Quantitative adhesion measures of multilayer films: Part II. Indentation of W/Cu, W/W, Cr/W
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Quantitative adhesion measures of multilayer films: Part II. Indentation of W/Cu, W/W, Cr/W 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)
Sputtered copper and tungsten thin films both with and without tungsten and chromium superlayers were tested by using nanoindentation probing to initiate and drive delamination. The adhesion energies of the films were calculated from the induced delaminations using the analysis presented in “Quantitative adhesion measures of multilayer films: Part I. Indentation mechanics.” Copper films ranging in thickness from 150 to 1500 nm in the as-sputtered condition had measured adhesion energies ranging from 0.2 to 2 J/m2, commensurate with the thermodynamic work of adhesion. Tungsten films ranging in thickness from 500 to 1000 nm in the as-sputtered condition had measured adhesion energies ranging from 5 to 15 J/m2. The superlayer was shown to induce radial cracking when under residual tension, resulting in underestimation of the adhesion energy when the film was well adhered. Under conditions of weak adherence or residual compression, the superlayer provided an excellent means to induce a delamination and allowed an accurate and reasonably precise quantitative measure of thin film adhesion.
I. INTRODUCTION
A quantitative understanding of the adhesion of thin films is necessary to fully explore and understand the mechanisms and allow the fullest exploitation of thin films for many critical applications, particularly within the semiconductor microelectronics industry. “Quantitative adhesion measures of multilayer films: Part I. Indentation mechanics,” hereafter referred to as Part I, developed the mechanics for the calculation of the driving force for an indentation-induced delamination of a multilayer. The mechanics are based on an extension of the analysis given by Marshall and Evans,1 for which the strain energy release rate is a function of the residual, indentation, and buckling stresses and strains. Part I derived solutions for the equivalent multilayer counterparts of these stresses and strains as a function of the order, thickness, and elastic constants of the individual layers. It was assumed that the individual layer thicknesses and residual stresses, the delamination diameter, and the indentation volume are known experimental values. The multilayer solution allows measurement of the critical driving force associated with an experimental delamination of an as-processed multilayer. Moreover, the solution allows optimization of a superlayer deposited for the purpose of increasing the driving force for delamination J. Mater. Res., Vol. 14, No. 7, Jul 1999
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of the underlying film while retaining the experimental ease of the indentation method and the st
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