Molecular structure of a random copolymer film by plasma-enhanced CVD from a mixture of cyclohexa hydrocarbons

An important issue in the polymerization of a polymer film by plasma‐enhanced chemical vapor deposition (PECVD) is how to control the polymer structure. As is generally recognized, it is extremely difficult to control the process because it is very complex. For example, various precursors in the plasma arise from fragmentation of source monomers, which can easily change by varying the plasma conditions. High‐energy electrons and ions in the plasma bombard the surface of the deposited film and affect the chemical reaction on the film. Moreover, the droplets that arise from the reactor wall by sputtering will accumulate on the film. However, if we aim to fabricate only a photonically functional polymer film, we will be able to find a solution. In this paper, we propose copolymerization from two types of monomers; one type is used as jointing materials by cracking, and the other is used as a photonic functional segment without serious deformation. This difference of action arises from a difference in the formation enthalpy. To confirm this idea, as an initial step, we copolymerized a film from a mixture of benzene (C6H6) as the functional segment and cyclohexene (C6H10) as the jointing material under the low radio frequency power. The deposited film consists of sp2 bonding clusters surrounded by sp3 bonded (alkyl) networks. We confirmed that the sp2 bonding clusters mostly belong to phenyl, with a few belonging to olefins arising from decomposed C6H6. In addition, the amount of sp2 bonding increases proportionally with increasing ratio of C6H6 in the mixture, and the ratio of phenyl in the film becomes comparable to that of polystyrene. From these facts, we speculate that C6H10 acts as the jointing material and C6H6 as the functional segment. Additionally, we introduced tetrafluorocarbon (CF4) to the plasma. CF4 decomposes with a smaller energy than C6H10, and it forms mainly fluorine and CF3 radicals. The fluorine radical pulls out hydrogen from the film and reacts to form dangling bonds in the film. Moreover, we speculate that they will terminate the dangling bonds. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.