Analysis of the substrate effects of strain-hardening thin films on silicon under nanoindentation |
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| Authors: | TH Wang TH Fang YC Lin |
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| Institution: | (1) Department of Engineering Science, National Cheng Kung University, Tainan, 701, Taiwan, R.O.C.;(2) Stress-Reliability Laboratory, Advanced Semiconductor Engineering Inc., Kaohsiung, 811, Taiwan, R.O.C.;(3) Institute of Mechanical & Electromechanical Engineering, National Formosa University, Yunlin, 632, Taiwan, R.O.C.;(4) Center for Micro/Nano Technology, National Cheng Kung University, Tainan, 701, Taiwan, R.O.C. |
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| Abstract: | Mechanical properties of thin films on substrates can be evaluated directly through nanoindentation. For a comprehensive study,
thin films should be characterized via Young’s modulus, yield stress and strain-hardening exponent at constant temperature.
In this paper, we evaluate these effects of thin films on silicon substrate through finite element analysis. Thin films, from
soft to hard relative to the silicon substrate, are investigated in three categories: soft films on hard substrates, soft
to hard films on no elastic mismatch substrates, and hard films on soft substrates. In addition to examining the load-displacement
curve, the normalized hardness versus normalized indentation depth is checked as well to characterize its substrate effect.
We found that the intrinsic film hardness can be acquired with indentation depths of less than 12% and 20% of their film thickness
for soft films on hard substrates and for soft to hard films on no elastic mismatch substrates, respectively. Nevertheless,
nanoindentation of hard films on soft substrates cannot determine the intrinsic film hardness due to the fact that a soft
substrate cannot support a hard film. By examining the von Mises stresses, we discovered a significant bending phenomenon
in the hard film on the soft substrate.
PACS 61.43.Bn; 62.20.-x; 68.03.Hj; 68.05.Cf; 68.08.De |
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