Journal of Materials Research

Articles

The effect of porogen loading on the stiffness and fracture energy of brittle organosilicates

Han Lia1, Youbo Lina1, Ting Y. Tsuia2 and Joost J. Vlassaka3 c1

a1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138

a2 Chemical Engineering Department, University of Waterloo, Nanotechnology Institute, Waterloo, Ontario N2L 3G1, Canada

a3 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138

Abstract

Integrating porous low-permittivity dielectrics into Cu metallization is one of the strategies to reduce power consumption, signal propagation delays, and crosstalk between interconnects for the next generation of integrated circuits. The porosity and pore structure of these low-k dielectric materials, however, also affect other important material properties in addition to the dielectric constant. In this paper, we investigate the impact of porogen loading on the stiffness and cohesive fracture energy of a series of porous organosilicate glass (OSG) thin films using nanoindentation and the double-cantilever beam (DCB) technique. The OSG films were deposited by plasma-enhanced chemical vapor deposition (PECVD) and had a porosity in the range of 7−45%. We show that the degree of porogen loading during the deposition process changes both the network structure and the porosity of the dielectric, and we resolve the contributions of both effects to the stiffness and fracture energy of the films. The experimental results for stiffness are compared with micromechanical models and finite element calculations. It is demonstrated that the stiffness of the OSG films depends sensitively on their porosity and that considerable improvements in stiffness may be obtained through further optimization of the pore microstructure. The cohesive fracture energy of the films decreases linearly with increasing porosity, consistent with a simple planar through-pore fracture mechanism.

(Received April 4 2008)

(Accepted September 16 2008)

Key Words:

  • Elastic properties;
  • Fracture;
  • Porosity

Correspondence:

c1 Address all correspondence to this author. e-mail: vlassak@esag.deas.harvard.edu

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