Study of Cross-Contamination in Multi-Chamber PVD Systems Used for High-Throughput Seed Layer Deposition

The increasingly higher interconnect density in modern WLP applications exponentially increases the importance of the interconnects quality as the critical dimensions shrink. The metric defining the quality of the interconnects is the contact resistance, Rc. UBM and RDL metallization are key fabrication steps that provide the routing between the I/O pads of the chip and the bumps. In high-volume manufacturing, the adhesion and seed layers necessary to fabricate UBM and RDL are deposited in multi-chamber PVD systems. Two industry standards are available: the Indexer and the Cluster type. In previous research, we reported on the performance of the Indexer delivering 50% lower Rc and 40% higher throughput compared to the Cluster counterpart. The novel aspect of this research is the investigation of the cross-contamination occurring in these competing platforms. RGA measurement is performed to study the propagation of the residual outgassing through the PVD systems during continuous run. SiO2 wafers are used as reference due to their negligible outgassing and compared to PBO coated wafers mimicking the outgassing of typical products with organic passivation. Experimental data has shown that the main source of contamination in both platforms is the residual outgassing of the etched PBO wafer being transported from one chamber to the next. In contrast, the cross-talk between chambers is marginal. Moreover, the faster chamber-to-chamber transfer time in the Indexer mitigates the risk of recontamination of the cleaned I/O contacts.