In this article, a self-assembled monolayer (SAM) is applied onto the copper surface in an attempt to lower the required bonding temperature. Alkane-thiol with 6-carbon chain length is used and tested for bonding experiment. The adsorption of SAM is confirmed by the sharp rise of the water contact angle measurement and the reduced in the surface roughness. Next, the desorption of SAM is done at a high temperature anneal (<300°C) in an inert ambient and its properties are characterized by the water contact angle measurement and XPS. It is found that the water contact angle measurement decreases sharply close back to the contact angle of the pure blanket copper surface after annealing of SAM. The XPS results also show the ability of SAM in protecting Copper surface from oxidation. Finally, shear test is performed on Cu-Cu structures bonded at low temperature (250°C) in order to verify the SAM behavior in protecting the copper surface from oxidation and enhancement for bonding. The wafer pairs with and without SAM are intentionally exposed in clean room environment for few days. The bonded pieces are diced and subject to shear stress and results show that with SAM protection, shear strength is improved due to the enhancement in grain growth as a result of cleaner surface.

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