Study on low temperature indium based solder for 3D integrated circuits application

Due to limitations of the conventional 2-dimensional integrated circuit (IC) layout, the electronics industry has shifted its research focus towards 3-dimensional (3D) ICs design to overcome such future problems. A common 3D ICs architecture that has been proposed involves the stacking of multiple chips that are bonded inter-facially using solders at low temperatures and pressure. As recent international regulations have prohibited the use of established lead based solder technology (which is toxic), a suitable replacement solder material needs to be found. The purpose of this study is to investigate the viability of an Indium-based solder alloy for 3D IC chip stacking and bonding purpose. In this study, 75In25Sn solder is bonded at 1.9MPa while the bonding and annealing temperature and varied in the range between room temperature to 200°C. From the results obtained, the bonding mechanism is proposed. Bonding at higher temperatures would result in higher true contact area between the solder and the copper surface. Through annealing at higher temperatures, inter-metallic compounds (IMC) would form from these contact sites. To understand the kinetics of IMC formation, a simple in-situ experiment was carried out using solder and copper layers that were sputtered onto a glass slide. The proposed experiment hopes to reduce the time required by conventional study methods. However, further work is required as the final results achieved were not within expected theoretical data. This study concludes that indium based alloy is a suitable candidate as a solder material for 3D ICs. Its low melting point and ability for good IMC formation allows for bonding at low pressure and temperatures. Further studies could be done to understand the impact of varying bonding pressure and other composition ratios.Bachelor of Engineering (Materials Engineering