1. MEMS Two-Phase Vapor Escape Heat Exchanger
Milnes David
Tarun Khurana
Christopher Anderson

2. Process Flow Diffusion Clean Oxide Growth Al. Sputter
Backside Pattern (heaters & sensors)
Al Etch
Ashing
PRX 1000 Clean
Backside LTO deposition
Backside protect
Front-side Oxide Etch (HF)
Front-side pattern (channels)
Front-side channel etch (STSDRIE)
Backside pattern (bond pads)
Pad etch

3. Process Layout Backside pattern (through etch) Through etch (STS DRIE)
Final released device
Adhesive coat on transfer substrate
Contact printing of adhesive
Membrane attachment via UV curing
Attachment of patterned double sticky tape (vapor channel)
Top cover integration

4. Images of the Heaters and Sensor
open bond pads

5. Typical Defects Shorts (bridging) Voids
Scratches – due to handling errors, motivates thicker LTO deposition (5000 A)

6. Resistance Measurements
4.4
250 ?
401
150
385
506
400 43
389 44 ? 42
383 43
381
410
397
393
423
380
367
5.0
Ground lines = 4.7 ± 0.4 
Sensors = 392 ± 15 
Heaters = 43 ± 0.8 
In all cases resistance is almost twice as high as predicted.

7. LTO300 Deposition Average dep rate: alternate arrangement = 58 A/min
Consecutive arrangement = 40 A/min
Average etch rate pad-etch rate:
LTO oxide = 3540 A/min
Thermal oxide = A/min

8. STS issues STS down for a month, expected to be up by 1st week of Aug.
Alternatives Pursued:
Getting trained on STS2 (through-etch still not possible)
Outside DRIE and machining service vendors
American precision dicing (can do through etch features)
Laserod laser machining (~ $200 per wafer)
ISSYS
Honeywell MEMS foundry
IMT
Investigated UC-Berkeley and UCSB fab
Training and qualification time is an issue (about a week in each case)
Investigating wet etch options (KOH or TMAH)
Requires oxide or nitride as mask
Significant undercutting can result in much larger features
Changing process flow to perform pad etch first to save time.
Created back-up device in Copper.

9. Design of Copper Device

10. Thanks!
Questions?