Outline. Introduction to the LIGA Microfabrication Process. What is LIGA? The LIGA Process. Dr. Bruce K. Gale Fundamentals of Microfabrication

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1 Outline Introduction to the LIGA Microfabrication Process Dr. Bruce K. Gale Fundamentals of Microfabrication What is LIGA? The LIGA Process Lithography Techniques Electroforming Mold Fabrication Analyzing Processing Problems What is LIGA? The LIGA Process LI thographie G alvanoformung A bformung Lithography Electroforming Moulding Lithography For LIGA In general terms lithography is an image transfer process using. Visible and UV Light Electron Beam Ion Beam Laser Machining X-ray The key consideration is high aspect ratio structures are required

2 High Aspect Ratio Patterning Specialized Optical Lithography Processes X-ray Lithography Shadow Printing Using X-rays SU-8 Resist X-ray mask Resist Height: ~360µm Width: ~ 14 µm Height: ~250µm Width: ~ 14 µm Development Critical Parameters in DXRL Exposures Key Features of DXRL Microstructures critical dose: maximum dose underneath absorber to avoid development top dose: maximum dose allowed at top of resist before bubble formation occurs Arbitrary Shape Structure Height up to Several Millimeters Minimum Feature Sizes in the Order of Micrometers Sub-micrometer Topographical Details Vertical Sidewall Profile Smooth Sidewalls bottom dose: minimum dose needed at resist-substrate interface to completely dissolve the resist

3 Deep X-ray Lithography at CAMD X-Ray Two Beam Transport Lines and Scanners for Deep X-ray Lithography Absorber Pattern Pattern Carrier Handling Ring G Exposure Absorbed Dose Peak Dose X-rays W ω Development Level Developed Resist Plating Base Materials: NIST Standard MEMS X-Ray D A =100 mm, D w =100 mm, T=7 mm, L=3 mm, patterned area up to D I =80 mm Handling ring Pyrex, glass, metal Carrier Si(B), SiC, SiN, Si, Be, Ti, C thickness from ~2-5µm up to 200µm Absorber Au, W(Si,N), Ta(Si,N) thickness from ~0.5-1µm up to 50 µm X-ray Membranes for DXRL X-ray Membranes for DXRL Silicon Based (Si, SiC, Si 3 N 4 ) => Acceptable X-Ray Transmission, Mechanically Stiff, Reasonable Optical Transparency(SiC, Si 3 N 4 ), Widely Used Material Titanium Thin Membrane of 1-3 Micrometers Thickness, Reduced Thermal Conduction Characteristics => Acceptable X-Ray Transmission and Stiffness Beryllium => Excellent X-Ray Transmission, Mechanically Stable, Good Thermal Conduction for Cooling Potentially Toxic, not Optically Transparent, High Cost Diamond => Reasonable X-Ray Transmission, Mechanically Stable, Good Thermal Conduction, Optically Transparent Free Standing Membrane in Required Size Range Difficult to Fabricate, High Cost Thin Membrane of 2-3 Micrometers Thickness, Poor Thermal Conduction, no Optical Transparency Rigid Graphite => Reasonable X-Ray Transmission, Rigid, Mechanically Stable, Good Thermal Conduction, Off-the-Shelf Bulk Porosity, Surface Roughness, not Optically Transparent

4 X-ray Fabrication X-ray Fabrication Optical Lithography Intermediate Technique Pattern an optical mask Copy pattern onto an X-ray mask SU-8 Resist Graphite Au electroplating Electroformed Gold Design a pattern Transfer the pattern into a thin resist using an Optical Pattern Generator Finished X-ray X-ray Process Development Exposed Pattern Analysis Graphite as the Membrane Electrodeposited Gold Absorber Sidewall Roughness

5 Secondary Effects in DXRL 3-D X-Ray Lithography Synchrotron Radiation Fuorescence Membrane Absorber Single Exposure with Rotation Double Exposure with Rotation Thermally Induced Motion Resist e - Photoelectrons e Āuger Electrons Resist Thermally Induced Motion Fuorescence Developed Resist Structure Fresnel Diffraction Transition Region Electroformed Metallic Structure Electroforming and Molding Electroplating in High Aspect Ratio Structures - Uniformity Electroplating of metal structures and mold inserts Replication by molding (hot embossing, injection molding) Optimized Plating Conditions Results in more Uniform Deposition of Structures with Different Dimensions.

6 Mold Fabrication Nickel Electroplating Application of Aligned Molding LIGA Acceleration Sensor PMMA structure Ni - structures 120 µm high Detail Redundant Sensor System