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0968-V02-06

Reactive Multilayer Foils for Silicon Wafer Bonding Xiaotun Qiu and Jiaping Wang Department of Mechanical Engineerring, Louisiana State University, Baton Rouge, LA, 70803 ABSTRACT In this study silicon wafers were bonded using Al/Ni reactive multilayer foils as local heat sources for melting solder layers. Exothermic reactions in Al/Ni reactive multilayer foils were investigated by XRD and DSC. XRD measurements showed that dominant product after exothermic reaction was ordered B2 AlNi compound. The heat of reaction was calculated to be 57.9 KJ/mol by DSC. With Al/Ni reactive multilayer foil, localized heating can be achieved during bonding process. Both experimental measurements and numerical simulation showed that the heat exposure to the wafers was highly limited and localized. Moreover, leakage test showed that this bonding approach possessed a good hermeticity. INTRODUCTION Wafer bonding techniques, such as anodic bonding and fusion bonding, have been reported for the silicon wafer-to-wafer bonding processes [1]. However, these bonding techniques are conducted at high temperature, 1000°C for the conventional fusion bonding and 300-500°C for anodic bonding. These high temperature processes may cause thermal damage to components. Dissimilar materials may debond on cooling due to the CTE (coefficient of thermal expansion) mismatch. Another disadvantage of these processes is that they require the bonding surfaces to be polished and thoroughly cleaned to achieve uniform bonding. Instead of bonding wafers directly, intermediate layer bonding methods, which employ thin films on one or both component surfaces as the bonding media, can be used to lower the bonding temperature. Intermediate layer bonding methods such as solder bonding and adhesive bonding also have their own shortcomings: the out-gassing of the flux and solvent in the solder paste during solder reflow can form voids in the bonding area [2], while the disadvantages of adhesive bonding are long-term instability, a limited working temperature range, low bonding strength, and nonhermeticity of the package [3]. In this regard, a special low temperature wafer bonding technique needs to be further researched for various wafer level packaging applications. In this paper, we describe a novel room temperature bonding technique using reactive multilayer Al/Ni foils as local heat sources to melt solder layers and thus bond silicon wafers. Reactive multilayer foils contain hundreds of nanoscale Al and Ni bilayers. Self-propagating formation reactions in such foils are driven by a reduction in chemical bond energy. This local reduction of chemical bond energy produces a large quantity of heat that is conducted down the foil and facilitates more atomic mixing and compound formation. Self-propagating reactions can be ignited in these foils at room temperature with a small thermal pulse. Such reactions in multilayer foils can be used as local heat sources to melt solders or brazes and thus bond components in a variety of applications [4-8]. With localized hea