Synthesis of copolymer films by RF plasma: Correlation between plasma chemistry and film characteristics

Plasma copolymerization has the ability to design new functional thin films. Combinations of the different monomers were used to deposit copolymer thin films on a silicon substrate by radio-frequency pulsed inductively coupled plasma. In order to gain an insight into the plasma copolymerization process, the plasma was investigated by means of the optical emission spectroscopy for different reactive compositions. The physical chemistry of the deposited copolymer films was analyzed by several surface analytical techniques such as X-ray photoelectron spectroscopy (XPS) or time-of-flight secondary-ion mass spectrometry (ToF-SIMS). Information from the plasma and the deposited films was correlated and provides some possible steps for organic plasma-chemical conversion into a stable polymer. In our paper, optical emission spectra of the plasma and XPS spectra of the films are predictive; plasma emitting a higher relative benzyl radical signal results in the deposition of a more aromatic plasma-deposited polymer films, and thin polymeric films with desired functionalities can be therefore deposited by an appropriate selection of the comonomers.