Metallization of micro through silicon via (TSV) is vital in 3-dimensional integration of chips and high-density printed circuit boards. As the diameter decreases and aspect ratio increases, realizing a uniform copper seed layer inside TSV becomes increasingly challenging by using traditional techniques of high-cost physical vapor deposition (PVD) and chemical vapor deposition (CVD). Cu electroless deposition (Cu-ELD) is a promising technique for growing a conductive seed layer on the wall of TSV, and promotes the completion of metallization of micro TSV following by Cu electroplating. In the current study, an advanced method is developed to form Cu seed layer on micro TSV by Cu-ELD catalyzed through Ag nanoparticles. The Ag nanoparticles are synthesized using gallic acid as the reducing agent (denoted as GA-Ag NPs). Ultraviolet–visible absorption spectroscopy and transmission electron microscopy are applied to study the mechanism of conformal Cu-ELD catalyzed by GA-Ag NPs, and results demonstrate that all Ag ions are reduced to spherical Ag NPs of 9.7 nm in average size. Electrochemical tests and finite element simulation illustrate that the high catalytic activity of GA-Ag NPs facilitates Cu-ELD to achieve an effective conformal deposition in TSV. The obtained continuous and uniform Cu seed layer enables the void-free filling of TSV ultimately by Cu electroplating. An in situ XRD device is designed and built up for investigation of Cu-ELD process, which reveals that the Cu layer catalyzed by GA-Ag NPs during growth is stable and exhibits a mixed crystalline structure with texture coefficient ( TC ) values of Cu (220) and Cu (311) close to and higher than 25 %.
In this work, we combined the computational simulation and experiments to explore the convection on filling characteristics of the micro through-holes (THs) with multiple aspect ratio (ARs). The micro THs with ARs 6.25:1∼1.67:1 (thickness 500 μm) were chosen as research targets. The computational model was established based on the actual state of Haring-Cell, and attention was fixed on the convection distribution in the micro THs. The interaction mechanism of additives with the changing ARs systematically explored by electrochemical measurements. The simulation results show that the convection in the micro THs center declines with the increasing AR. The convection-dependent additives formed diverse adsorption states around the micro THs with different ARs, providing two kinds of Cu filling processes, including defect-free filling and insufficient filling. The weak convection is conducive to the adsorption of the accelerator and detrimental to the adsorption of the suppressor, which accelerates the Cu electrodeposition and elevates the throwing power (TP) value to over 100% to form the defect-free filling. Strong convection is instrumental in the adsorption of the leveler so that a uniform Cu film thickness can be obtained but to create the insufficient filling. Simulation and electroplating experiments show that the AR of 3.33:1 is the cut-off point of the flow field distribution and the electroplating processes. The micro THs with AR higher than 3.33:1 can be fully filled with a uniform bright Cu surface.
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