited film, it is necessary to explore and study this new process, and it is also possible to effectively apply it to industrial production.
Application
1. Protective coating
Materials used in many special environments often require coating protection to provide functions such as wear resistance, corrosion resistance, high temperature oxidation resistance, and radiation resistance. TiN, TiC, Ti (C, N) and other thin films prepared by CVD method have high hardness and wear resistance. Coating only 1-3 μ m TiN film on the cutting surface of the tool can increase its service life by more than three times. And other metal oxides, carbides, nitrides, silicides, phosphides, cubic boron nitride, diamond-like carbon films, as well as various composite films, also exhibit excellent wear resistance. In addition, the corrosion resistance of Al2O3, TiN and other thin films obtained through deposition is very good, while the corrosion resistance of amorphous films containing chromium is even higher. Silicon based compounds such as SiC, Si3N4, MoSi2, etc. are important high-temperature oxidation resistant coatings, which generate dense SiO2 films on the surface and can withstand oxidation at 1400-1600 ℃.
2. Microelectronics technology
In the basic manufacturing process of semiconductor devices and integrated circuits, the core steps include epitaxial growth of semiconductor films, formation of p-n junction diffusion elements, dielectric isolation, deposition of diffusion masks and metal films. Chemical vapor deposition has gradually replaced old processes such as high-temperature oxidation and diffusion of silicon in the preparation of these material layers, and occupies a dominant position in modern microelectronics technology. In the production of ultra large scale integrated circuits, chemical vapor deposition can be used to deposit polycrystalline silicon films, tungsten films, aluminum films, metal silicides, silicon oxide films, and silicon nitride films. These thin film materials can be used as gate electrodes, interlayer insulation films for multi-layer wiring, metal wiring, resistors, and heat dissipation materials.
3. Superconducting technology
CVD preparation of superconducting materials was invented by Radio Corporation of America (RCA) in the 1960s. The Nb3Sn low-temperature superconducting tape produced by chemical vapor deposition has a dense coating, easy thickness control, and good mechanical properties. It is currently the best material for firing high field strength small magnets.
4. Solar energy utilization
Solar energy is an inexhaustible source of energy, and utilizing the photoelectric conversion function of inorganic materials to make solar cells is an important way to harness solar energy. At present, CVD technology, including LPCVD and PCVD processes, is commonly used to prepare polycrystalline silicon thin film batteries. The successful trial production of silicon and gallium arsenide homojunction cells, as well as various heterojunction solar cells made from II-V and I-VI semiconductors, such as SiO2/Si, GaAs/GaAlAs, CdTe/CdS, etc., are almost all made in thin film form, and vapor deposition is their main preparation technology.
5. Production of Whiskers
Whiskers are a type of developing single crystal that plays a significant role in the field of composite materials and can be used to produce some new types of composite materials. The chemical vapor deposition method uses the hydrogen reduction properties of metal halides in the production of crystal whiskers. Chemical vapor deposition can not only prepare various metal whiskers, but also produce compound whiskers such as alumina, diamond, titanium carbide whiskers, and so on.
6. Preparation of Precious Metal Thin Films
Precious metal thin films have attracted the interest of researchers due to their excellent oxidation resistance, high conductivity, strong catalytic activity, and extremely stability. Compared with other methods of generating precious metal thin films, chemical vapor deposition has more technical advantages, so most methods of preparing precious metal thin films use this method. The types of deposition materials used for depositing precious metal thin films are relatively wide, but most of them are halides and organic compounds of precious metal elements, such as Cl3Ir, COCl2, platinum chloride, iridium chloride, DCPD compounds, C5H2F6O2 or C5H5F3O2 compounds, C15H21IrO6 and C10H14O4Pt, etc.
