Ultrasonic and thermo-compression gold-to-gold bonding of narrow frames for hermetic cavity sealing and electrical interconnect

Cavity sealing based on ultrasonic or thermo-compression gold-to-gold bonding of rather narrow, 5 to 20 μm wide frames on die-to-wafer level is investigated. The seal quality is tested with an aggressive alkaline etch solution (33% KOH, at 90°C) using an aluminum test layer, which in the case of poor sealing, is readily attacked. Sealing of large cavities (~3×9 mm²) with sealing ring widths of 10 and 20 μm for the ultrasonic as well as sealing of small cavities (70×70 μm²) with a 5 μm wide sealing ring for the thermo-compression bonding is demonstrated. The thermocompression provides better bonding of the narrower features than the ultrasonic technique.