Indentation Fracture and How to Apply to Thin Films

1. Indentation Fracture and How to Apply to Thin Films Huai Huang

2. Outline • Indentation test • Indentation fracture mechanics • Stress field and Crack system • Fracture Mechanics Analysis • Fracture toughness measurement on thin film

3. What is Indentation test • Easy and cheap to perform: • Properties: • Elastic properties : Modulus • Plastic properties: Hardness • Time dependent properties: Creep • Fracture properties

4. Hertzian Stress field • For smooth sperical indenter

5. Hertzian cone crack However X can’t be exactly calculated

6. Indentation Stress field For a normal point load P the stress field can be given by Boussinesq field:

7. Radial-median crack • Under a point load

8. 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

9. Other Fracture property • Inert Strength • R-curves • Crack-velocity exponent • Crack initiation • Crack propagation

10. Hard film on a soft substrate • Load vs displacement can be simulated as

11. 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)

12. 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

13. 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.

14. 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)