The monomer inlet position effect on the fluorocarbon film deposited using RF plasma

The octafluorotoluene (C7F8) monomer was used to deposit fluorocarbon (a-C:F) film with an aromatic ring structure in an RF plasma reactor. While keeping the argon gas inlet position fixed, the inlet position effect of the C7F8 monomer on the deposited a-C:F film characteristics was investigated. It was found that, when C7F8 entered upstream of the plasma, the deposited film possessed no aromatic structure and the F/C atomic ratio of the film was higher than 1.4. Whereas for film deposited as C7F8 entered from the afterglow region (the so-called 'downstream' process), copious amount of the aromatic structure were preserved and the F/C ratio of the film was lower than 1.0. Higher deposition rate and rougher surface were also found in films deposited in the downstream process. A simplified reaction mechanism is proposed based on these results.