CVD can be defined as forming a solid thin film atomic or molecular deposition on a heated surface, with the solid originating from a chemical reaction where the precursors are in the vapour phase. Deposited species are atoms or molecules or combination thereof. PACVD process occurs at lower temperatures than the conventional process of CVD, because the plasma and thermal energy is used to initiate the reaction. CVD process is distinguished from the PVD process that all the materials which cause the film are in the gas phase, while in the PVD at least one of them is solid phase (usually a metal).