Quantitative adhesion measures of multilayer films: Part I. Indentation mechanics
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Quantitative adhesion measures of multilayer films: Part I. Indentation mechanics Michael D. Kriese and William W. Gerberich Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455
Neville R. Moody Sandia National Laboratories, Livermore, California 94551 (Received 1 June 1998; accepted 29 March 1999)
The mechanics for calculating the quantitative driving force of indentation-induced delamination of thin-film multilayers is presented. The solution is based on the mechanics developed by Marshall and Evans [D.B. Marshall and A.G. Evans, J. Appl. Phys. 56, 2632 (1984).] and extended to the general case of a multilayer by use of standard bending and thin-plate analyses. Presented and discussed are the specific solutions for the bilayer case that show that in the limit of zero thickness of either layer, the solution converges to the single-layer case. In the range of finite thickness, the presence of the superlayer increases the driving force relative to that possible for the original film alone and can be optimized to the experimental situation by proper choice of thickness, elastic constants, and residual stress. The companion paper “Quantitative adhesion measures of multilayer films: Part II. Indentation of W/Cu, W/W, Cr/W” discusses experimental results with copper, tungsten, and chromium thin films.
I. INTRODUCTION
Interfacial adhesion to substrates is critical to the reliability of devices using thin films and coatings; this fact is reflected in the numerous number of tests that have been developed to measure adhesion. However, most of the commonly used techniques are semiquantitative,2 because although they are useful for quality control and comparative purposes, the critical values of these tests cannot be directly related to material mechanisms of adhesion.3,4 Thus, a number of researchers have used linear elastic fracture mechanics to develop test methods that are truly quantitative, allowing direct assessment of the critical energies of interfacial adhesion.5–9 Quantitative values can then be directly related to energy-dissipative mechanisms both at the interface and within nearinterface regions of the film and substrate. Many of these mechanisms have been identified and explored for many practical and ideal film-substrate systems, but most of the experimental methods have been developed for macroscopic sandwich structures.10–15 In these methods, a film is deposited onto two substrates and subsequently bonded together before adhesion assessment. The bonding process, typically diffusion bonding under applied pressure, most often leads to changes at the interface and in the microstructure of the film; thus, the bonding process plays a role in the nature and magnitude of the energy-dissipative mechanisms. J. Mater. Res., Vol. 14, No. 7, Jul 1999
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There are a lesser number of thin film adhesion assessment methods that measure the film in the asprocessed c
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