1. 1 Kimberly Manser 5.14.2008 Process Development for Double-Sided Fabrication of a Photodiode Process Development of a Double-Sided Photodiode (for application on SNAP – SuperNova Acceleration Probe) Rochester Institute of Technology Department of Microelectronic Engineering In Conjunction with Rochester Imaging Detector Lab (RIDL) In Association with NASA and the US Department of Energy Kimberly Manser Advisor – Dr. Lynn Fuller

2. 2 Background Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode SNAP (SuperNova Acceleration Probe) is a space observatory that will measure the expansion of the universe by tracking supernova as markers. This information will also help scientists understand the nature of dark matter and its role in the acceleration of the expansion of the universe. SNAP is a part of the Joint Dark Energy Mission (JDEM), part of the Beyond Einstein program to understand the universe. The photodetector described is a candidate for the focal plane array on the observatory.

3. 3 Introduction Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode Cross-Section and Topographic Requirements: Junction Depths Less than 1um Minimal Shadowing 15μm Pixel Pitch Frontside (Bonds to Multiplexer) Backside (Collects Radiation) Bump Bonding Sites

4. 4 Device Goals Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode Dark Current: Dark Current: 0.1 pA / cm 2 at 200K at a 50V bias 15 nA / cm 2 at 300K (testing temperature) at a 50V bias N+ Implant (Front Surface Field): Junction Depth < 0.75 μ m Surface Concentration 1x10 18 cm -3 P+ Implant (Back Surface Field): Junction Depth < 0.5 μ m Surface Concentration 1x10 19 cm -3

5. 5 Challenges and Solutions Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode Special ProcedureFront to Back Alignment Wet Etches Initially ChosenSelectivity / Over-Etching LTO / RTALimited Thermal Budget Protective Layers / Proximity Bakes“Backside” Contamination

6. 6 Silvaco Implant Profile Simulations Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode μmμm Atoms per cm 3 Phosphorus ImplantBoron Implant 1x10 18 cm -3 2x10 19 cm -3

7. 7 Process Flow Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode Backside Alignment Marks in Silicon Backside Implant (N ++ P 31 ) Backside Film Stack and Protective Layer Frontside Alignment Marks in Silicon Frontside Implant (P ++ BF 2 ) Frontside Film Stack Backside Metal Frontside Metal Passivation Backside Alignment Marks in Silicon Backside Implant (N ++ P 31 ) Backside Film Stack and Protective Layer Frontside Alignment Marks in Silicon Frontside Implant (P ++ BF 2 ) Frontside Film Stack Backside Metal Frontside Metal Passivation

8. 8 Testing Run Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode  No Photolithography Steps Blanket Implants – easier to measure bulk sheet resistance (by 4-pt. Probe) and junction depth (by Groove and Stain)  No Metalization Steps P ++ Si N ++ Si 5000 Ω-cm N-Si

9. 9 Testing Run Results Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode  Updated deposition rate for LTO  Increased Phosphorus Implant Dose  Decrease in Boron Implant Screening Oxide Thickness

10. 10 Device Fabrication Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode  Three Device Wafers  Two Monitor Wafers Implant Metal Thickness  55 Steps Total  95 Tool Hours

11. 11 Device Fabrication Results Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode

12. 12 Device Fabrication Results (cont’d) Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode Sample Ideality Factor (n) D11.36 D21.26 D31.31 N-Implant Sheet Resistance994 Ω / □ Junction Depth0.76 μm Surface Concentration3x10 18 cm -3 P-Implant Sheet Resistance1085 Ω / □ Junction Depth0.44 μm Surface Concentration2x10 19 cm -3 Testing Structure 1965 μm 2010 μm

13. 13 Device Fabrication Results (cont’d) Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode Current ( A / cm 2 ) I-V Characteristic Curve

14. 14 Device Fabrication Results (cont’d) Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode Frontside Backside

15. 15 Conclusions and Future Work Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode Contact Etch Issues Dry Etch Tests and Process Development Dark Current Issues Optimization of Anneals Characterization of Perimeter Parasitics

16. 16 Acknowledgements Kimberly Manser Process Development for Double-Sided Fabrication of a Photodiode Dr. Lynn Fuller Dr. Karl Hirschman Dr. Sean Rommel Tom Grimsley Dr. Jingjing Zhang Dr. Don Figer Bruce Tolleson Sean O’Brien David Yackoff