Unit processes for Cu/BCB redistribution layer bonding for 3D ICs

• A novel via-first, back-end-of-the-line (BEOL) compatible, monolithic wafer-level three-dimensional (3D) interconnect technology platform is presented. This platform employs wafer bonding of damascene-patterned metal/adhesive redistribution layers on two wafers to provide both high density of inter-wafer electrical interconnects and strong adhesive bond of two wafers in a single unit processing step. Two key steps for this approach are 1) fabrication of a metal/adhesive redistribution layer on the BEOLprocessed wafers by damascene patterning and 2) face-to-face alignment and bonding of two wafers utilizing copper/tantalum (Cu/Ta) and benzocyclobutene (BCB) redistribution layers. A baseline process and two modified processes are investigated toward evaluation of 1) acceptable wafer-scale nonplanarity, removal rate, and surface damage after CMP and 2) seamless bonding at all three possible interfaces with sufficiently strong BCB-to-BCB critical adhesion energy and Cu-to-Cu contact resistance. Migration of voids in the sputtered copper during bonding and etch profiles for different etch processes are discussed.

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