Low-Temperature Wafer Bonding for MEMS Hermetic Packaging Using Sub-micron Au Particles

Abstract

A study of wafer-level hermetic bonding using sub-micron gold particles with a mean diameter of 0.3 μm was conducted at bonding temperatures of 150–200°C with varying bonding pressures in the range of 50–100 MPa. 4.5 mm-square, 10 μm–100 μm-wide sealing line patterns of sub-micron Au particles were formed on glass wafers by means of wafer-level processing using photolithography and a slurry-filling technique. The tensile bond strength was measured with a stud-pull method using 5 mm × 5 mm chips and exhibited as > 20 MPa. A preliminary hermeticity test was performed by immersing the bonded wafer pairs into a low-viscosity liquid and it was confirmed that the sealing lines with widths as thin as 20 μm showed a good sealing property against the liquid. The result demonstrated the feasibility of this low-temperature wafer bonding process using sub-micron Au particles, which could achieve hermetic sealing with absorbing a micron-level surface roughness and/or topography.