MECHANISMS OF PLASMA POLYMERIZATION OF VARIOUS SILICO-ORGANIC MONOMERS

The plasma polymerization of hexamethyl disiloxane (HMDSO), divinyltetramethyl disiloxane (DVTMDSO), and octamethyl cyclotetrasiloxane (OMCATS) was investigated using either argon or argon/oxygen mixtures as reactants. With argon, different mechanisms of polymerization for each polymer were identified reflecting its respective nature. For HMDSO, formation of Si-CH2-Si bonds plays a decisive role, whereas in DVTMDSO Si-(CH2)(4)-Si bridges are formed. In both cases a second mechanism exists leading to the loss of SiCxHy groups. Finally, OMCATS polymerizes via the formation of polymethylsiloxane chains and rings. These various mechanisms result in differences in the properties of the polymer films. In contrast, almost inorganic films were obtained with oxygen irrespective of the monomer. An investigation of the deposition kinetics shows that the plasma power and the monomer evaporation temperature are the decisive parameters determining the polymer growth rates. A comparison of direct and remote plasma reaction reveals that in the cases of HMDSO and OMCATS direct plasma dissociation is necessary to promote the polymerization process, whereas DVTMDSO also polymerizes under remote conditions.