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Indentation Fracture and How to Apply to Thin Films. Huai Huang. Outline. Indentation test Indentation fracture mechanics Stress field and Crack system Fracture Mechanics Analysis Fracture toughness measurement on thin film. What is Indentation test. Easy and cheap to perform:

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Presentation Transcript
outline
Outline
  • Indentation test
  • Indentation fracture mechanics
    • Stress field and Crack system
    • Fracture Mechanics Analysis
  • Fracture toughness measurement on thin film
what is indentation test
What is Indentation test
  • Easy and cheap to perform:
  • Properties:
    • Elastic properties : Modulus
    • Plastic properties: Hardness
    • Time dependent properties: Creep
    • Fracture properties
hertzian stress field
Hertzian Stress field
  • For smooth sperical indenter
hertzian cone crack
Hertzian cone crack

However X can’t be exactly calculated

indentation stress field
Indentation Stress field

For a normal point load P the stress field can be given by Boussinesq field:

radial median crack
Radial-median crack
  • Under a point load
fracture mechanics analysis
Fracture Mechanics Analysis

System behave like a center-loaded, half-penny crack, for which the stress intensity factor is given by:

The stress field can be expressed (by Hill’s expending cavity solution) as:

Combining the above two equations and assuming the crack arrests when it grows to a length at which the stress intensity factor is just equal the fracture toughness

Experiment within 40% accuracy

other fracture property
Other Fracture property
  • Inert Strength
  • R-curves
  • Crack-velocity exponent
  • Crack initiation
  • Crack propagation
hard film on a soft substrate
Hard film on a soft substrate
  • Load vs displacement can be simulated as
indentation fracture for thin film
Indentation fracture for thin film
  • Mechanical properties were extracted from displacement profile minima
  • Typical loads 1000gram and crack length 100um: Small crack threshold need.
  • Solution: Change of indenter geometry

sharper indenter needed to reduce critical load

    • Vickers indenter: threshold 25 grams
    • Cube corner indenter: 0.5 grams
    • (Same theory can be apply to different indenters)
indentation on low k
Equation should not be directly applied, Since the crack shape is not half-penny shape.

As a first order approximation, Equation can be used to estimate the low-K films fracture toughness. Low-K dielectric films fracture toughness was estimated to range from 0.01 to 0.05 MPa·m1/2

Indentation on Low K
summary
Summary
  • Indentation test can provide fracture property such as fracture toughness. Indentation Fracture mechanics is discussed.
  • Reduced crack threshold load can apply indentation test to very thin film.
  • Theoretical explanations (include analytical or FEM simulation solution) of thin film indentation fracture are needed.
references
References
  • 1, M. F. Doerner and W. D. Nix, A Method for Interpreting the Data form Depth-Sensing Indentation Instruments, J. Mater. Res. 1, 601-609 (1986)
  • 2. B. Lawn, R. Wilshaw, Indentation fracture: principles and applications, J. Mater. Sci. 10 (1975)
  • 3. B. lawn, Fracture of Brittle Solids (second edition), Cambridge University Press, pp.249-306, (1993)
  • 4. G.M. Pharr, D.S. Harding, W.C. Oliver, Mechanical Properties and Deformation Behavior of Materials Having Ultra-Fine Microstructures, M. Nastasi et al. (eds.), Kluwer Academic Press, pp. 449-461, (1993)
  • 5. I. S. Adhihetty, J. B. Vella, Alex A. Volinsky, el., Mechanical Properties, adhesion, and fracture toughness of low-k dielectric thin films for microelectronic applicatons, Mechanics and Materials Summer Conference, San Diego, June, 2001
  • 6. J. B. Vella, I. S. Adhihetty, K Junker, A. A. Volinsky, Mechanical properties and fracture toughness of organo-silicate glass (OSG) low-k dielectric thin films for microelectronic applications, International Journal of Fracture, 119/120, pp.487–499, (2003)
  • 7. A. A. Volinskya , W. W. Gerberichb, Nanoindentaion techniques for assessing mechanical reliability at the nanoscale, Microelectronic Engineering 69 (2003) 519–527
  • 8. J. B. Vella, A. A. Volinsky I.S. Adhihetty1,el.,Nanoindentation of Silicate Low-K Dielectric Thin Films, Mat. Res. Soc. Symp. Proc. Vol. 716 (2002)
  • 9. A.A.Volinsky, J.B.Vella, and W.W. Gerberich, Fracture toughness, adhesion and mechnical properties of low-K dielectric thin films measured by nanoindentation, Thin Solid Films 429(1-2), 201–210, (2003)