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

Outline Motivation Fabrication Process Fabrication Parameters Layer Adhesion Future Plans

Motivations SiO 2 E acc =2.76 Si E acc =337 Al 3 O 2 E acc =2.0 ZnS E acc =1.04 Ratio=1.41 Gradient Sources Fabrication

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

Fabrication Process 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

Four Layer Test Structure

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

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 Hexode Plasma Etcher CHF 3 50 sccm O 2 30 sccm

Rod Width Measurement Resolution ~25nm

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

Layer Adhesion

Stress

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

Measure Adhesion Strength......

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

THE END

FTIR Spectroscopy Measurements

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

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

Simulation vs. Measurement Bandgap from MPB