Low-temperature, surface-compliant wafer bonding using sub-micron gold particles for wafer-level MEMS packaging

Low-temperature wafer bonding using sub-micron gold particles was investigated. For more flexible bonding pattern deposition, wafer-level pattern transfer method has been developed to enable patterning on fragile structures such as MEMS devices. Sub-micron Au particle patterns with a width of 20 μm-60 μm and a height around 20 μm were formed on 100mm-diameter glass wafers by means of wafer-level processing using photolithography and a slurry-filling technique, and then successfully transferred onto Si wafers in ambient atmosphere at a temperature of 150°C and an applied pressure of 20 MPa-30 MPa. Finally, wafer bonding was performed at 200°C, 100 MPa and confirmed a sufficient tensile strength of 45.8 MPa. Compression deformation measurement was performed and the performance on a-few-μm surface roughness absorption was demonstrated. A feasibility of further reduction of bonding temperature has been suggested by showing sintering behavior of smaller-sized Au particles at 150°C.