Quantifying improvements in adhesion of platinum films on brittle substrates
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N.R. Moody Sandia National Laboratories, Livermore, California 94550-0969
D.F. Bahr School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington 99164-2920 (Received 17 November 2003; accepted 22 March 2004)
This study used nanoindentation coupled with stressed overlayers to evaluate the effect of titanium interlayers on the interfacial fracture energy of platinum films on SiO2 substrates. Interfacial fracture energy was calculated three ways: from platinum buckles that formed spontaneously upon deposition of the film, from buckles that formed upon deposition of a stressed tungsten overlayer, and from blisters triggered by indentation of a platinum film with a tungsten stressed overlayer. The calculated values for the interfacial fracture energy of the Pt-SiO2 interface were 0.2 and 0.5 J/m2 for indentation blisters and spontaneous buckles, respectively. The effect of a titanium interlayer on adhesion was examined using a tungsten stressed overlayer coupled with nanoindentation. The addition of a titanium layer improved the adhesion of the platinum film on SiO2 from 0.2 to 1.0 J/m2. I. INTRODUCTION
The adhesion of thin films is an important property for performance and reliability of many thin film microelectronic devices. Failure of these devices can occur if the thin films delaminate from one another. To ensure that the device will not fail, it is important to know the amount of energy it takes for the films to delaminate, or the interfacial fracture energy [⌫(⌿)]. This value, also called the practical work of adhesion, takes into account the thermodynamic work of adhesion between the materials at the interface and the energy dissipated by the film and substrate.1 The energy dissipated includes inelastic contributions from ligament bridging, plasticity at the interfacial crack tip and friction between the tip and film.2 The practical work of adhesion can be determined qualitatively or quantitatively depending on the test method.3 Different methods to calculate the adhesion energy, or interfacial fracture energy, have been developed. Some methods use a microprobe to scratch4–7 or indent8–12 the surface. Scratch testing continuously measures the force and displacement of the microprobe, generally a diamond tip, to generate an interfacial crack and spalling. Nanoindentation can be used to either induce spontaneous buckling of the film or to create indentation blisters, depending on the residual stress of the film. Four-point DOI: 10.1557/JMR.2004.0232 1818
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 6, Jun 2004 Downloaded: 08 Apr 2015
bend and sandwich specimens test a macroscopic sample that incorporates a thin film into its structure.13 The thin film is usually incorporated using diffusion bonding which can alter the film’s microstructure and interface properties, and as a result do not test the as-deposited state of films. Another adhesion test method is the stressed overlayer, or superlayer, method.14–15 The stressed overlayer method uses a highly compress
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