High speed, low driving voltage vertical cavity germanium-silicon modulators for optical

Appendix B 
This appendix gives the full fabrication process of high-speed modulator device. 
Optical Two-level Mesa Lithography (Mask Mesa) 
20 min singe at 120°C
Wafer prime for 40sec 
Spin 3612 photoresist at 5000rpm for 40sec
2 min bake @ 90°C 
Expose 1.2 sec @ 30mW/cm
2 
using Karl Suss Aligner Develop 60sec in LDD26W 
(1.2 μm thick),
CF
4
Plasma etch, 100sccm O
2
, 190mT, 500W, for 120seconds
PRX127 clean at 25°C for 20 min 
LPCVD Deposition 
Tylan BPSG use recipe LTO400 at 400°C. The pressure is roughly 350mtorr. Silane 
and oxygen are used in this process without phosphine doping. Deposition time is 30 
min 
Back Etch 
20 min singe at 120°C
Wafer prime for 40s 
Spin 3612 photoresist at 5000rpm for 40sec
2 min bake @ 90°C 
Dip in 20:1 buffered oxide etchant (BOE) for 6 min.Monitor the residual oxide 
thickness every 2 minutes during the wet etch. Use Nanospec to measure the thickness 
Oxide window etching (Oxide Window Mask) 

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20 min singe at 120°C
Wafer prime for 40sec 
Spin 3612 photoresist at 5000rpm for 40sec
2 min bake @ 90°C 
Expose 1.2 sec @ 30mW/cm
2
using Karl Suss Aligner
Develop 60sec in LDD26W (1.2 μm thick),
Dip in 20:1 buffered oxide etchant (BOE) for 6 min.Monitor the residual oxide 
thickness every 2 minutes during the wet etch. Use Nanospec to measure the thickness 
PRX127 clean at 25°C for 20 min 
Contact deposition (Contact Mask) 
20 min singe at 120°C
Wafer prime for 40sec 
Spin 3612 photoresist at 3000rpm for 40sec
2 min bake @ 90°C 
Expose 1.7 sec @ 30mW/cm
2
using Karl Suss Aligner
Develop 60sec in LDD26W (1.2 μm thick), 
Dip in 50:1 HF for 30 sec 
Use e-beam evaporator to deposit 30nm of titanium (Ti) and 1

m of Aluminum (Al) 
Rapid thermal anneal (RTA) at 375º
C for 30 seconds. 

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