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U4.3.1

Nanoindentation and tensile behavior of copper films D. Read1 , R. Geiss1 , J. Ramsey2 , T. Scherban3,†, G. Xu3 , J. Blaine3 , B. Miner3 , and R.D. Emery4 1

National Institute of Standards and Technology, Boulder, CO 80305 Reed College, Portland, OR 97202 3 Logic Technology Development Quality & Reliability, Intel Corp., Hillsboro, OR 97124 4 Components Research, Intel Corp., Chandler, AZ 85226 2

†

Corresponding author: 503.613.1716, [email protected]

ABSTRACT The mechanical properties of ~ 10 µm thick electroplated copper films were investigated by both nanoindentation of supported films and microtensile testing of free-standing films. By utilizing both techniques to examine the same films, the results could be directly compared to one another. Nanoindentation yield strength was found to be 5 – 15 % lower than in the microtensile case. Differences were attributed to grain size differences and, for annealed films, the presence of internal stresses in supported films only. Data from both techniques generally followed the Hall-Petch trend. INTRODUCTION Two of the most common experimental techniques used in the study of the mechanical behavior of thin films are nanoindentation, used to study films on substrates [1], and uniaxial tensile testing, often used to examine free-standing films [2]. Nano indentation is a relatively simple test to perform; however, a detrimental aspect is that it imposes complex, non- uniform deformations to the specimen, making interpretation of the experimental results difficult. Tensile testing, on the other hand, applies a generally uniform and simple deformation. A further advantage is that preexisting residual stresses are removed prior to testing. The traditional drawback to this method is that it has been hard to perform, because of difficulties associated with specimen fabrication and handling. Therefore, it would be useful to develop a rigorous relationship between these two tests. Unfortunately, little work has been done to directly compare measurements from both techniques [3,4]. One relatively simple analytical expression relating the yield strength (here called Ny for nanoindentation yield strength) and the maximum indentation load, P, has been developed previously [1] and is commonly used

Ny =

3P 2πc 2

(1)

where c is the radius of the plastic zone around an indentation location. Ny has been referred to as the “yield strength” of the material being studied, but it is unclear exactly what stress this would correspond to in a uniaxial tensile test. Further, (1) does not consider the effects of internal stresses and strain hardening. The objective of the present study was to use both nanoindentation and tensile testing to characterize the room temperature mechanical behavior of the same copper films, and to use these results to look for correlations between the two techniques.

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