Topological Design of Low Dielectric Ladder-like Polysilsesquioxane and Copolymers

Abstract

Low dielectric constant (low-k) materials are critical for advanced packaging in high-density microelectronic devices and high-frequency communication technologies. Ladder polysiloxanes, which are characterized by their unique double-chain structure and intrinsic microporosity, offer remarkable advantages in terms of thermal stability, oxidation resistance, and dielectric performance. However, structural defects in ladder polysiloxanes, such as cage-like and irregular oligomers, and their effects on dielectric properties remain underexplored. In this study, a series of ladder-like polysiloxanes (X-TMS) with diverse side groups weresynthesized via a one-step base-catalyzed method. The influence of the benzocyclobutene (BCB) side groups on the formation of regular ladder structures was systematically investigated. Notably, BCB incorporation disrupted the structural regularity, favoring the formation of cage-like and irregular topologies, which were extensively characterized using ²⁹silicon nuclear magnetic resonance spectroscopy (²⁹Si-NMR), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and X-ray diffraction (XRD). These structural defects were beneficial for improving the hydrophobicity and thermal stability. Copolymerization of X-TMS with commercial DVS-BCB resins further enhanced the mechanical properties, with the elastic modulus increasing from 3.6 GPa to 4.4 GPa and water absorption reduced from 0.33 wt% to 0.06 wt%. This study establishes a clear correlation between topological structures and material properties. These findings not only advance the understanding of the structure-property relationships in ladder polysiloxanes but also provide a novel approach for designing high-performance interlayer dielectric materials for next-generation microelectronics.