Preferential grain orientation of copper (Cu) vias is speculated to result in a decrease in stresses in elastically anisotropic Cu.  On the other hand, highly twinned Cu microstructures are known to increase their electromigration resistance and mechanical properties, without significantly degrading electrical performance [1,2].  Therefore, the optimal manipulation of Cu via microstructure could enable the improvement of the reliability of microelectronic devices.  In this study, the “tuning” of the microstructure of Cu trenches were achieved by varying the bath’s chemical composition in different trench aspect ratios.  The organic additive system comprising of polyethylene glycol (PEG), bis-(sodium sulfopropyl)-disulfide (SPS), and janus green b (JGB) is commonly used in the electroplating of Cu into trenches and higher aspect ratio through-silicon vias (TSV) for microelectronics [3,4].  In this study, copper was pulse-electrochemically deposited (PED) into 500 nm deep trenches of various widths to evaluate the impact of aspect ratio on the evolution of copper microstructure.  Trench aspect ratios of 0.25, 1, 2, and 2.78 were investigated.  The organic additive concentrations in the PED bath were also adjusted to examine their influence on the Cu microstructure.  By metallurgical sample preparation and the focused ion beam (FIB) technique, the sample cross-sections of the Cu filled trenches were revealed for microstructural analysis using electron backscattering diffraction (EBSD).  From the EBSD data, the grain orientation and twin boundary distribution of the deposited Cu microstructure were analyzed.   

References:

1. L. Lu, X. Chen, X. Huang and K. Lu, Science, 323, 5914 (2009).

2. D. Xu, V. Sriram, V. Ozolins, J. Yang, K. N. Tu, G. R. Stafford, C. Beauchamp, I. Zienert, H. Geisler, P. Hofmann and E. Zschech, Microelectronic Engineering, 85, 10 (2008).

3. K. Kondo, T. Matsumoto and K. Watanabe, Journal of The Electrochemical Society, 151, 4 (2004).

4. M. Jung, Y. Song, T. Yim and J. Lee, Electronic Components and Technology Conference (ECTC), 2011 IEEE 61st, (2011).