Plasma enhanced chemical vapor deposition

Marek Eliáš

Plasma enhanced chemical vapor deposition (PECVD) is a method for the creation of thin films with thicknesses of few tens of nanometers up to several micrometers. It belongs to CVD techniques that utilize reactants in the form of gases and vapors. In thermal CVD, the energetic threshold of chemical reactions is overcome by heating the reactants, i.e. by heating the CVD reactor or the substrate. Unlike in CVD, the reactions in PECVD systems can proceed at low temperature because the reactants are activated by plasma. Plasma contains electrons and ions possesing energies that are able to break chemical bonds. Therefore, electron-molecule collisions create radicals in the gas phase and ions bombarding the surface of growing film activate the surface by creation of dangling bonds. The ions also help to densify the growing film by etching a weakly bonded terminating groups.

The PlasmaPro 100 PECVD system utilizes inductively coupled plasma (ICP) placed on the top of the reaction chamber for the activation of gas mixture. The RF bias (a weak capacitively coupled discharge) can be applied at the substrate electrode in order to increase the energy of incoming ions. The Si-based materials can be deposited either from silane (SiH4) or vapors of tetraethyl silicate (TEOS). Amorphous hydrogenated silicon (a-Si:H) films can be obtained from the mixture of SiH4/H2. Silicon oxide films are obtained by mixing SiH4 or TEOS (C8H20O4Si) with N2O whereas silicon nitride films require N2 instead of N2O.