Preconditioning Technologies for Sputtered Seed Layers in FOPLP

The shift from Fan-Out Wafer Level Packaging (FOWLP) towards Fan-Out Panel Level Packaging (FOPLP) is mainly driven by the expected cost reduction. While the same quality as in FOWLP is requested however, larger, more flexible substrates based on mold compound causing heavy outgassing need to be handled successfully. The main quality criteria for a sputtered seed layer in packaging are adhesion, contact resistance (RC) and yield (particles and other substrate damages). Reliable substrate handling and good process uniformities are however the key enablers a hardware and process supplier needs to guarantee to enter the FOPLP market. In this paper we focus on the influence of preconditioning technologies, namely degassing and physical etching, on contact resistance. Degassing technologies are compared and a newly developed dual frequency capacitive coupled plasma (DF CCP) etch source with a dual electrode is tested. This DF CCP source combines the good characteristics of different etching technologies, offering an optimized solution for panel preconditioning. Experiments were performed on a fully automated panel level production tool with cluster architecture. RC devices with Aluminum and Copper contact pad materials were tested, having pad sizes of 5 - 30 um. The influence of process variations on the RC was tested and the data compared with residual gas analysis measurements to explain process performance results. The results enabled the definition of design criteria for preconditioning technologies. Experiments were run in parallel on a state of the art FOWLP tool confirming no relative reduction in performance for panel processing and therefore paving the way for FOPLP.