Page 94 - An Introduction to Microelectromechanical Systems Engineering

Combining the Tools—Examples of Commercial Processes 73

Figure 3.31 Scanning electron microscope image of a 200-µm-deep thermal actuator fabricated
using silicon fusion bonding and DRIE. (Courtesy of: GE NovaSensor of Fremont, California.)

Buried oxide

Silicon Silicon
Silicon Silicon
Oxide Oxide
1. DRIE top side of SOI wafer 2. Double-sided alignment.
stopping on oxide. DRIE back side of SOI wafer
stopping on oxide.
Freestanding structure
Structure overlaps
bottom silicon
Silicon
Oxide Silicon Stucture is over

free space
3. Etch buried oxide in HF
Figure 3.32 Example process for DRIE of SOI wafers. The final structure may be over free space
or can overlap the bottom wafer (or both, as in this example).

Freestanding
actuator

Top
wafer

Actuator overlaps
bottom wafer
Package
Bottom wafer
Figure 3.33 Scanning electron microscope image of a variable optical attenuator made by DRIE
of an SOI wafer. (Courtesy of: DiCon Fiberoptics, Inc., of Richmond, California.)