Perfect Conformal Deposition of Electroless Cu for High Aspect Ratio Through-Si Vias

Abstract

In three-dimensional integration technology, through-silicon vias ͑TSVs͒ with a high aspect ratio in excess of 10 are required, due to a strong demand for a higher packing density. We achieved perfect conformal electroless plating of Cu by the addition of Cl − and bis͑3-sulfopropyl͒ disulfide to a standard plating bath. With this technology, the Cu thickness of the TSV sidewalls remained constant with depth, even for the TSV with an aspect ratio of 20. Perfect conformal plating is a promising technology that could lower the resistance of high aspect ratio TSVs.The formation of through-silicon vias ͑TSVs͒ to enable the stacking of multiple layers of thin Si substrates is a key technology for three-dimensional integration. It is expected that the minimum pitch of TSVs is smaller than 10 m, which will require the diameter of the TSVs to decrease below a few micrometers in the near future. 1,2 In such a structure, the TSV will take the place of a largescale integration circuit global interconnection. Cu filling of the TSV is an important technology because it enables a lower resistance TSV than chemical vapor deposition of tungsten ͑CVD-W͒ filling by an order of magnitude; however, there have been many technical problems in Cu filling of a high aspect ratio TSV. Cu electroplating technology has been studied extensively, 3 and a socalled superconformal deposition that enables a bottom-up fill of submicrometer vias has been proposed. [4][5][6][7][8][9][10][11][12][13] In Cu electroplating, the formation of a sputtered Cu seed layer is very difficult for a high aspect ratio via because the film thickness at the sidewall is much lower than on the flat surface. Therefore, conformal deposition using chemical vapor deposition of titanium nitride ͑CVD-TiN͒ or CVD-W was studied before Cu electroplating. 14-16 However, it is not easy to fill a high aspect ratio via by superconformal Cu electroplating.Cu electroless plating can result in good conformal deposition and is rather insensitive to the electrical conductivity of the seed layer. We found that a bottom-up fill was possible for a submicrometer ultra-large scale integration via using Cu electroless plating with the addition of a sulfuric organic compound with polyethylene glycol ͑PEG͒. We found that a sulfuric organic compound such as bis͑3-sulfopropyl͒ disulfide ͑SPS͒ acted as a strong inhibitor. 17,18 The diffusion of inhibitor molecules into the bottom of fine holes is limited, resulting in faster growth of Cu within the via. Furthermore, Cu can be deposited on TaN, WN, and W barrier layers without a Pd catalyst through displacement plating mechanisms. 19,20 In the preliminary stages of this study, we attempted to use an SPS-contained plating bath to fill TSVs. However, these additives were unable to achieve a bottom-up fill of high aspect ratio TSVs with diameters of a few micrometers. In this study, we investigated Cu-filling characteristics when adding Cl − as a third additive to a PEG and a sulfuric organic compound plating bath. ExperimentalWe prepared the TSV sam...

Conformal Electroless Deposition of Barrier and Cu Seed Layers for Realizing All-Wet TSV Filling Process

“…The addition of SPS and chloride ions inhibits electroless Cu plating [6]. In addition, the diffusion flux of inhibitors, Cu-EDTA complex and reducing agent were in balance throughout the TSV.…”

“…After formation of the electroless barrier layer, Cu was deposited directly on the barrier layer by electroless displacement plating at 70 °C with a glyoxylic acid bath. In addition, SPS and chloride ions were added as inhibitors [6]. Finally, the TSV was filled with electroplated Cu using Cu sulfate and a sulfuric acid bath.…”

Physicochemical effects of seed structure and composition on optimized TSV fill performance

“…Electroless TSV filling has been an area of active research for many years [8], with good results for bottom-up filling [9] and barrier deposition [10] reported. Figure 1(b) shows the steps of the Electroless TSV filling process.…”

Stability Evaluation of Non-Agglomerated Pd Nanoparticle Catalyst Dispersion for Electroless Deposition

“…However, these methods require high processing temperatures. Electroless plating (ELP) is an alternative candidate for TSV metallization because of its uniform conformal deposition, low cost, and low temperature [5][6][7].…”