Nanopore Formation in a Polyphenylene Low-kDielectric

Nanometer-scale porosity is being introduced into low- k dielectrics in an attempt to achieve inter-level metal insulators with permittivities less than 2.0. It has proven extremely difficult to describe pore formation and to characterize the porous structure. This work investigates pore formation in a polyphenylene low- k dielectric based on pyrolysis of a porogen (27 vol %) in a polyphenylene matrix. One unique aspect presented here is the characterization of the nanoscale structure at various stages of pore formation through the use of a deuterated porogen. The combination of X-ray reflectivity (XRR) and small-angle neutron scattering (SANS) is found to be a powerful technique for describing porogen degradation and pore formation in nanoporous materials. The average radius of the porogen domains was approximately 60 Å with a relatively broad size distribution. During degradation the smaller porogen domains collapse, while the larger domains yield stable pores. This collapse of the relatively large number of smaller domains results in a significant reduction in film thickness, a porosity that is significantly smaller than the porogen content, a pore size distribution that is narrower than the porogen domain size distribution, and an average pore size of approximately 80 Å.