The pore structure and its impacts on property and performance of a spin-on porous low K dielectric

A methylsilsesquioxane based porous spin-on dielectric has been evaluated at International SEMETCH (ISMT) for advanced interconnect applications. The pore structures and their impacts on the properties and CMP performance of the dielectric films have been studied. The pore structures have been characterized with various techniques including transmission electron microscopy (TEM), positron annihilation lifetime spectroscopy (PALS), small-angle neutron scattering (SANS) and specular X-ray reflectivity (SXR). The periodic tubular pore structures observed in the films played an important role in improving overall mechanical property. However, this type of film failed in CMP process via cohesive fracture; the layered structure near film boundaries is the main culprit for the failures as layered structures are likely to exhibit low cohesive strength. The film might have improved cohesive strength withstanding for the CMP process if one can make the pore structure more randomly orientated throughout the entire film thickness. Minimizing pore tube lengths could be an effective way to avoid layered structures and improve mechanical integrity of the porous low k films.