Low-Temperature Direct Bonding of 3D-IC Packages and Power IC Modules Using Ag Nanotwinned Thin Films

Ag has the lowest stacking fault energy of all metals, which allows twin formation to occur more easily. The (111)-preferred orientation Ag nanotwinned films is fabricated by either sputtering or evaporation method exhibit columnar Ag grains grown vertically on Si substrates. Ag nanotwinned films have a (111)-preferred orientation with a density about 98% and diffusivity that is 2 to 5 orders of magnitude higher than those of (100) and (110) surfaces. Low temperature direct bonding with (111)-oriented Ag nanotwins films is proposed to fulfil the requirements for wafer-on-wafer (WoW), chip-on-wafer (CoW), and chip-on-wafer-on-substrate (CoWoS) advanced 3D-IC packaging, with the process temperature drastically reduced to 100°C. Such an innovative bonding method also provides a promising solution for die attachment of Si chips with DBC-ceramic substrates for power module packaging.