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

The study of wafer level hermetic bonding using sub-micron gold particles with the mean diameter of 0.3_m was conducted at bonding temperature of 150 – 300 °C with varying bonding pressure in the range of 50 – 100 MPa. 4.5 mm-square, 10 μm – 100 μm-wide seal line patterns of sub-micron Au particles were formed on Si or glass wafers by means of wafer level processing using photolithography and slurry filling technique. Tensile bond strength was measured by stud-pull method using 5 mm x 5 mm chips as > 20 MPa. A preliminary test for hermeticity was performed by immersing the bonded wafer pairs into a low viscosity liquid and it was confirmed that the seal lines with the width as thin as 20 _m showed good sealing property for the liquid. The result demonstrated the feasibility that this low temperature wafer bonding process using sub-micron Au particles could absorb a micron level surface roughness or topography with achieving hermeticity.