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RESEARCH PAPERS

# Viscoelastic Characterization of Low-Dielectric Constant SiLK Films Using Nanoindentation in Combination With Finite Element Modeling

[+] Author and Article Information
J. M. den Toonder

Philips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlandsjaap.den.toonder@philips.com Philips Centre for Industrial Technology, P.O. Box 218, 5600 MD Eindhoven, The Netherlandsjaap.den.toonder@philips.com Philips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlandsjaap.den.toonder@philips.com Philips Centre for Industrial Technology, P.O. Box 218, 5600 MD Eindhoven, The Netherlandsjaap.den.toonder@philips.com

Y. Ramone, A. R. van Dijken, J. G. Beijer

Philips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands Philips Centre for Industrial Technology, P.O. Box 218, 5600 MD Eindhoven, The Netherlands Philips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands Philips Centre for Industrial Technology, P.O. Box 218, 5600 MD Eindhoven, The Netherlands

G. Q. Zhang

Philips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlandsg.q.zhang@philips.com Philips Centre for Industrial Technology, P.O. Box 218, 5600 MD Eindhoven, The Netherlandsg.q.zhang@philips.com Philips Research Laboratories, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlandsg.q.zhang@philips.com Philips Centre for Industrial Technology, P.O. Box 218, 5600 MD Eindhoven, The Netherlandsg.q.zhang@philips.com

J. Electron. Packag 127(3), 276-285 (Aug 12, 2004) (10 pages) doi:10.1115/1.1938990 History: Received June 21, 2004; Revised August 12, 2004

## Abstract

SiLK is a polymer material developed for use as a thin-film dielectric in the interconnect structure of high-density integrated circuits. Among others, its thermomechanical properties play a dominant role for the integrity and reliability of the interconnect during processing, testing, and use. Being a polymer, SiLK may show viscoelastic (time-dependent) behavior. In this paper, we use nanoindentation techniques in combination with analytical and finite element modeling (FEM) to determine the viscoelastic properties of a thin SiLK film on a silicon substrate. Indentation-creep experiments show that this SiLK film indeed responds in a viscoelastic way. This may be caused by the non fully cross-linked test samples prepared using nonstandard processing. Using the FEM simulation, we find that the behavior of this thin SiLK film can be described with a linear viscoelastic model up to the characteristic stress and strain levels of approximately $200MPa$ and 3%, respectively. For higher stress and strain levels, the response becomes nonlinear. The results are validated with independent indentation load-unload measurements.

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## References

SiLK is a trademark of the DOW Chemical Company.

## Figures

Figure 1

The principle of indentation (top); a typical indentation load-displacement curve (bottom)

Figure 2

SEM of the spherical indenter tip (top); tip calibration curve (bottom)—hc denotes the contact depth, i.e., the depth over which the sphere makes contact with the material

Figure 3

The full finite element mesh (top); magnification of the contact region (bottom)

Figure 4

Figure 5

Typical experimental indentation-creep curves with creep load 1mN (top), and 20mN (bottom)

Figure 6

Elongational relaxation modulus found from a theoretical analysis of the creep measurements

Figure 7

Simulated load-unload curves for varying Young’s modulus of the SiLK layer, elastic computation

Figure 8

Elongational creep modulus found from the quasi-elastic numerical analysis of the creep curves

Figure 9

Simulated and measured indentation-creep curves for the 1mN creep load. In the simulations, a linear viscoelastic model was used for SiLK, in which the parameters were adjusted to obtain good agreement with the measurements (see Table 2)

Figure 10

Simulated and measured indentation-creep curves. In the simulations, a linear viscoelastic model was used for SiLK with parameters, as in Table 2

Figure 11

Measured and predicted load-unload curves. In the simulated predictions, a linear viscoelastic model was used for SiLK with parameters, as in Table 2

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