Y. N. Hua, GLOBALFOUNDRIES Singapore Pte Ltd, Singapore, Singapore; J. Teong, Chartered Semiconductor Manufacturing Ltd, Singapore, Singapore

Summary: In wafer fabrication (fab), CF4 gas is used for Al bondpad opening process. Thus, on a normal Al bondpad, there is a low level of fluorine (F) contamination, which could not cause F-induced corrosion & defects. However, if F contamination is higher than baseline to certain level on Al bondpads, it may cause F-induced corrosion on microchip Al bondpads, which may result in bondpad discoloration or non-stick on pads (NSOP). In authors’ previous studies [Hua et al, ISTFA 2002 and ISTFA 2003], theory, characteristics and eliminating solutions of Fluorine-induced corrosion have been studied. In this paper, we will further study failure mechanism of F-induced corrosion defects on Al bondpads and introduce a concept of Al fluoride oxide (AlxOyFz) defect besides Al fluoride ([AlFx](x-3)-) defect. Theoretical model of Al fluoride oxide (AlxOyFz ) will be proposed to explain chemically & physically mechanism of fluorine-induced corrosion on Al bondpads and three kinds of Al fluoride oxide defects (crystal-like, oxide-like and cloud-like) will be discussed. According to theoretical models proposed in this paper, F will chemically react with Al and form Al fluoride ([AlFx](x-3)-). It is a chemically stable compound and does not dissolve in water. Therefore, once it is formed, it will be difficult to be cleaned away using a normal wafer fab cleaning process. Moreover, O2 & H2O (moisture) will enhance F corrosion and cause chemical reactions to generate OH- ions, which will further chemically react with Al to form Al hydroxide, Al(OH)3 and Al oxide (Al2O3), and then form Al fluoride oxide (AlxOyFz). All these F-induced corrosion defects will cause bondpad discoloration & NSOP problem. In this paper, failure analysis methodologies & eliminating solutions of F-induced corrosion and controlling/monitoring program will be also discussed.