Takumi Yokoyama

Study of low resistance TSV using electroless plated copper and tungsten-alloy barrier

We studied a low temperature deposition of tungsten-alloy barrier and copper layers only by electroless plating, with an aim of realizing low resistance TSV with a high aspect ratio. We succeeded in successive deposition of W-Ni-P barrier layer and Cu on SiO2. Furthermore, we found that the addition of Cl ions to SPS- and PEG- plating bath significantly improved the conformal deposition property even for a few μm in diameter TSVs with the aspect ratio higher than 10.

Formation and Evaluation of Electroless-Plated Barrier Films for High-Aspect-Ratio Through-Si Vias

The formation of a diffusion barrier layer in a through-Si via (TSV) has been studied with a combination of nanoparticle catalyst and electroless plating (ELP). We used Au-nanoparticles (Au-NPs) or Pd-nanoparticles (Pd-NPs) as catalysts for ELP of Ni- and Co-alloy barrier layers. We studied deposition of Ni–B and Co–B films in high-aspect-ratio (AR) TSV. Then, we succeeded in controlling the deposition profile of Ni–B in a high-AR TSV by the addition of bis(3-sulfopropyl)-disulfide (SPS). SPS turned out to be an inhibitor of electroless plating of Ni–B. On the other hand, the Co–B film was deposited conformally without additive. The electrical resistivity of Cu after annealing Cu/barrier stacked structure suggests that Co–B has better thermal stability than Ni–B.

Formation of electroless barrier for all-wet process of TSV in 3D-LSI technology and evaluation of its adhesion property

The fabrication of thin barrier metal layer in a high aspect ratio TSV using electroless plating with Pd nanoparticles (NPs) as a catalyst was investigated. We succeeded in the formation of thin continuous electroless barrier metal layer for a high aspect ratio TSV with addition of adequate amount of additives. Adhesion strength of Co-W-B barrier metal increased with decreasing film thickness. The adhesion strength of barrier film increased with annealing at 200 °C, and it was strong enough for practical application.

All-wet fabrication technology for high aspect ratio TSV using electroless barrier and seed layers

All-wet fabrication process using electroless deposition of barrier and Cu seed layers has been achieved for a high aspect ratio through-Si via (TSV). Formation of thin barrier metal layer of NiB and CoB is possible by the use of nano particles catalyst which is densely adsorbed on SiO2 of TSV sidewall. Silane coupling agent with 3-aminopropyl-triethoxysilane is effective for enhancement of adsorption density of nanoparticles. Conformal electroless Cu layer is deposited on the barrier layer without catalyst by bdisplacement plating. The adhesion strength between electroless barrier layer and SiO2 substrate is strengthed by annealing. These results strongly suggest a possibility of the all-wet process for high aspect ratio TSV.