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Author: Ali Kosari Mehr
Developed in part to increase the efficiency of chemical reactions in lower temperatures, plasma-enhanced chemical vapor deposition (PECVD) or plasma-assisted chemical vapor deposition (PACVD) is one of the modified CVD processes. In PECVD systems, through either diode glow-discharge electrodes or an induction coil positioned outside of the chamber, the electric power required for the generation of the plasma can be supplied. Often operating in working pressures ranging between 10 to 100 Pa, PECVD systems include plasma in which the ionization degree is generally just 10-4, hence resulting in the gas in the reactor being mainly comprised of neutrals. Obtaining energy from the electric field present in the plasma, electrons and ions constantly move in the chamber. With the mean electron energy ranging between 2 and 8 eV, electrons in the plasma possess temperatures ranging from 23000 to 92800 K. Nonetheless, heavy, fairly immobile ions in the plasma could not obtain sufficient coupling energy from the electric field, causing them to have marginally higher energy compared to neutrals at room temperature. Therefore, mainly, the ion temperature in the plasma is approximately 500 K.
In PECVD processes, thermal equilibrium is not sustained between electrons and neutrals owing to the extremely higher temperature of electrons compared to the temperature of the gas. Thus, the glow discharge could be regarded as cold plasma in which there are high-temperature electrons/hot electrons and gas molecules being at room temperature. Having accommodated the facts mentioned, one can affirm that these hot electrons enhance the chemical reactions in the plasma, culminating in the decreased temperature required for reactions.
So far, various advancements have been offered to develop PECVD processes. Illustrating these advancements, one can refer to microwave-based plasmas utilized to decrease the working pressure. Moreover, a magnetic field can be added to the system to create an electron cyclotron resonance (ECR) condition (i.e., a resonance between the applied electric field and the electron cyclotron frequency) [2,1].
References:
1. Chow LA (2012) Equipment and Manufacturability Issues in CVD Processes. In: Handbook of Thin Film Deposition: Techniques, Processes, and Technologies: Third Edition. Elsevier Inc., pp 127–178. Webpage
2. Wasa K, Kitabatake M, Adachi H (2004) Thin Films Material Technology: Sputtering of Compound Materials. Springer. Webpage
