Studies of Fluorine-Induced Corrosion and Defects on Microchip Al Bondpads and Elimination Solutions

Abstract In this paper, a comprehensive study of Fluorine-induced Aluminum bondpad corrosion will be presented. Fluorine corrosion is detrimental to Al pad quality resulting in non-stick on pad (NSOP). In wafer fabrication, NSOP refers to lift-off of Au wire-bond from the surface of Al bondpad due to its poor adhesion to the contaminated pad surface. It will be shown that besides the well-known corrosion mechanism that causes NSOP, namely, via the formation of Al fluoride defect ([AlFx](x-3)-), it can also happen due to Al fluoride oxide defect, AlxOyFz. Unlike the Al fluoride defect, which has a unique “flower-like” shape, Al fluoride oxide defects exist in a variety of shapes: “Crystal-like”, “Oxide-like” and “Cloud-like”. The physical dimensions of these defects (including Al fluoride) can be dramatically different, varying all the way from micron to nanometer. In this paper, each of these morphological shapes and their respective failure mechanisms will be covered. Solutions to mitigate F-corrosion and ways to control/monitor contamination on Al pad surface in wafer fab will be presented.