MEMS Two-Phase Vapor Escape Heat Exchanger

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MEMS Two-Phase Vapor Escape MEMS Two-Phase Vapor Escape Heat Exchanger Heat Exchanger

Milnes David

Tarun Khurana

Christopher Anderson

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Process Flow

1. Diffusion Clean

2. Oxide Growth

3. Al. Sputter

4. Backside Pattern (heaters & sensors)

5. Al Etch

6. Ashing

7. PRX 1000 Clean

8. Backside LTO deposition

9. Backside protect

10. Front-side Oxide Etch (HF)

11. Front-side pattern (channels)

12. Front-side channel etch (STSDRIE)

13. Backside pattern (bond pads)

14. Pad etch

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Process Layout

15. Backside pattern (through etch)

16. Through etch (STS DRIE)

17. Final released device

18. Adhesive coat on transfer substrate

19. Contact printing of adhesive

20. Membrane attachment via UV curing

21. Attachment of patterned double sticky tape (vapor channel)

22. Top cover integration

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Images of the Heaters and Sensor

open bond pads

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Typical Defects

1. Shorts (bridging)

2. Voids

3. Scratches – due to handling errors, motivates thicker LTO deposition (5000 A)

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Resistance Measurements

4.4

5.0

367

? 381383 43424438943

410

400

? 385

393

150

397

401

250

380

506

423

Ground lines = 4.7 ± 0.4

Sensors = 392 ± 15

Heaters = 43 ± 0.8

In all cases resistance is almost twice as high as predicted.

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LTO300 Deposition

0

20

40

60

80

100

120

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Boat Position

Dep

osi

tio

n (

A/m

in)

Dummy

Good

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 = 400-600 A/min

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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.

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Design of Copper Device

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Thanks!

Questions?