Defforge et al. Nanoscale Research Letters 2012, 7:375 http://www.nanoscalereslett.com/content/7/1/375 Page 6 of 7 Figure 6 Filling quality of the macropores with copper. SEM polished, sliced views of copper-filled macropores comparing the filling quality of macropores with copper. (a) Using a non-accurate electrolytic solution (JGB concentration equal to 5 ppm) leads to void formation during the copper growth. (b) Using an adapted electrolyte (JGB concentration was increased to 10 ppm) leads to the formation of void-free copper deposition. apposed on the copper-filled macropores and connected each other, thanks to the remaining backside nucleation layer (Figure 8). Voltamperometric scans were per- formed on a range of 0 to 100 mA to determine the re- sistance of the TSV. This resistance was found equal to 0.98 mΩ/32 via. After calculation, the resistance per via was found around 32 mΩ. The resistivity of the copper into the pores is approximately 1.78 μΩ cm; this value is 1.06 times higher than the theoretical copper resistivity (ρ(Cu th.) = 1.67 μΩ cm) [27]. This measurement was per- formed several times to ensure a stable average resist- ance value. These results are better than those obtained in the literature for DRIE TSV [28]. The high copper conductivity into the pores may be explained by the slower deposition kinetic that limits void formation. Conclusion After the determination of the different strategies to fab- ricate local TSV from macropore arrays, the selective opening of almost through-silicon macropores was chosen. Using a simple photolithography step, this tech- nique enabled the local formation of highly conductive TSV. Macropores of 15-μm pitch and 12-μm wide were, thus, etched into a HF-based solution and then select- ively filled with copper by a potentiostatic deposition technique during 6 h. During the deposition step, the electrolyte composition must be optimized to ensure void-free copper growth. Then, for the first time, the via resistivity was measured in a low-cost, full electrochem- ical (etching and filling) TSV fabrication process. The Figure 7 Local formation of copper micropillar array. SEM view of copper micropillar array formation after local copper growth into through-silicon macropore array followed by complete silicon removal by alkaline etching (KOH at high temperature). Figure 8 Schematic representation of through-silicon macropore electrical characterization. The four probes were apposed on the via and connected each other with the backside nucleation layer.