1. SCUBA-2 Detector Technology Development
at the University of Edinburgh

2. Current Status
Low stress silicon nitride process conditions have been characterised
PECVD and deep etch ICP equipment delivery expected 10th April 2001
Investigation of possible sources of indium? bump bonding continuing
Technology options still to be agreed

3. Nitride Process

4. Process sequence (1) Grow oxide on 3” silicon wafer
Deposit Metal A layer on back surface (400 /)
Deposit 1µm PECVD SiO2 onto metal (CMP surface finish?)
Etch 10 µm wide trench around perimeter of pixel
Thin second wafer & polish both sides.
33 µm for 450 µm or 62 µm for 850 µm wavelength

5. Process sequence (2) Bond thin wafer to metallised side of thick wafer
Deposit low stress silicon nitride on back face of thin wafer
8) Deposit TES layers on silicon nitride

6. Process sequence (3) Pattern TES structure & form heater
Pattern nitride layer, if required
Deposit leads & aluminium bond pads
Deep etch top wafer to define pixel area
Etch trench in thin wafer through nitride layer

7. Process sequence (4) Fabricate SQUID circuitry on bottom wafer
Form bump pads & indium bumps on front of squid wafer
16) Self align bump bond SQUID wafer to sensor wafer

8. Spacer Option 1 Detector wafer TES 140 / 240 m Spacer wafer
Plated vias
SQUID wafer

9. Spacer Option 2 TES Detector wafer Plated vias 140 / 240 m
SQUID wafer
TES
Plated vias
140 / 240 m

10. Spacer Option 3 Detector wafer TES 140 / 240 m Spacer wafer
Plated vias
SQUID wafer

11. Spacer Options Issues High apect ratio through wafer etch required
Through hole plating required
Weakening of waffle grid (option 2)
Gap set by solder
Bump bonding with membrane formed
Thin spacer wafers required (cost + processing)
Large solder bumps (option 3)

12. Bonded Technology Option Issues
Bump height not critical
Bump bonding before membrane formation possible
Thin wafers or grinding technology required
Need conductor 400 / ȱ that can withstand high wafer bonding temperature, adheres well to oxide and is not superconducting
Thin polished wafers will be expensive
Wafer bonding technology toolkit required
Wafer bonding technology needs to be developed

13. Bonded Technology Toolkit
Essential tools
Wafer bonding tool
Bond inspection kit (IR)
Particulate inspection tool
Class 1 area
Optional tools
Wafer grinding tool (thinned wafer $200)
- cycle time/ cost trade-off
Thickness measurement (?)