A novel process of fabricating anchored three dimensional (3D) micron scale structures using solder based self assembly (SBSA) method is developed in the laboratory. The prototype of solder filled 3D structures are currently fabricated as interposts on the simulated metallled through silicon vias (TSVs), applicable for 3D integrated circuit (IC) stacking. Two types of soldering, face-soldering and edge-soldering, were studied to fabricate 3D structures. Face-soldering refers to the deposition of solder on the complete metal face whereas edge-soldering refers to selective deposition of solder on the edges of the metal face. Solder is deposited on adjacent metallic faces of 2D patterns, bridging the small gaps between individual faces. When all but one face of a 2D patterns are freed from the substrate and solder is reheated to a liquid state (refow), the untethered faces of the pattern fold upwards, out of the plane, to form the desired 3D structures. Both types of soldering are completed using a robust dip soldering process. Dip soldering at a certain temperature and dip time are needed to obtain the desired structures. Face-soldered 3D structures provide a solder stando height that serves as a connection paths in the integration of dissimilar electronic technologies. The SBSA structure provides variety in size and shape with the potential to also serve as a reservoir for solder to aid in chip bonding. The solder standoff height obtained in the 3D structures remained heat resistant and demonstrated uniform thicknesses across a large array of SBSA structures. The solder stando height was further validated using a popular open source simulation tool, Surface Evolver. The electrical durability of SBSA posts were determined by completing current-voltage (I-V) measurements on interconnected 3D structures after thermal treatments. Fabricated SBSA posts were subjected to thermal cycling with temperatures ranging from room temperature to 300 C. The 3D structures are shown to be stable until 165 C with little variation in measured resistance. Further damascene and embossed metal structures are patterned on the sides of 3D micro-scale structures to demonstrate a viable 3D patterning technique for future IC fabrication. Readers are encouraged to view a video on the formation of self assembled 3D structures from the video clip: http://unix.eng.ua.edu/~mrrao/trsqpyHiDef.wmv
Madhav Rao received his Bachelor of Engineering in Electronics and Telecommunication from the Mumbai University in 2004. In the final year of Engineering, he secured 13th rank in the Mumbai University. He worked in Larsen and Toubro-Embedded systems in Mysore, Karnataka from July-2004 to June-2006. He was awarded the Master of Science degree in Microelectronics from the University of Arkansas, USA, in December-2007. In his Masters thesis, he investigated setting logical inputs to an edge driven computational device consisting of magnetic nickel nanodots of size ranging 200 nm to 500 nm. From 2008 onwards, he was working on developing 3D structures on silicon chip using a novel self assembly method in the University of Alabama, USA. He defended his Ph.D dissertation and was awarded the Ph.D degree in Electrical Engineering in May, 2012. Currently he is working in IIIT-Bangalore as Assistant Professor. He has published multiple journal articles related to the research. Besides this, he has research interests in developing carbon-nanotubes in through silicon vias (TSVs) to improve the thermal and electri- cal properties of vertical interconnects in VLSI circuits. He is also associated in developing text based software audio lters and simple-and-ready to use robot programming. He has educational publications on the same. In 2009, he along with other graduate and undergraduate students received a grant of $10,000 from NASA and Alabama Space Grant Consortium, USA to build a telerobotic system consisting of two independent robots, which was demonstrated in Lunabot excavation challenge in Kennedy space center, NASA, Florida in May, 2010. Madhav Rao enjoys teaching and likes tointegrate research in teaching. He has taught Introduction to Programming to freshman students in the University of Alabama in Fall 2009 and Fall 2010. He is currently teaching Programming and basic electronics in IIIT-Bangalore.