Method to Reduce Crystal Defects in AlCu Bond Pad

AlCu bond pad crystal defect is observed after wafer processing and before die sawing. It affects wire bonding or bump performance resulting in lower bond pull and ball shear force, even adhesion failure. There are many factors contributing to the crystal defect, such as: polymer removal status, storage condition, humidity and fluorine concentration in the environment etc. Up to date, the impact of humidity and fluorine concentration to crystal defect has been broadly studied, but the polymer remover's effect is somewhat unknown. In this paper, two different chemistry based polymer removers are studied to correlate to crystal defect behavior. After processed by the polymer remover, AlCu bond pad wafers are subject to different environment conditions including wet box (44% and 63% humidity separately). Subsequently, each wet box is filled with fluorine at the concentration of 524ug/pod. The crystal defect growth is examined as a function of time using optical methodology. The results reveal that the polymer chemistry is also critical to crystal defect growth as well as the impact on queue time and storage conditions. An optimized fluoride containing polymer remover can substantially lower the crystal defect risk leading to a wider process windows.