Imprinting of nanopores in organosilicate dielectric thin films with hyperbranched ketalized polyglycidol

Hyperbranched polyglycidol (PG) was synthesized via a new polymerization pathway of glycidol using zinc glutarate (ZnGA) as a catalyst. ZnGA was found to be a highly active catalyst for the ring-opening polymerization of glycidol. The complex chemical structures of hyperbranched PG and its ketalized derivative (K-PG) were determined by specialized 13C nuclear magnetic resonance spectroscopic techniques. In addition, a new soluble silsesquioxane copolymer, poly(methylsilsequioxane-co-1,4-bis(ethylsilsesquioxane)benzene), i.e. a PMSSQ-BESSQB precursor, was synthesized via the sol-gel reaction of its monomers. The precursor solution was found to produce good quality thin films. K-PG was found to have good solubility in common solvents and good miscibility with the PMSSQ-BESSQB precursor. Moreover, K-PG was found to exhibit a sacrificial thermal decomposition characteristic that makes it suitable for use as a porogen in the fabrication of porous PMSSQ-BESSQB dielectric films. K-PG can be loaded into the PMSSQ-BESSQB precursor at concentrations up to 40 wt%. Synchrotron grazing incident small-angle X-ray scattering studies of the porous thin films prepared from PMSSQ-BESSQB/K-PG composite films with various compositions found that the average size of pores in the porous dielectric films varies from 6.7 to 18.5 nm as the initial loading of the K-PG porogen is increased from 10 to 40 wt%. These pores are spherical and have a sharp interface with the dielectric matrix. The porosities P of the porous PMSSQ-BESSQB films were found to increase almost linearly from 0 to 37 vol% as the initial loading of the K-PG porogen was increased up to 40 wt%. The presence of the imprinted pores reduced the refractive index n and dielectric constant kvalues of the PMSSQ-BESSQB films almost linearly as the initial loading of the K-PG porogen was increased. These results lead to the conclusions that the sacrificial thermal decomposition of the K-PG porogen molecules successfully imprints nanopores into the PMSSQ-BESSQB dielectric films and that the population of the imprinted pores increases proportionally with increases in the initial loading of the porogen, up to concentrations of 40 wt%. The pore structures and properties of the nanoporous PMSSQ-BESSQB films imprinted by the K-PG porogen indicate that they are good candidates for use as interdielectric materials in the fabrication of advanced microelectronic devices.