AL to AL wafer bonding for MEMS encapsulation and 3-D interconnect

Abstract

Al to Al bonding was successfully demonstrated for hermetic sealing of MEMS devices and three-dimensional interconnects. On a MEMS device wafer, 2 µm thick Al (with 2% Cu) was patterned at the perimeters of the individual dies as well as the input/output bond pads. On a cap wafer, after forming polycrystalline-Si filled vias, the seal rings and bond pads were also patterned with the Al described above. The two wafers were then bonded at ~ 450 °C with various bond forces up to 80 kN. The leak detection on the capped device showed the superb hermeticity of ~10 -12 cm 3 atm/sec He leak rate with an Al seal width as narrow as 3 µm. And the electrical contact resistance of the Al to Al bonded interface measured less than 1 Ω.

Wafer-Level Vacuum Packaging Enabled by Plastic Deformation and Low-Temperature Welding of Copper Sealing Rings With a Small Footprint

“…• C [22]- [27], [31] and high bonding pressures, and has been demonstrated with metals such as gold (Au) [22]- [24], aluminum (Al) [25], [26], and copper (Cu) [27], [31]. However, low bonding temperatures during vacuum packaging are desired to avoid thermally induced damages of MEMS devices and CMOS circuits.…”

AlAl thermocompression bonding for wafer-level MEMS sealing

“…Thermocompression bonding using deposited metal films as bonding material is promising for wafer-level encapsulation. Metals such as Au [3,4], Cu [4,5] and Al [4,[6][7][8][9] have been demonstrated as bonding layer between two silicon wafers. Bonding with an intermediate metallic layer is an attractive choice for MEMS devices.…”

“…Successful Al thermocompression bonding has been reported, but only limited details of bonding parameters for wafers having patterned bonding area have been presented [4,[6][7][8][9]. Yun et al bonded wafers by applying a range of bond forces for Al films with a range of Cu impurity levels (0% to 4%).…”

Low Temperature Wafer-Level Metal Thermo-Compression Bonding Technology for 3D Integration

“…Hermetic packaging by Au diffusion bonding at 400°C demonstrated by Xu et al (Xu et al, 2010) achieve a helium leak rate on order of 10 -9 atm.cm 3 /sec based on the MIL-STD-883E method 1014.9 specification. A research of Al diffusion bonding at 450°C by Yun et al (Yun et al, 2008) presents a excellent result of helium leak rate of the order of 10 -12 atm.cm 3 /sec based on the MIL-STD-750E method 1071.8 specification.…”