Pulsed Plasma Synthesis of Low Dielectric Constant Materials

ABSTRACTThe utility of a variable duty cycle, pulsed plasma polymerization technique to produce low dielectric constant materials (k < 2.3) is described. The molecular compositions (and thus the dielectric constants) of the plasma polymers are controllable via changes in the plasma duty cycles employed during synthesis, all other reaction variables being held constant. In the present study, this compositional controllability under pulsed conditions is illustrated with two fluoroaromatic monomers. The dielectric constants of the films decrease as the plasma duty cycles employed during polymerization are decreased. Although the as deposited films exhibit relatively poor thermal stability, it was discovered that post-plasma annealing of the films, particularly at 400 °C under N2, provides dramatic improvements in the thermal stability of these materials. Most importantly, this enhanced thermal stability is achieved with relatively minor changes in the dielectric properties of these materials. In fact, synthesis of high thermal stability films having k < 2.0 is demonstrated in this work using the perfluoroaromatic monomer perfluoroallyl benzene.