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In this study, we report on the processing and the electrical characterization of a 3D-WLP TSV flow, using a polymer-isolated, Cu-filled TSV, realized on thinned wafers bonded to temporary carriers. A Cu/Sn microbump structure is integrated in the TSV process flow and used for realizing a two-die stack. Before TSV processing, the Si wafers are bonded to temporary carriers and thinned down to 50 mum. The actual TSV and microbump process uses 3 masks, two Si-DRIE steps and a polymer liner as a dielectric. The dimensions of the TSV structure are: 35 mum Oslash TSV, 5 mum thick polymer liner, 25 mum Oslash Cu, 50 mum deep TSV, and a 60 mum TSV pitch.