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

Abstract

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.