In this paper, we report on the processing and the electrical characterization of a 3-D-wafer level packaging through-silicon-via (TSV) flow, using a polymer-isolated, Cu-filled TSV, realized on thinned wafers bonded to temporary carriers. A Cu/Sn micro-bump 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 μm. The actual TSV and micro-bump process uses 3 masks, two Si-deep-reactive ion etching steps and a polymer liner as a dielectric. The dimensions of the TSV structure are: 35 μm ^ØTSV, 5 μm thick polymer liner, 25-μm-Ø Cu TSV, 50 μm deep TSV, and a 60 μm TSV pitch.

Irreversible extrusion of Cu from through-silicon vias (TSVs) during high-temperature processing steps presents an important potential back-end-of-line (BEOL) reliability issue. Commonly this reliability risk is mitigated by introducing an anneal after Cu plating for TSV fill. This paper presents the impact of the post-plating anneal temperature and time on residual Cu pumping during a sinter for 20 min at 420 °C, for two different TSV dimensions. Using optical profilometry, in total ~ 4000 TSVs were measured, allowing detailed statistical analysis. Within one sample the Cu pumping values were found to be log normally distributed, implying an intrinsically large spread. Lower residual Cu pumping values were found in TSVs annealed at higher temperatures and for longer times, with the sinter conditions of 20 min at 420 °C confirmed as optimal post-plating anneal conditions. The larger TSVs showed more pumping in the average TSV, but at the tail of the distribution the Cu pumping behavior was the same as for the smaller TSVs. This implies that the impact of Cu pumping on BEOL reliability is identical for both sets of TSV dimensions, suggesting that the impact of Cu pumping on BEOL reliability is not necessarily reduced by reducing TSV dimensions.

This work focuses on using copper (Cu) as the main conductor as an alternative to standard screen printed silver (Ag) front contacts for homogeneous emitter silicon solar cells.Two different approaches to form Cu plated contacts based on laser ablation of the SiNx:H antireflection coating (ARC) and subsequent plating steps are presented. In the first approach, contacts are formed by Ni/Cu/Ag plating in an industrial in-line plating tool and subsequent rapid thermal annealing (RTA). In the second approach, the RTA step is performed after sputtering of a thin nickel layer and prior to the final Ni/Cu/Ag plating sequence. Using the latter approach, results are presented on large area 12.5×12.5 cm2 p-type CZ-Si PERC-type solar cells featuring an advanced 120Ω/sq homogeneous emitter and local Al contacts on the rear surface accompanied by a SiOx/SiNx rear side passivation stack. Solar cell efficiencies of up to η=19.6% and average pull tab adhesion results >2N are reported