Surface analysis of fluorine-containing thin films fabricated by various plasma polymerization methods

Plasma-polymerized fluorine-containing thin films were fabricated by five different plasma methods, viz. inductively coupled plasma (ICP), pulsed-plasma (PP), capacitively coupled plasma (CCP), self-ignition plasma (SIP), and plasma source ion implantation/inductively coupled plasma (PSII/ICP). Octafluoropropane (C3F8) was mixed with acetylene (C2H2) to investigate the effect of different plasma techniques on the films. The properties of the plasma polymers, viz. hydrophobic properties, binding structure, deposition rate, and chemical composition, varied considerably depending on the plasma polymerization method. The plasma-polymerized thin films made by the different methods were characterized using surface analytical instruments: field-emission scanning electron microscope (FE-SEM), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Cross-section images from FE-SEM revealed that the deposition rate of the polymer film in the case of using CCP plasma was higher while that for PSII/ICP and self-ignition plasma, respectively, was lower compared with the deposition rate of the ICP and pulsed-plasma. The water contact angle measurement showed that the ICP and PSII/ICP techniques produced more hydrophobic surfaces. XPS and TOF-SIMS analyses indicated that the ICP and PSII/ICP methods produced more F-containing functional groups, especially CF2 and CF3 groups. Also, the NEXAFS results revealed that the ICP and PSII/ICP techniques provide more fluorine species on the plasma polymer surface compared with other techniques.