Plasma Enhanced Deposition
One of the required techniques to perform deposition in lasers technology is the PECVD Coating system, which is used often for oxides and nitrides deposition. Coating is done in a reactor with a temperature of about 400 ° C, and generated plasma increases the required energy for the reaction (even in a temperature of 250 - 400degrees with small amounts), to the desired extent.
In this system, compared to the traditional mode, is added a plasma source to system. One another major advantage of this method than conventional methods is the reduction in deposition temperature, whereas by supporting energy, which is derived from plasma and is entered to gas molecules, compensate the lack of kinetic energy.
As indicated in Figure 1, the main difference is adding one radio-frequency generator to generate the plasma.
Right. standard Coating system, Left. vertical single-wafer PECVD system.
Sometimes it is possible that use of two plasma source in CVD system. Using two plasma sources causes to the density of plasma and energy of ion be adjusted independently. For example, the 13.56 MHz converter, the density of plasma, and low 350 kHz frequency converter indicate the energy of ions. As shown in Figure 2, PECVD systems can have a horizontal structure.
Figure 2: Schematic view of a horizontal PECVD system
The properties of deposited oxides and silicon nitride by this method is completely different with obtained result from LPCVD method, which is done at higher temperatures. These properties are including Surface hardness and stoichiometry, that as a result, lead to changes in surface smoothness, dielectric constant, and refractive index, and so on.
In Table 1, is shown most common chemical needed reactions to build some of the chemical and physical layers. In Table 1, is given different conditions for coating the layers. In this table, is brought required gases to form a layer, the type of system, chemical coating, the type of composition, and required temperature.
Table 1: The conditions of coating to form a common layers.
