Study on kinetics of IMC formation through simple in-situ experiments for 3D IC applications

• Main Author: Foo, Jie Sheng.
• Other Authors: Gan Chee Lip
• Format: Final Year Project
• Language: English
• Published: 2011
• Subjects: DRNTU::Engineering::Materials
• Online Access: http://hdl.handle.net/10356/44574
• Institution: Nanyang Technological University

One of the challenges in realization of 3D IC is the requirement of having low processing temperatures. In order to overcome such challenges, researches have been conducted in an attempt to lower down the bonding temperature. One such way would be through the usage of low temperature solders such as In-Sn based solder. The understanding of the kinetics of the solder with Cu is important especially for the process, performance and reliability of the bonding. From the other studies done, the kinetics of In-Sn with Cu at thin film scale is still not well understood, which includes the effect of In-Sn composition, effect of the thickness of the Cu layer and determining the rate limiting factor. The purpose of this project is to study the role played by In-Sn composition and thickness of the Cu layer in the formation of the ŋ phase (intermetallic compound) IMC, Cu6(Sn,In)5. In this project, bilayer of Cu and solder was annealed to study the growth mechanism of the IMC. The solders used were of composition In-25%Sn and In-50%Sn of 700-1000 nm thick, while the Cu thicknesses of approximately 171 nm, 211 nm and 287 nm were deposited on glass substrates prior to deposition of the solder through E-beam deposition. The thicknesses were chosen to ensure than only the ŋ phase IMC would form. The Ea calculated in this experiment for the formation of the ŋ phase IMC, Cu6(Sn,In)5 is in the range of 24.6 – 47.6 kJ/mol which is comparable to some previous studies. The rate limiting factor is assumed to be due to the diffusion of Cu atoms across the ŋ phase IMC through comparison with literature done on Cu6(Sn,In)5 and Cu6Sn5 formation. The increased thickness of the Cu seems to cause Ea to increase, which may suggest a change of rate limiting factor. Effects of increasing In composition also suggested faster formation of the IMC. Further studies need to be done on more composition of In-Sn based solder to determine the effect Indium has on the IMC formation. The in-situ study has been found to be effective in understanding the kinetics of formation of the IMC.