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  • Principle of Chemical Vapor Deposition (CVD)

    Chemical vapor deposition (CVD) is a well-known technology in the field of nano manufacturing, which is often used in large-scale integrated circuits, insulating materials, magnetic materials, optoelectronic materials. Chemical vapor deposition (CVD) can deposit evaporated reactants on the surface to form thin films, for example, graphene is the most widely recognized product of CVD. So, what is the principle of CVD?
     

     
    Principle of Chemical Vapor Deposition (CVD) 
    CVD has been studied since the end of the 19th century. It is mainly used in the synthesis and preparation of important materials. If we want to know how CVD makes a specific film, we must first understand its principle.
     
    CVD belongs to the "bottom-up" nano manufacturing technology. Its principle is to introduce the vapor of gaseous or liquid reactant containing film elements and other gases needed for the reaction into the reaction chamber. By increasing the temperature, plasma action, light radiation or other forms of energy, CVD can produce chemical reactions on the substrate surface and generate new solid substances to be deposited on the surface.
     

    Schematic diagram of CVD method
    CVD consists of four main stages:
    ① The reaction gas diffuses to the surface of the material;
    ② The reaction gas is adsorbed on the surface of the material;
    ③ Chemical reaction occurs on the surface of the material;
    ④ The gaseous by-products are separated from the material surface.
     
    Because of the molecular level nucleation or growth, CVD is more suitable for the formation of dense and uniform films on the irregular substrate surface. CVD deposition speed is fast and film quality is stable. Some special films also have excellent optical, thermal and electrical properties, so it is easy to achieve mass production.
     
    The deposition temperature of CVD is usually very high, between 900 ℃ ~ 2000 ℃, it is easy to cause the deformation of parts and the change of structure, so as to reduce the mechanical properties of the body material and weaken the binding force between the body material and the coating, which limits the selection of substrate, the deposition layer or the quality of the workpiece. Therefore, low temperature and high vacuum are the main development direction of CVD.
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