Porous Methylsilsesquioxane for Low-k Dielectric Applications

Abstract

A commercially available spin-on glass ͑methylsilsesquioxane, MSQ͒ was modified by the introduction of porosity. The porosity reduced the effective dielectric constant of the MSQ by the incorporation of air. The pores were created by adding a sacrificial polymer ͑substituted norbornene polymer͒ to the silsesquioxane matrix. The sacrificial material was thermally decomposed to form nanosize voids within the films. The physical and electrical properties of the porous films were studied as a function of the reactivity of the sacrificial polymer with the glass, and the loading and molecular weight of the sacrificial polymer. Transmission electron microscopy was used to evaluate the porous microstructure. Cross-sectional images show pores of nearly spherical geometry with 5-20 nm diam. The dielectric constant and the index of refraction of the porous MSQ were lower after the decomposition of the sacrificial material. The dielectric constant decreased from 2.7 for a nonporous MSQ film to ϳ2.2 for a film with 30 wt % loading of the sacrificial polymer. In a similar way, the index of refraction was reduced from 1.42 to 1.29 for the porous MSQ film. The mechanical properties were evaluated using nanoindentation techniques. This paper focuses on the significant improvements observed upon introduction of porosity to the films. The fracture toughness, or the resistance to crack propagation, increased dramatically with porosity, as compared with the nonporous MSQ films. As a result, thicker MSQ films can be fabricated without spontaneous cracking. The elastic modulus and the hardness of the porous films were measured and showed a reduction in both properties with increasing porosity in the film.

Mechanical properties of porous methyl silsesquioxane and nanoclustering silica films using atomic force microscope

“…The average Young's modulus and hardness for nonporous MSQ (k = 2.80) are reported as 4.41 and 0.28 GPa, respectively [28]. As expected, making the material porous reduces the modulus to 2.31 and 1.94 GPa for porosities p = 0.33 (k = 2.4) and p = 0.49 (k = 2.0), respectively.…”

New approach to nanocomposites of polyimides containing polyhedral oligomeric silsesquioxane for dielectric applications

“…Homogeneous and closed pores with size in the nanometer range are preferred from the point of view of preserving the electric and mechanical properties of the material. The introduction of air gaps into interconnect structures and nanopores into polymers to reduce their dielectric constants have become an attractive approach [2][3][4][5]. An alternative approach to the preparation of porous low-j polyimides (PIs) is through the creation of voids by thermal degradation of the poly(propylene oxide) block of a phase-separated polyimide-poly(propylene oxide) block copolymer [6,7].…”

A Century of Dielectric Science and Technology

“…Other material formulations intentionally incorporate porosity into the material during processing. 54,55 The porous regions have a dielectric constant of 1.0, thereby lowering the overall dielectric constant of the material. Of course, the quintessential low-k material is air; as a result, studies have been undertaken that generate or incorporate air gaps between metal layers in device structures.…”