ABSTRACT
This article presents a novel bonding method for chip packaging applications in the semiconductor industry, with a focus on downsizing high-density and 3D-stacked interconnections to improve efficiency and performance. Microfluidic electroless interconnections have been identified as a potential solution for bonding pillar joints at low temperatures and pressures. However, the complex and time-consuming nature of their production process hinders their suitability for mass production. To overcome these challenges, we propose a tailored plating solution using an enhanced copper concentration and plating rate. By eliminating the need for fluid motion and reducing the process time, this method can be used for mass production. The Taguchi approach is first used to optimize the copper-quadrol complex solution with the plating rate and decomposition time. This solution exhibits a copper concentration that is over five times higher than that of conventional solutions, a plating rate of 22.2 µm/h, and a decomposition time of 8 min on a Cu layer substrate. This technique enables Cu pillars to be successfully bonded within 7 min at 35 °C. Planarizing the pillar surface yields a high bonding percentage of 99%. Mechanical shear testing shows a significant fracture strength of 76 MPa.
ABSTRACT
Cu-to-Cu direct bonding plays an important role in three-dimensional integrated circuits (3D IC). However, the bonding process always requires high temperature, high pressure, and a high degree of consistency in height. In this study, Sn is passivated over electroplated copper. Because Sn is a soft material and has a low melting point, a successful bond can be achieved under low temperature and low pressure (1 MPa) without any planarization process. In this experiment, Sn thickness, bonding temperature, and bonding pressure are variables. Three values of thicknesses of Sn, i.e., 1 µm, 800 nm, and 600 nm were used to calculate the minimum value of Sn thickness required to compensate for the height difference. Additionally, the bonding process was conducted at two temperatures, 220 °C and 250 °C, and their optimized parameters with required pressure were found. Moreover, the optimized parameters after the Cu planarization were also investigated, and it was observed that the bonding can succeed under severe conditions as well. Finally, transmission electron microscopy (TEM) was used to observe the adhesion property between different metals and intermetallic compounds (IMCs).
