Investigation on bond strength and contact resistance of copper-copper bonds for 3D integrated circuits

Advancement of the current Two-Dimensional integrated circuits (2D-ICs) is limited by increasing interconnect delay and huge power dissipation problem. Hence, Three-Dimensional integrated circuits (3D-ICs) technology, in which active layers are stacked vertically and linked by short vertical interlayer interconnects, is an emerging solution as not only does it effectively overcome limitations of the 2D-ICs technology by reducing interconnects length, it also allows the heterogeneous integration of different technologies. Metal-to-metal bonding, in particular copper-copper bonding, is an attractive technology for fabricating 3D-ICs because of its dual function of electrical connection and mechanical link between the active layers. And copper is chosen for its good electrical and thermal conductivities, and high electro-migration resistance. In this report, copper-copper thermo-compression is used as the bonding technology whereby compressive force and heat are simultaneously applied to bring two otherwise separated copper surfaces together. Mating surfaces‟ cleanliness, bonding temperature, applied load, duration and environment need to be optimized so as to achieve high quality bond. Other than these factors, film thickness is predicted to be one of the contributing factors to bond integrity. Hence investigation on its effect is carried out by bonding samples with varying film thickness. Experimental results however, do not validate the suggested direct correlation between film thickness and bond quality.Bachelor of Engineering (Materials Engineering