Abstract
Elastic modulus and residual stress in freestanding ultrathin films (<100 nm) are characterized using bilayer cantilevers. The cantilevers comprise a test film and a well-characterized reference material (SU-8). When released from the substrate, residual stresses in the bilayer cantilever cause it to deflect with measurable curvatures, allowing the determination of both stiffness and residual stress of the test film. The technique does not require sophisticated mechanical test equipment and serves as a useful metrology tool for characterizing coatings immediately after fabrication in a clean room assembly line. The measured biaxial modulus and residual strain of 75 nm copper films are 211 ± 19 GPa and (7.05 ± 0.22) × 10−3, respectively. Additional experiments on the freestanding structures yield a mean Young’s modulus of 115 GPa. These properties are in close agreement with those measured from additional residual stress–driven structures developed on the same coatings by the authors.
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E. Arzt: Size effects in materials due to microstructural and dimensional constraints: A comparative review. Acta Mater. 46, 5611–5626 (1998).
E.N. Hahn and M.A. Meyers: Grain-size dependent mechanical behavior of nanocrystalline metals. Mater. Sci. Eng., A 646, 101–134 (2015).
A.H. Chokshi, A. Rosen, J. Karch, and H. Gleiter: On the validity of the Hall–Petch relationship in nanocrystalline materials. Scr. Metall. 23, 1679–1683 (1989).
M.A. Haque and M.T.A. Saif: Mechanical behavior of 30–50 mn thick aluminum films under uniaxial tension. Scr. Mater. 47, 863–867 (2002).
B. Budiansky and R.J. O’Connell: Elastic-moduli of a cracked solid. Int. J. Solids Struct. 12, 81–97 (1976).
H.B. Huang: Mechanical properties of freestanding polycrystalline metallic thin films and multilayers. Ph.D. thesis, Harvard University, Cambridge, Massachusetts, 1998.
C.W. Nan, X.P. Li, K.F. Cai, and J.Z. Tong: Grain size-dependent elastic moduli of nanocrystals. J. Mater. Sci. Lett. 17, 1917–1919 (1998).
S.R. Phillpot, D. Wolf, and H. Gleiter: Molecular-dynamics study of the synthesis and characterization of a fully dense, 3-dimensional nanocrystalline material. J. Appl. Phys. 78, 847–861 (1995).
K. Zhou: Effects of grain size and shape on mechanical properties of nanocrystalline copper investigated by molecular dynamics. Mater. Sci. Eng., A 615, 92–97 (2014).
B.C. Okolo: Stress and microstructure of sputter deposited thin copper and niobium films. Ph.D. thesis, Universitätsbibliothek der Universität Stuttgart, Stuttgart, 2003.
X.X. Li: Ultrathin single-crystalline-silicon cantilever resonators: Fabrication technology and significant specimen size effect on Young’s modulus. Appl. Phys. Lett. 83, 3081–3308 (2003).
S. Suresh, T.G. Nieh, and B.W. Choi: Nano-indentation of copper thin films on silicon substrates. Scr. Mater. 41, 951–957 (1999).
J.J. Vlassak and W.D. Nix: A new bulge test technique for the determination of Young modulus and Poisson’s ratio of thin-films. J. Mater. Res. 7, 3242–3249 (1992).
G.D. Sim, J.H. Park, M.D. Uchic, P.A. Shade, S.B. Lee, and J.J. Vlassak: An apparatus for performing microtensile tests at elevated temperatures inside a scanning electron microscope. Acta Mater. 61, 7500–7510 (2013).
J.Y. Chang, G.P. Yu, and J.H. Huang: Determination of Young’s modulus and Poisson’s ratio of thin films by combining sin2ψ X-ray diffraction and laser curvature methods. Thin Solid Films 517, 6759–6766 (2009).
M. Coulombier, G. Guisbiers, M.S. Colla, R. Vayrette, J.P. Raskin, and T. Pardoen: On-chip stress relaxation testing method for freestanding thin film materials. Rev. Sci. Instrum. 83, 9 (2012).
A. Favache: A generic “micro-stoney” method for the measurement of internal stress and elastic modulus of ultrathin films. Rev. Sci. Instrum. 87, 9 (2016).
T.P. Weihs, S. Hong, J.C. Bravman, and W.D. Nix: Mechanical deflection of cantilever microbeams—A new technique for testing the mechanical-properties of thin-films. J. Mater. Res. 3, 931–942 (1988).
G.K. Cuddalorepatta, H. Li, D. Pantuso, and J.J. Vlassak: Stress–strain behavior of freestanding ultra thin films (2019). Manuscript in preparation.
G.K. Cuddalorepatta, W.M. van Rees, H. Li, D. Pantuso, L.N. Mahadevan, and J.J. Vlassak: Poisson’s ratio and residual strain of freestanding ultra thin films. J. Mech. Phys. Solids (2019). Manuscript in preparation.
H. Lorenz, M. Despont, N. Fahrni, N. LaBianca, P. Renaud, and P. Vettiger: SU-8: A low-cost negative resist for MEMS. J. Micromech. Microeng. 7, 121–124 (1997).
M. Hopcroft, T. Kramer, G. Kim, K. Takashima, Y. Higo, D. Moore, and J. Brugger: Micromechanical testing of SU-8 cantilevers. Fatigue Fract. Eng. Mater. Struct. 28, 735–742 (2005).
H. Landolt and R. Börnstein: Single Crystal Elastic Constants and Calculated Aggregate Properties: A Handbook (Springer-Verlag, Berlin, 1979).
J. Schiotz, F.D. Di Tolla, and K.W. Jacobsen: Softening of nanocrystalline metals at very small grain sizes. Nature 391, 561–563 (1998).
D. Prokoshkina and V.A. Esin: Grain boundary width, energy and self-diffusion in nickel: Effect of material purity. Acta Mater. 61, 5188 (2013).
G.D. Sim, Y.S. Choi, D. Lee, K.H. Oh, and J.J. Vlassak: High tensile strength of sputter-deposited ZrB2 ceramic thin films measured up to 1016 K. Acta Mater. 113, 32–40 (2016).
J.D. Eshelby: The determination of the elastic field of an ellipsoidal inclusion and related problems. Proc. R. Soc. London, Ser. A 241, 376–396 (1957).
H.B. Huang and F. Spaepen: Tensile testing of free-standing cu, ag and al thin films and Ag/Cu multilayers. Acta Mater. 48, 3261–3269 (2000).
H.M. Ledbetter and E.R. Naimon: Elastic properties of metals and alloys. II. Copper. J. Phys. Chem. Ref. Data 3, 897 (1974).
S.S. Keller, G. Blagoi, M. Lillemose, D. Haefliger, and A. Boisen: Processing of thin SU-8 films. J. Micromech. Microeng. 18, 10 (2008).
M. Nordstrom, S. Keller, and M. Lillemose: SU-8 cantilevers for bio/chemical sensing; fabrication, characterization and development of novel read-out methods. Sensors 8, 1595–1612 (2008).
S.J. Lee, W. Shi, P. Maciel, and S.W. Cha: Top-edge profile control for SU-8 structural photoresist. In Proceedings of the 15th Biennial University/Government/Industry Microelectronics Symposium (Cat. No. 03CH37488) (IEEE, Boise, Idaho, 2003); pp. 389–390.
C.V. Thompson: Structure evolution during processing of polycrystalline films. Annu. Rev. Mater. Sci. 30, 159–190 (2000).
L.B. Freund, J.A. Floro, and E. Chason: Extensions of the stoney formula for substrate curvature to configurations with thin substrates or large deformations. Appl. Phys. Lett. 74, 1987 (1999).
R.W. Schafer: What is a Savitzky–Golay filter? [lecture notes]. IEEE Signal Process. Mag. 28, 111–117 (2011).
Acknowledgments
The work presented in this paper was supported by Intel Corporation. The test structures were fabricated at the Integrated Sciences Cleanroom and Nanofabrication Facility at Boston College, the Harvard University Center for Nanoscale Systems (CNS), which is supported by the National Science Foundation under NSF ECCS award No. 1541959, and Materials Research Science and Engineering Center at Harvard University, which is supported by the National Science Foundation under Award No. DMR-14-20570.
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Cuddalorepatta, G.K., Sim, GD., Li, H. et al. Residual stress–driven test technique for freestanding ultrathin films: Elastic behavior and residual strain. Journal of Materials Research 34, 3474–3482 (2019). https://doi.org/10.1557/jmr.2019.278
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DOI: https://doi.org/10.1557/jmr.2019.278