Vapor Deposition Precursors

Vapor deposition can be classified into chemical and physical vapor deposition using physical process or chemical reaction that happen in the gas state to form functional or decorative films on the surface of the workpiece. In the chemical vapor deposition process, under the function of chemical reaction and using one or more compounds containing film elements as the precursors, a thin film can be obtained and endow the surface some special properties. In physical vapor deposition process, the solid or liquid surface is vaporized into gaseous atoms, molecules or partially ionized into ions. Then, under vacuum conditions, by means of low-pressure gas or plasma process, thin films with a specific function are deposited on the substrate surface. As the raw material, vapor deposition precursors play an irreplaceable role in the process of vapor deposition and largely determine the performance of the final product. Therefore, understanding the nature of vapor deposition precursors and making a reasonable choice are necessary.

Figure 1. Schematic diagram of a basic physical vapor deposition system.

Applications:

• Protective coating field: By coating to make some materials have high wear resistance, high temperature oxidation and radiation resistance that are the basic requirements for material applied in special environments. TiN films can be used to extend the service life of cutters, which is prepared by vapor deposition method. In addition, the vapor deposition coating of Mo and W with excellent high temperature and corrosion resistance are generally applied in turbine blades, nozzles of rocket engines and other equipment parts.

Figure 2. An example of vapor deposition coating.

• Microelectronics field: In the production of large-scale integrated circuits, vapor deposition can be used to deposit polysilicon films, tungsten films, aluminum films, metal silicides, silicon oxide films, silicon nitride films, etc. These film materials can be used as gate electrodes, metal wiring and the others. Moreover, vapor deposition has gradually replaced the traditional processes and has taken a dominant position in modern microelectronics technology.
• Solar cell field: Solar energy is an inexhaustible energy source and making polysilicon thin film cells is an important utilization method. Manufacturing polysilicon thin film cells, including homojunction cell and heterojunction solar cell, mainly uses vapor deposition technology.

Figure 3. Perovskite thin film obtained by vapor deposition.

• The others: Vapor deposition is also widely applied in the fields of architecture, electricity and medicine. For example, golden TiN is especially popular in the decoration industry. In addition, hydroxyapatite film is prepared by vapor deposition technology, which has good biocompatibility and is widely used in dental implants and artificial bones.

Classification:

According to the applied preparation techniques, vapor deposition precursors can be divided into physical vapor deposition precursors and chemical vapor deposition precursors

• Physical vapor deposition precursors: Physical vapor deposition precursors mainly include Cd, Co, Cr, Ti Zn, etc.
• Chemical vapor deposition precursors: According to the metal element, chemical vapor deposition precursors can be classified into many groups, such as ytterbium titanium, aluminum magnesium and the others.

Figure 4. Examples of chemical vapor deposition precursors.

References:

1. Wang, Ying, Chen, Weijin, Wang, Biao, Zheng, Yue. Ultrathin Ferroelectric Films: Growth, Characterization, Physics and Applications[J].Materials,2014,7(9):6377-6485.
2. Bhachu D S, Scanlon D O, Saban E J, et al. Scalable route to CH₃NH₃PbI₃ perovskite thin films by aerosol assisted chemical vapour deposition[J]. Journal of Materials Chemistry A, 2015, 3.