1. Berkeley Sensor & Actuator Center Latest Result Multiple Wafer Bonding Process Lixia Zhou, Matt Last Joseph M. Kahn Kristofer S. J. Pister October 16, 2002

2. Berkeley Sensor & Actuator Center Spontaneous hydrophilic Si bonding Infrared picture of spontaneous wafer bonding. a) Start of bonding by applying a slight pressure, b) Extension after 2 sec, c) Complete bonding after about 5 sec. Maximum bonding wave velocity observed: 2 cm/s.

3. Berkeley Sensor & Actuator Center Why bonding? Scanning Mirror Veljko Milanovic, Matt Last, Kris Pister

4. Berkeley Sensor & Actuator Center Patterned SOI alignment bonding to realize multi-layer devices

5. Berkeley Sensor & Actuator Center Process flow I: SCSWet Oxide PR

6. Berkeley Sensor & Actuator Center Process flow II: SCSWet Oxide PR

7. Berkeley Sensor & Actuator Center Process flow III: SCSWet Oxide PR

8. Berkeley Sensor & Actuator Center Problems coming across bonding Ksaligner Si/Si bonding alignment accuracy is within +/- 30um. Design rule has to take care of this. Bow/warpage of SOI wafer is preventing a secure bonding. Retaining an oxide layer on the back of handle wafer helps to reduce the bow. Thermal stress from oxide membrane causes cracks and even breaks off part of the membrane during and after STS handle wafer etch. Having a thinner oxide membrane helps to reduce the stress.

9. Berkeley Sensor & Actuator Center Stress from thermal oxide membrane

10. Berkeley Sensor & Actuator Center Stress from thermal oxide membrane

11. Berkeley Sensor & Actuator Center Working 1D scanning mirror realized by bonding

12. Berkeley Sensor & Actuator Center 1D scanning mirror: DC actuation Comb drive pull_in Compared with Veljko and Matt’s timed etch mirror: 20 degrees at 90V or 6 degrees at 56V. * *

13. Berkeley Sensor & Actuator Center 2D scanning mirror realized by bonding

14. Berkeley Sensor & Actuator Center Testing structures pressure sensor pillar and roof bond strength measurement

15. Berkeley Sensor & Actuator Center Process works great! High yield. Need a more powerful simulation tool. Problems associated with comb drive pull_in and 2D scanning mirror coupling can be solved with better design. New design ideas are welcome. Microrobots? And what’s more?