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MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ELECTROPLATED Cu THIN FILMS A.A. Volinsky*, J. Vella*, I.S. Adhihetty*, V. Sarihan*, L. Mercado*, B.H. Yeung*, and W.W. Gerberich** * TM Motorola, Digital DNA Labs, Semiconductor Product Sector, AZ ** University of Minnesota, Dept. of Chem. Eng. and Materials Science, Minneapolis, MN. ABSTRACT Copper films of different thicknesses of 0.2, 0.5, 1 and 2 microns were electroplated on top of the adhesion-promoting barrier layers on single crystal silicon wafers. Controlled Cu grain growth was achieved by annealing films in vacuum. The Cu film microstructure was characterized using Atomic Force Microscopy and Focused Ion Beam Microscopy. Elastic modulus of 110 to 130 GPa and hardness of 1 to 1.6 GPa were measured using the continuous stiffness option (CSM) of the Nanoindenter XP. Thicker films appeared to be softer in terms of the lower modulus and hardness, exhibiting a classical Hall-Petch relationship between the yield stress and grain size. Lower elastic modulus of thicker films is due to the higher porosity and partially due to the surface roughness. Comparison between the mechanical properties of films on the substrates obtained by nanoindentation and tensile tests of the freestanding Cu films is made. INTRODUCTION With the rapid change of materials systems and decreased feature size, thin film microstructure and mechanical properties have become critical parameters for microelectronics reliability. Thorough reliability and compatibility tests are required to integrate new low-K dielectric materials and novel interconnects (Cu). For most reliability tests, knowledge of the thin film constitutive mechanical behavior is required. Mechanical properties of thin films often differ from those of the bulk materials. This can be partially explained by the nanocrystalline structure of thin films and the fact that these films are attached to a substrate. Due to typically high yield strengths thin films can support very high residual stresses. This residual stress can be relieved later during processing or in the actual device operation through either thin film plastic deformation or interfacial delamination. Thermal expansion coefficient and elastic modulus mismatch are typically the properties that cause these device failures. Both elastic and plastic properties are important for thin film characterization. Thin film mechanical properties can be measured by tensile testing of freestanding films [1] and by the microbeam cantilever deflection technique [2-4], but the easiest way is by means of nanoindentation, since no special sample preparation is required and tests can be performed quickly and inexpensively. Nanoindentation is similar to conventional hardness tests, but is performed on a much smaller scale using very sensitive load and displacement sensing equipment. The force required to press a sharp diamond indenter into tested material is recorded as a function of indentation depth. Since the depth resolution is on the order of nanometers, it is possible to indent even very th