Mechanical characterization and modeling of low-dielectric-constant SiLK films using nano-indentation: time- and temperature-effects

Abstract

<p>SiLK [1] semiconductor dielectric is a polymeric material developed for use as a thin film dielectric in the interconnect structure of high density integrated circuits. Among others, its thermo-mechanical properties play a dominant role for the integrity and reliability of the interconnect, during processing, testing and use. Being a polymer, SiLK films may show viscoelastic (time-dependent) behavior. In this paper, we use nano-indentation experiments to determine the viscoelastic properties of a thin SiLK film on a silicon substrate as a function of temperature within the range 25-100°C. Also, the effect of the degree of curing of the films on the viscoelastic properties is studied. The experiments indeed show that the SiLK film responds in a viscoelastic way. The viscoelastic behavior can be described by a linear viscoelastic generalized Maxwell model with a power law relaxation spectrum. The effect of temperature can be modeled by an Arrhenius time-temperature superposition in the temperature range 25-100°C. Thus, we obtain a full description of the viscoelastic properties of the SiLK film that can be directly implemented in a (commercially available) Finite Element Modeling package like Marc or Ansys. Furthermore, the degree of curing of the SiLK film clearly affects the viscoelastic properties. Within the range of cure index from 0.65 to 0.98, a significant change in the relaxation modulus is observed.</p>