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CVD Precursors

The process of heating, plasma excitation, or optical radiation to make gaseous or vaporous chemical substances react and deposit on the substrate in an atomic state, thereby forming the required solid film or coating is called chemical vapor deposition (CVD). CVD precursor refers to a gaseous reactant or a volatile liquid reactant that constitutes a thin film element used in the chemical vapor deposition process. The CVD precursor is a key material used in the CVD process, and its chemical structure determines the film properties during the deposition process.

Applications:

Due to the advantages of rich variety and easy preparation, CVD precursors have very important applications in the fields of metal thin films and ceramic thin films.

High-k oxide film: High-k oxide film with high dielectric properties is one of the important microelectronic materials. Chemical vapor deposition (CVD) is the preferred method for preparing high-k oxide thin films due to its excellent compatibility with semiconductor processes. For the vapor deposition of Group IVB metal oxides, commonly used metal precursors are mainly metal alkoxides, β-diketone salts or chlorides, which have certain advantages. However, the precursor contains elements such as C, H or Cl, so it is easy to remain in the prepared film and deteriorate the film performance. The anhydrous nitrates of Ti, Zr and Hf have good volatility, and can be used as a new type of carbon-free inorganic precursors to deposit oxide films such as TiO₂, ZrO₂ and HfO₂. In addition, since the nitrate group contains only N and O elements, contamination of elements such as C, H and Cl is avoided. At the same time, nitrate can only rely on its own decomposition to form a film without introducing oxidizing reactive gases, which avoids the pre-reaction of these oxidizing gases with the Si substrate to form a low dielectric constant interface layer. The aforementioned characteristics make the anhydrous metal nitrate CVD precursors very important applications in the preparation of high-k oxide thin films.
Coating material: Chemical vapor deposition is a widely used process for preparing silicon carbide (SiC) ceramic coatings and high-temperature silicon carbide ceramic matrix composite materials, which can be used for fine control of multiple parameters (temperature, pressure, residence time, etc.). The CVD process can achieve the near-net shape of the SiC coating or the substrate, and can accurately adjust the parameterization of the deposition rate and microstructure. Trichloromethylsilane (CH₃SiCl₃, abbreviated as MTS) and hydrogen (H₂) precursor system is a CVD precursor widely used in the CVD process of SiC materials. MTS can decompose the stable SiCl_x component, and the chloride ion in this component prevents the formation of silicon-containing droplets to a certain extent. H₂ can promote the removal of the Cl element in SiCl_x component, and can inhibit the removal of H element in the CH_x component, which limits the rapid formation of C at high temperature. Therefore, MTS+H₂ as a CVD precursor system has the advantage of easy operation and control. The MTS+H₂ precursor system can control the growth characteristics of SiC through the adjustment of deposition parameters and facilitate the generation of stoichiometric SiC. The SiC coating material made with MTS+H₂as the CVD precursor has the advantages of excellent performance and stable properties, and has been applied in many fields.

CVD Precursors Figure 1. Morphology of SiC ceramic deposited by MTS+H₂ as CVD precursor

Integrated circuits: Silicon-based precursors are widely used in the field of integrated circuits, and can be used to manufacture barrier layers, insulating layers, and filling layers. Silicon-based chemical vapor deposition (CVD) process is a thin film manufacturing process widely used in the manufacture of integrated circuits. The silicon-based precursors used in the silicon-based chemical vapor deposition process generally include haloalkyl precursors and amine-based precursors. In the early days, haloalkyl precursors were widely used CVD precursor materials. They have the characteristics of deposition rate and simple manufacturing process, but they have the problems of high toxicity, sensitivity to air, flammability and explosion, and high risk. The amine precursor is a CVD precursor formed by replacing the chlorine-containing group with an amine group. This kind of precursor can avoid the problems caused by elemental chlorine, and it has various types, which brings unlimited possibilities for the manufacture of devices required for integrated circuits. At present, the amine precursors that have been developed and used mainly include tris(dimethylamino)silane, dimethyl bis(dimethylamino)silane, hexamethyldisilazane, bis(dimethylamino) silane, etc.

CVD Precursors Figure 2. Tris (dimethylamino) silane CVD precursor used in integrated circuits

References:

Fainer I N. (2013). "Synthesis of Silicon Carbonitride Dielectric Films with Improved Optical and Mechanical Properties from Tetramethyldisilazane." Glass Phys Chem 39(1), 77-88
EVANS A G. (2010). "Perspective on the development of high-toughness ceramics." Journal of the American Ceramic Society 73(2), 187-206.
MOTOJIMA S. (1990), "Chemical vapor deposition of SiC layers from a gas mixture of CH3SiCl3+H2 (+Ar), and effects of the linear velocity and Ar addition." Journal of Vacuum Science & Technology A Vacuum Surfaces & Films 8(5), 3763-3768.

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