Study on the effects of pressure and material characterization in thin film and TSV fabricated by supercritical carbon dioxide electrolyte

Supercritical CO2 (sc-CO2), post sc-CO2 and traditional electroplating are used to fabricate Cu metal thin films. The effects of adjusting electroplating pressure over grain size, preferred grain orientation, mechanical properties and sheet resistance are discussed in this work. Additionally, through silicon vias (TSV) with an aspect ratio of 1:4 were fabricated by the three methods presented, and their influence over electrical resistance of the Cu pillar was observed. From the results it was clear that sc-CO2 process provides the fastest micro-hole filling at 4 h, followed by post sc-CO2 process at 5 h and lastly, traditional process at 36 h. Moreover, grain size produced by the sc-CO2 process was smallest, calculated at 20 nm; second smallest was by post sc-CO2 process at around 27 nm, and the largest was traditional process at around 38 nm. Fabrication process had an evident effect over grain size, hence affecting the mechanical and electrical properties of the structures. It is revealed that thin films produced by sc-CO2 process have highest hardness, highest internal stresses and lowest roughness at 64-67 Hv, 45-54 MPa, and 0.68-0.85 mu m, respectively; traditional process had the lowest values at 57 Hv, 30 MPa and 1.15 mu m respectively; and post sc-CO2 process was intermediate at 58-62 Hv, 33-41 MPa and 0.95-1.10 mu m, respectively. In sheet resistance measurements, the trend persists and the highest values were displayed by the sc-CO2 process at 1.3-1.5 mu Omega-cm, the lowest by traditional process at 1.1 mu Omega-cm, and post sc-CO2 process was intermediate at 1.2-1.3 mu Omega-cm. For TSV Cu pillars, the sc-CO2 process displayed the highest electrical resistance at 5 m Omega, second largest was post sc-CO2 process at 1.5 m Omega and the smallest was traditional process at 1.1 m Omega. Sc-CO2 electroplating described in this work was performed without any additives, and still produced a high degree of grain refinement and excellent filling capabilities. (C) 2016 Elsevier Ltd. All rights reserved.