Dielectric anisotropy and molecular orientation of fluorinated polymers confined in submicron trenches

Dielectric anisotropy of polymers with low dielectric constant is an import ant property to consider for developing interlevel dielectrics for advanced on-chip interconnects. The effect of molecular structure on dielectric ani sotropy has been Investigated for two low dielectric-constant polymers: a f luorinated polyimide, FPI-136M and a fluorinated poly(aryl ether), FLARE-1. 51, Optical and electrical measurements have been carried out to determine the dielectric anisotropy in blanket thin films and trench line structures. Results from optical measurements show that the FPI-136M film has a larger birefringence than the FLARE-1.51 film, indicating a larger dielectric ani sotropy; This reflects a higher degree of in-plane molecular orientation fo r the rigid rod-like: fluorinated, polyimide, while the fluorinated poly(ar yl ether) has an ether linkage that allows greater chain flexibility. Elect rical measurement of the dielectric anisotropy has been performed using a m etal-insulator-metal structure to determine the out-of-plane dielectric con stant and an interdigitated submicron metal line structure coupled with a t wo-dimension computer model to determine the in-plane dielectric constant. Results show that the rigid rod-like FPI-136M has a smaller dielectric anis otropy compared with that measured from the optical birefringence. In contr ast, the dielectric anisotropy of the more flexible FLARE-151 is found to b e similar to that obtained from the optical birefringence measurement. Four ier transform infrared (FTIR) spectroscopy has been used to examine the mol ecular structures in the blanket films and the trench line structures. The FTIR spectra of FPI-136M show that its molecular structure in submicron tre nches is significantly different to that in spin-coated blanket film. This is in contrast to FLARE-1.51, which has similar molecular orientation for t he blanket film and the trench structure. Thus, the molecular orientation o f the rigid rod-like FPI-136M seems to be more affected by the confinement in submicron trenches, giving rise to a lesser degree of dielectric anisotr opy than that observed in blanket films. (C) 2000 American Vacuum Society. [S0734-211X(00)08801-6].