Y. N. Hua, GLOBALFOUNDRIES Singapore Pte Ltd, Singapore, Singapore; S. P. Zhao, Chartered Semiconductor Mfg Ltd., Singapore, Singapore

Summary: Galvanic corrosion may result in discolored or non-stick bondpad problem. In authors’ previous studies [Hua et al, ISTFA 1998 and ISTFA 2000], theory, characteristics and eliminating solutions of galvanic corrosion have been discussed. It is well-known that after wafer-die sawing process, sometime Si dust is difficult to be cleaned away by DI water, especially at pinhole/corrosive areas caused by galvanic corrosion, thus resulting in NSOP at the assembly houses. It is also noted that Si dust has made significant contribution to NSOP. However, till now, the mechanism is not fully understood and there isn’t a suitable theory to explain it. To eliminate NSOP due to Si dust, it is necessary to further study the mechanism. In this paper, we will study the mechanism of Si dust contamination, and propose the concept of Si dust corrosion. After studying, a theoretical model will be introduced so as to explain Si dust contamination problem during wafer die sawing process, and then discuss the eliminating methods of Si dust on microchip Al bondpads during wafer-die sawing process. After studying, we propose the below mechanism: DI H2O related process enhances galvanic corrosion -> Generate new corrosive product [OH]- ions -> [OH]- causes Si dust corrosion -> Form Si Gel-like materials (nSiO2.nH2O) -> NSOP Based on the above mechanism model, we think that if galvanic corrosion occurs on Al bondpads during wafer die-sawing process, [OH]- ions generated from galvanic corrosion will not only react with Al to cause Al corrosion (form Al (OH)3), but also react with Si dust to cause Si dust corrosion. During Si dust corrosion, poly-H2SiO3 and Si-Al-O complex compounds will be formed on Al bondpads at the corrosive areas. During Si duct corrosion, Si dust becomes a “Gel-like” material that has a high level of stickiness and will stick onto the surface of bondpads. “Gel-like” material is insoluble in water and difficult to be cleaned away by DI water during or after wafer die-sawing processes. In this paper, an electrochemical theoretical model (chemical equations) will be presented, which will help us to understand the mechanism of Si dust contamination and Si dust corrosion during wafer die-sawing process so as to find a solution to reduce Si dust on Al bondpads and eliminate NSOP during the assembly processes. TOF-SIMS technique is employed to identify the compounds of Si-O and Si-O-Al and study the mechanism of Si dust corrosion physically and chemically. The eliminating methods of Si dust on microchip Al bondpads during wafer-die sawing process will be introduced and discussed.