Monday, November 5, 2007

Crystallization of Zeolitic-Amorphous Silica in Nanoporous Mel Zeolite Films

Yan Liu1, Christopher M. Lew1, Minwei Sun1, Junlan Wang2, and Yushan Yan1. (1) Department of Chemical & Environmental Engineering, University of California, Riverside, 900 University Ave., Riverside, CA 92521, (2) Mechanical Engineering, University of California, Riverside, Bourns Hall A242, Riverside, CA 92521

Nowadays, low-dielectric-constant (low k) materials to reduce signal delays and crosstalk noise between the metal interconnects within integrated circuits are critically needed for the semiconductor devices. Pure-silica-zeolite is a good candidate for low-k material due to its intrinsically uniform pore size and distribution, high hydrophobicity, strong mechanical strength and chemical stability. In our previous work, spin-on MEL zeolite nanocomposite thin films consisting of crystalline zeolites and zeolitic-amorphous silicas have been demonstrated to have superior mechanical and dielectric performance. While the MEL zeolite crystals give the material the low-k value due to their crystalline and porous framework, the role of the zeolitic-amorphous silica in the nanocomposite is not well understood. In this study, zeolitic-amorphous silica was separated from the MEL zeolite suspension and compared with non-zeolitic-amorphous silica. Detailed parametric study is performed on spin-on zeolitic-amorphous silica films, non-zeolitic-amorphous silica films, the blending of zeolite crystal and zeolitic-amorphous silica films, and the blending of variable amount ratio of zeolite crystal to non-zeolitic-amorphous silica films. The reduced elastic modulus and hardness of the films were measured with nano-indentation. And the crystallinity of the films was studied using X-ray diffraction (XRD) and high resolution transmission electron microscopy (TEM). The mechanical property and crystallinity results reveal that zeolitic-amorphous silica has a nanoporous quasi-crystalline structure, which is different from the dense non-zeolitic-amorphous silica. Since comparing with zeolite suspension, zeolitic-amorphous silica can yield smoother film with tunable crystallinity and mechanical strength via spin coating, our finding might open a new and promising route for preparing zeolite low-k materials.