Plasma Enhance Chemical Vapor Deposition

Plasma Enhanced Chemical Vapour Deposition (PECVD) is a process in which thin films of different materials are deposited on a substrate surface at low temperatures. Since plasma can reduce the activation energy of a reaction, the deposition temperature can be significantly decreased. The presence of energetic particles (ions, electrons, etc.) and continuous bombardment of the metallic surface by these particles makes a suitable condition for occurrence of chemical reactions and creation of coatings at low temperatures. Moreover, surface bombardment by energetic particles removes the surface oxide layers and as a result modifies the physical, chemical and mechanical properties of the coating. Thus, in comparison with the common CVD process, in PACVD the chemical reactions, which lead to the formation of coating, happen at lower temperatures.
Plasma is generated by injection of a reactant gas in a space between two parallel electrodes, one of two electrodes is connected to the radio-frequency (RF) power supply and the other one is grounded. By applying an RF potential, plasma is generated; High-energy electrons in the plasma, ionize the reactant gas and generate more chemically reactive radicals. These radicals react to deposit a thin film on the substrate surface. The substrate temperature, which is placed on the ground electrode, can be varied from room temperature to 250 °C. The type of deposition determines the system temperature. The basic principles of plasma deposition are similar to plasma etching; the only difference is that in the former a thin layer is deposited on a substrate surface while in the latter a layer is removed from a substrate surface.
In this process, the samples are first subjected to a surface cleaning in an inert gas plasma medium like argon and their temperature increases to the desired value. Then gaseous reactants, a mixture of nitrogen, hydrogen, argon and TiCl4 gases with certain ratios, are sent into the chamber; finally the deposition process is performed by controlling parameters such as temperature, time, pressure, frequency and pulse width. Using this method makes it possible to fabricate single- or multilayers binary, ternary and quaternary coatings such as TiN, TiC, CNTi, TiAlN, TiBN and TiAlCN. One of the advantages of this method is the ability to perform nitration process and consequently deposition process, which leads to the formation of hard coatings. What’s more, this method has a higher deposition rate compared with the other methods, while maintaining the deposition quality.