Wafer-Level Low-Temperature Solid-Liquid Inter-Diffusion Bonding With Thin Au-Sn Layers for MEMS Encapsulation

Abstract

A novel solid-liquid inter-diffusion (SLID) bonding process is developed allowing to use thin layers of the Au-Sn material in wafer-level microelectromechanical systems (MEMS) packaging while providing a good bonding strength. The bond material layers are designed to have a robust bond material configuration and a metallic bond with a high re-melting temperature, which is an important advantage of SLID bonding or with its alternative name, transient liquid phase (TLP) bonding. The liquid phase in SLID bonding is the gold-rich eutectic liquid of the Au-Sn material system, where the bonding temperature is selected to be 320 • C for a reliable bonding. The average shear strength of the bonds is measured to be 38±1.8 MPa. The hermeticity of the package is tested with the He-Leak test according to MIL-STD 883, which yields a leak value lower than 0.1 × 10 −9 at m.cm 3 /s. The vacuum inside the package without a getter is calculated as 2.5 mbar after cap wafer thinning. The vacuum level is well preserved after post-processes such as annealing at 400 • C and the dicing process. These results verify that thin layers of Au-Sn materials can be used reliably with the SLID or TLP bonding technique using the new approach proposed in this study.

Influence of Barrier Layers on ZrCoCe Getter Film Performance

“…Microelectromechanical system (MEMS) devices have been used in aerospace [ 1 ], biomedical [ 2 ], automotive [ 3 ], communications [ 4 ], as well as other high-tech fields [ 5 , 6 ], many of which use Ge as a substrate [ 7 , 8 , 9 ]. Getter films have attracted significant attention for their sorption performance in maintaining and improving the vacuum degree in MEMS vacuum devices for extended periods [ 10 , 11 , 12 , 13 ]. Vacuum package and long-term reliability are important in MEMS gyroscopes to ensure their detection accuracy [ 12 , 14 , 15 ].…”

“…Getter films have attracted significant attention for their sorption performance in maintaining and improving the vacuum degree in MEMS vacuum devices for extended periods [ 10 , 11 , 12 , 13 ]. Vacuum package and long-term reliability are important in MEMS gyroscopes to ensure their detection accuracy [ 12 , 14 , 15 ]. The vacuum encapsulation can provide a high-quality factor and reduce noise interference in MEMS accelerators [ 16 ].…”

A Method for Fast Au-Sn Bonding at Low Temperature Using Thermal Gradient

“…Traditionally, the Au-Sn eutectic bonding process proceeds at the temperature range of 280 • C-350 • C [14,15], involving solid-liquid diffusion bonding or instantaneous liquidphase bonding. However, this method carries the risk of Sn extrusion, leading to potential short-circuits [16,17].…”

Microstructural and Mechanical Characterization of Cu/Sn Slid Bonding Utilizing Co as Contact Metallization Layer

“…Many MEMS devices require a hermetic packaging with preferably no postprocessing after the MEMS device is released [1][2][3]. In addition, for some MEMS devices (e.g., CMOS-MEMS devices), it is crucial to limit the heat load on the wafers [4]. In this regard, solid-liquid interdiffusion (SLID) bonding is an attractive process for MEMS packaging due to its high hermeticity, low bonding temperature, and high re-melting temperature [4,5].…”

“…In addition, for some MEMS devices (e.g., CMOS-MEMS devices), it is crucial to limit the heat load on the wafers [4]. In this regard, solid-liquid interdiffusion (SLID) bonding is an attractive process for MEMS packaging due to its high hermeticity, low bonding temperature, and high re-melting temperature [4,5]. However, as most MEMS devices contain fragile parts and operate in harsh environments -which bring wider variety of failure mechanisms compared to traditional semiconductor microelectronics -the reliability of SLID bonding and complete interconnection materials require evaluation.…”