Wafer Bonding Technologies for Microelectromechanical Systems and 3D ICs: Advances, Challenges, and Trends

Wafer bonding is the process to permanently connect two or more wafers for three-dimensional (3D) integration in microelectromechanical systems (MEMS) and the semiconductor industry. This review compares existing bonding technologies based on wafer preparation, external activation, and bonding mechanisms. These technologies are divided into two main categories: direct bonding and indirect bonding. Direct bonding has no intermediate layers, including surface activated bonding (SAB) and anodic bonding. Indirect bonding has intermediate layers, for example, metallic bonding uses metals of copper (Cu), gold (Au), and eutectic alloys; adhesive bonding uses polymers and solder. Recent advancements over the past decade are explored, including the applications in 3D integrated circuit (IC) and packaging, as well as state-of-the-art molecular modelling in the wafer bonding research. The review highlights key challenges and emerging trends across various wafer bonding technologies, emphasizing the importance of material selection in wafer preparation, bonding strength, and cost-effectiveness. The study analyses factors like surface roughness, cleaning, temperature, pressure, voltage, and thermal expansion tolerance to guide informed decisions in bonding technology. By offering comprehensive insights into technical details, costs and applications, this review work empowers researchers and device manufacturers to grasp the nuances of wafer bonding technology, its evolution, and make informed decisions.