1. Woodpile Structure Fabrication Chris McGuinness July 8, 2009 Workshop on Novel Concepts for Linear Accelerators and Colliders Working Group 2: Dielectric Laser Accelerators

2. Outline Motivation Fabrication Process Fabrication Parameters Layer Adhesion Future Plans

3. Motivations 0 10 1 SiO 2 E acc =2.76 GV/m @800nm(3.75e5GHZ) Si E acc =337 MV/m @1550nm(1.94e5GHZ) Al 3 O 2 E acc =2.0 GV/m @800nm(3.75e5GHZ) ZnS E acc =1.04 GV/m @5μm(6e4GHZ) Ratio=1.41 Gradient Sources Fabrication

4. 4 3 w a SiO 2 resist Silicon Substrate SiO 2 poly-si Si Substrate Photo resist 1 2 h SiO 2 5 Poly-si Fabrication Process Step 1: SiO 2 Deposition - LPCVD Uniformity = 1-2% Controllability = 7% Step 2: Resist Coat Step 3: Optical Lithography Minimum feature size 450nm Alignment 3σ=60nm Step 4: Plasma etch SiO 2 Step 5: Poly-si Deposition

5. Fabrication Process 6 8 7 SiO 2 poly-si Time Frictional Force 10sec=15nm Step 6: Chemical Mechanical Polish Step 7: Repeat process for remaining layers Final Step: HF Vapor Etch

6. Four Layer Test Structure

7. Fabrication Deviations TargetMeasured Rod Width500nm498nm ± 74nm Tapper Angle0o0o 10.4 o ± 0.6 o Layer Thickness632nm611nm ± 73nm Alignment Offset<80nm138nm Parameter Summary

8. Tapper Angle 3.4 o ~0 o 6.6 o 5.1 o CHF 3 85 sccm O 2 6 sccm CF 4 50 sccm CH 3 F 20 sccm Ar 100 sccm CF 4 50 sccm CH 3 F 25 sccm Ar 120 sccm P5000 -Magnetically Enhanced RIE AMT 8100 - Hexode Plasma Etcher CHF 3 50 sccm O 2 30 sccm

9. Rod Width Measurement Resolution ~25nm

10. Layer Thickness Uniformity = 1-2% Controllability = 7% Deposition – LPCVD TEOS

11. Layer Adhesion

12. Stress

14. Annealed Wafer HF Vapor Etch Not Annealed, Vapor HF Etched Not Annealed, Buffered HF Etch Annealed, Buffered HF Etch Annealed, Vapor HF Etch

15. Measure Adhesion Strength......

16. Future Direction Complete 15 layer structure Optical measurements –Spectroscopy –Coupling –Mode excitation Beam measurements –Wakefield modes Simulations –Consider fabrication variations –Couplers

17. THE END

18. FTIR Spectroscopy Measurements

19. Finite Thickness Simulation Reflection/Transmission (averaged over S&P polarizations, and polar angle θ, φ=0)

20. Simulation Reflection/Transmission (averaged over S&P polarizations, and polar angle θ, φ=0)

21. Simulation vs. Measurement Bandgap from MPB