We explore a methodology for patterned copper nanoparticle paste for 3D interconnect applications in wafer to wafer (W2W) bonding. A novel fine pitch thermal compression bonding process (sintering) with coated copper nanoparticle paste was developed. Most of the particle size is between 10-30 nm. Lithographically defined stencil printing using photoresist and lift-off was used to apply and pattern the paste. Variations in sintering process parameters, such as: pressure, geometry and ambient atmosphere, were studied. Compared to Sn-Ag-Cu (SAC) microsolder bumps, we achieved better interconnect resistivity after sintering at 260 °C for 10 min, in a 700 mBar hydrogen forming gas (H2/N2) environment. The electrical resistivity was 7.84 ± 1.45 μΩ·cm, which is about 4.6 times that of bulk copper. In addition, metallic nanoparticle interconnect porosity can influence the electrical properties of the interconnect. Consequently, we investigated the porosity effect on conductivity using finite element simulation. A linear relationship between the equivalent conductivity and particle overlapping ratio was found.@en

We explored the properties and performance of copper-based metallic nanoparticle paste (MNPs) for interconnects applications in 3D heterogeneous integration. A patterning method was developed to process micron sized sintered MNPs structures. This enables the fabrication of IC interconnect test structures to characterise specific resistivity sintered MNPs and the contact resistances of sintered MNP to bulk copper (bCu) which was respectively 78.4 mOhm.micrometer and 0.23 Ohm.micrometer2. In situ XRD analysis showed no oxidation of MNPs at processing temperatures below 100 °C. When Copper based MNPs are sintered under forming gas conditions, no oxidation of copper is measured. With in situ TEM at a temperature range of 220 - 260 oC local melting of copper nanoparticles was observed. This is in agreement with the electrical measurements, the resistivity and contact resistance are considerably reduced when MNPs is sintered in this temperature range. Copper-based MNPs is successfully applied as die attach and wafer to wafer (W2W) bonding. However, for W2W bonding, the specific contact resistance was 800 Ohm.micrometer2.@en