Study of Interface Micro-Voids Between Sputter Cu & Plating Cu: The Role of Photoresist

In microelectronic packaging industry, solder joints are used to form an electrical and mechanical connection, which can be viewed as a kind of "Electrical Glue" between package elements. The integrity of solder joints plays an important role in the reliability of the end-use electronic products. Any interface micro-voids existed in two neighbored layers will undoubtedly degrade the robustness of a solder joint and raise serious reliability concerns. The formation of these Cu/Cu micro-voids at interface will weaken the bonded interface, and easily leading to brittle interfacial fracture when the solder interconnects is subjected to an unexpected shear or pull stress, thus, the study of micro-voids formation and the approach to resolve it become more and more significant. Thus, the objective of this study will focus and emphasize on exploring one of the suspected factors to cause Cu/Cu interface micro-voids formation: "Photoresist", and the way to lower even eliminate the unwelcome Cu/Cu micro-voids defect. Since both positive and negative acting type photoresist have their own advantages as well as applications in current technology, we will use negative photoresist as control group and take positive photoresist as test condition to explore the role of "Photoresist" on the formation of Cu/Cu micro-voids under same experimental conditions in the present study. Experiment results and the promising improvement actions for reducing Cu/Cu micro-voids will be discussed and studied step-by-step in detail as well in this paper.