Electroless deposition of Cu seed layer catalyzed by Ag nanoparticles for micro through silicon via metallization

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 %.