Comprehensive defect monitoring technique for advanced fanout packaging process

With the latest advances in technology nodes becoming very cost-intensive, the semiconductor industry has focused on cost-saving approaches in the packaging space. Fanout packaging is expected to play an increasingly major role in the coming years. While there have been many published articles on the process integration, this paper focusses on yield and reliability in a production environment. The thesis of this paper is a novel approach to yield monitoring because this is critical to a production environment. Latest advances in this technology have resulted in sophisticated fanout packaging processes, such as the multi-chip module fanout packaging, which requires a front-end like approach to defect monitoring and management. As fanout packaging techniques evolve, process complexity and the number of layers are expected to increase significantly compared to the traditional fan-in packaging [1]. Traditionally, before the onset of fanout production, defect monitoring for packaging typically comprised of inspection on the solder bumps. The major source of defects from a packaging perspective are broken, merged or damaged solder bumps. However, fanout packaging uses metal redistribution layers to electrically connect stacks of layers. Moreover, the dimensions of these redistribution layers range around a few microns to tens of microns. The reliability concerns on the redistribution layers are much more severe as opens, shorts and damages on the redistribution layers impact the overall reliability of the packaged chip. Hence, sensitivity or resolution for defects ranging in the order of microns is an important yardstick to measure yield and reliability accurately in the advanced fanout packaging production space. Hence, there is a need to approach defect management in a structured way to accurately estimate yield and defectivity. In this paper, we will discuss and present a comprehensive high throughput, non-invasive, non-contact defect monitoring strategy for state-of-the-art fanout packaged devices with advanced design rules. We would also further discuss different yield killers as seen through our inspection method. This work is a collaborative project between KLA-Tencor and ASE, Kaohsiung.