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

Abstract

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.