Fig. 6: Complete fabrication flow for the ultra-deep TSV technique and the step-by-step fabrication results

a Proposed fabrication flow: (I) etching of ultra-deep blind vias by DRIE, (II) deposition of PI liner by the vacuum-assisted spin-coating technique, (III) formation of Ni barrier/seed layer by the proposed dual catalysis-based ELP technique, (IV) electroplating of Cu annular conductors, (V) filling of BCB into the vias under vacuum treatment, and (VI) fabrication of RDLs. b–e SEM images of the fabrication results after the formation of PI liners, Ni barrier/seed layers, Cu annular conductors, and BCB fillers, respectively. Notably, the fillers in c and d are resin that is necessary for metallographic polishing, and the filler in e is BCB