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Woodpile Structure Fabrication Chris McGuinness July 8, 2009 Workshop on Novel Concepts for Linear Accelerators and Colliders Working Group 2: Dielectric Laser Accelerators
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Outline Motivation Fabrication Process Fabrication Parameters Layer Adhesion Future Plans
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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
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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
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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
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Four Layer Test Structure
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Fabrication Deviations TargetMeasured Rod Width500nm498nm ± 74nm Tapper Angle0o0o 10.4 o ± 0.6 o Layer Thickness632nm611nm ± 73nm Alignment Offset<80nm138nm Parameter Summary
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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
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Rod Width Measurement Resolution ~25nm
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Layer Thickness Uniformity = 1-2% Controllability = 7% Deposition – LPCVD TEOS
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Layer Adhesion
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Stress
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Annealed Wafer HF Vapor Etch Not Annealed, Vapor HF Etched Not Annealed, Buffered HF Etch Annealed, Buffered HF Etch Annealed, Vapor HF Etch
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Measure Adhesion Strength......
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Future Direction Complete 15 layer structure Optical measurements –Spectroscopy –Coupling –Mode excitation Beam measurements –Wakefield modes Simulations –Consider fabrication variations –Couplers
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THE END
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FTIR Spectroscopy Measurements
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Finite Thickness Simulation Reflection/Transmission (averaged over S&P polarizations, and polar angle θ, φ=0)
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Simulation Reflection/Transmission (averaged over S&P polarizations, and polar angle θ, φ=0)
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Simulation vs. Measurement Bandgap from MPB
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