Temperature Effect on Intermetallic Compound Growth Kinetics of Cu Pillar/Sn Bumps

Abstract

The in situ intermetallic compound (IMC) growth in Cu pillar/Sn bumps was investigated by isothermal annealing at 120°C, 150°C, and 180°C using an in situ scanning electron microscope. Only the Cu 6 Sn 5 phase formed at the interface between the Cu pillar and Sn during the reflow process. The Cu 3 Sn phase formed and grew at the interfaces between the Cu pillar and Cu 6 Sn 5 with increased annealing time. Total (Cu 6 Sn 5 + Cu 3 Sn) IMC thickness increased linearly with the square root of annealing time. The growth slopes of total IMC decreased after 240 h at 150°C and 60 h at 180°C, due to the fact that the Cu 6 Sn 5 phase transforms to the Cu 3 Sn phase when all of the remaining Sn phase in the Cu pillar bump is completely exhausted. The complete consumption time of the Sn phase at 180°C was shorter than that at 150°C. The apparent activation energy for total IMC growth was determined to be 0.57 eV.

Optimized Cu-Sn Wafer-Level Bonding Using Intermetallic Phase Characterization

“…This differs from earlier published work, which considered IMC formation to be fully diffusion controlled, [18][19][20][21][22] with an analytical solution of the diffusion equation of n = 1/2. However, several studies have presented values of n that vary with temperature.…”

Phase transformation and fracture behavior of Cu/In/Cu joints formed by solid–liquid interdiffusion bonding

“…Currently, the research activities of Cu-In system mainly focus on Cu-In intermetallic compounds theoretical analysis and their growth kinetics [14][15][16][17]. However, there is a lack of systematic study on microstructure evolution of Cu/In/Cu joints under different bonding conditions.…”

Interfacial Reaction Effect on Electrical Reliability of Cu Pillar/Sn Bumps

“…6,7,18 Cu 3 Sn layers on both interfaces grew to similar thickness. The growth rate of Cu 3 Sn in Cu pillar/Sn bumps was also faster than that of Cu 6 Sn 5 due to the Sn-limited nature of the Cu-Sn reaction system, 11,19 while in a conventional solder bump the Cu-Sn reaction system is Cu limited. The Sn phase was not observed at the Cu pillar/Sn interface after 165 h at 150°C or after 100 h at 150°C, 3.5 9 10 4 A/cm 2 ; on the other hand, the Sn phase was still observed at the Cu pillar/Sn interface after 360 h at 100°C.…”

“…Similar results are reported elsewhere. [11][12][13] Kirkendall voids were observed at the Cu/Cu 3 Sn interface as well as within the Cu 3 Sn layer. It has been reported that the Kirkendall void formation mechanism can be ascribed to the different diffusivities of Cu and Sn.…”

“…Similar experimental methods are reported in detail elsewhere. [9][10][11][12] The evolution of each interfacial microstructure and the IMC growth in the Cu pillar/Sn bumps was analyzed using SEM in backscattered electron (BSE) mode and using energy-dispersive x-ray spectroscopy (EDS). IMC thickness was measured from the IMC layers at both the chip and substrate sides.…”