1. Eutectic Wafer Bonding Susoma, Jannatul

2. Eutectic WB • Low bonding temperature • Fewer restrictions with Substrate roughness and Flatness • Better out-gassing • Better Hermeticity Bonding of Si wafer to glass or silicon wafer coated with Au or Al layer Advantage: • Intermediate metal (Sn, Ag, Al, Au) layer • Semiconductor-metal Alloys formation • Vacuum Condition • Liquid face

3. Eutectic WB • Temperature Uniformity • Very Good temperature control • Both side or one side substrate heating • very low contact force

4. Eutectic WB Vs Thermo-compression WB

5. Si-Au Eutectic WB Phase Diagram • Au-Si Eutectic Bonding Temperature 363 oC • Si melting point 1412 oC • Au melting point 1063 oC

6. Si-Au Eutectic WB Temperature Effect • Higher Temperature (> Eutectic Temperature): • Thicker layer of Au-Si Alloy • Strong Bonding • Too higher Temperature: • serious diffusion • Less reliable • Degrade the function of Silicon device

7. Bond Strength Vs Bond Temperature for Si-Au Eutectic Bonding • Higher Bonding Strength: • Better quality • reliability • At 400 oC, maximum bond strength of 18 MPa • Increases in temperature beyond 400 oC to 475 oC, bond strength reduces to 15.8b MPa

8. Si-Au Eutectic WB Using Localized Heating Method • High bonding strength • Good stability • Faster process • Relatively low processing temperature ( 363 oC) • Localized Heating

9. Checking for wafer-to-wafer bonding integrity • Three dominant methods for imaging a bonded pair of silicon wafer • Infrared transmission • Ultrasonic • X-ray topography

10. Visualization of the bonded wafer pair X-ray topography Ultrasonic IR transmission

11. Bonding Strength Measurement

12. Thank you