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 mum 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 ~ 450degC with various bond forces up to 80 kN. The leak detection on the capped device showed the superb hermeticity of ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> atm/sec He leak rate with an Al seal width as narrow as 3 mum. And the electrical contact resistance of the Al to Al bonded interface measured less than 1 Omega.