(100i) Benzocyclobutene Functionalized Polynorbornes: Directly Photopatternable Dielectrics

Polynorbornene (PNB) polymer systems containing benzocyclobutene (BCB) have been developed for application as directly photopatternable, ultra low-k dielectrics.  Random copolymers of BCB functionalized norbornene along with non-functionalized norborne were created via ring opening metatheis polymerization (ROMP). Optical patterning of thin polymer films was achieved through photo-mediated crosslinking of BCB moieties. Thermal curing and etching after crosslinking yielded negative tone dielectric material. Coefficient of thermal expansion (CTE), dielectric constant (k), and water absorption were tested and found to be within current process windows for microelectronics packaging. The effect of varying ratios in the copolymer of BCB functionalized to non-functionalized monomers was studied. A sharp change in relevant properties was observed consistently around 25% BCB monomer loading, suggesting a lower limit for useful materials. Also studied was the effect of multiple fused rings in the monomer backbone using analogs of tetracyclododecene (TCD). TCD polymer systems were discovered to have high glass transition temperatures (Tg) than their single ring PNB counterparts: 150 ˚C for TCD vs. 120 ˚C for PNB. Glass transitions for copolymers of TCD and PNB were found to vary linearly between the two homopolymer temperatures, showing the potential for a designer dielectric material with highly adjustable characteristics.