Microfabrication Technologies

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Microfabrication Technologies

• Luiz Otávio Saraiva Ferreira
• LNLS
• lotavio_at_lnls.br

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OUTLINE

• Lithography
• Transfer of Patterns
• Bulk Silicon Micromachinning
• Surface Micromachinning
• LIGA technique

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Litography - Evolution

• France, 1822
• Graphic arts.
• Printed circuit board- 1940-1945.
• 0.1mm wide lines.
• (It may be used for microfluidics).
• Integrated circuit - 1961.
• 5um wide lines.
• Wide evolution on electronics industry.
• Microsystems require progress on 3D lithography.

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Lithographic Masks

• Stencil

UV LIGHT
11 IMAGE
GLASS OR QUARTZ
LIGHT ABSORBER (800A Cr)
PHOTORESIST
SUBSTRATE

• Light Field
• Dark Field

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Photoresist processing

• Spinning
• Most used substrate Si/SiO2
• Si Oxidation
• Wet or dry.
• Between 900 and 1150oC.
• SiO2 masks the substrate in the following
  processing steps.

PHOTORESIST
SiO2
Si SUBSTRATE
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Transfer of Patterns
Photoresist
SiO2
Si
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2
Radiation
Unexposed Photoresist
Glass
Metal
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3
6
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Mask Aligner
Karl Suss MA4
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3D LithographyTechniques
Ultra Violet or X-Ray Source
Mask
Before Exposure
Exposure
After Development
Thornell Johansson, J. Micromech. Microeng.
(1998) 251-262
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Bulk Silicon Micromachining
A
B
Isotropic
Selective
Anisotropic
Sci. Am. April 1983 pp. 39
Wet or Dry Etch
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Back and Front Side Bulk Micromachining
Suspensedevices
Membrane
Back Side Etch
Cantilever
Front Side Etch
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Problems of Bulk Micromachining
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Corner Compensation
No compensation
Beginning etch
Mid etch
End of etch
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Surface Micromachining
Etch
Before etch
Cantilever
Bridge
After etch
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Example of Surface Micromachining
Sandia
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LIGA Technology
Germany - 80s
Synchrotron Radiation
Mold Insert
Mold Material
Mask membrane
Absorber structure
PLASTIC MOLDING
Resist
Plastic Structure (Lost Mold)
Base Plate
DEMOLDING
IRRADIATION
Ceramic Slurry
Resist structure
Base Plate
DEVELOPMENT
Plastic Structure (Lost Mold)
Metal
SLURRY CASTING
Resist Structure
Ceramic Micro-structure
Base Plate
ELECTROFORMING
Mold Insert
FIRING
Metal
Mold Cavity
Plastic Structure
MOLD FABRICATION
Mold Insert
Gate Plate
ELECTROFORMING
Mold Material
Injection Hole
Gate Plate
Metallic Micro-structure
MOLD FILLING
Injection Hole
Plastic Microstructure
FINISHING
DEMOLDING
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Deep X-ray Lithography
X-Ray
Be Filter (125um)
Al Filter
Kapton mask Plating Base (0.2um Au)
Au absorber (1.8um)
20um SU-8
100um thick SU-8 film
Si substrate
5 - 15 keV spectrum after filtering
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Resists for deep X-ray Lithography

• PMMA (polymethylmetacrylate)
• the most used.
• High resolution.
• Low sensitivity (2.5 kJ/cm3 minimum dose).
• Long exposure times.
• Up to 100µm thick ? 1-3 keV energy.
• From 100µm to 500µm thick ? 3 - 7 keV energy.
• SU-8 (epoxy based)
• a promising material
• Good resolution.
• High sensitivity.
• Short exposure times.
• Difficult processing.

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Kapton Mask
20µm thick UV-LIGA process. Deep UV lithography
on SU-8. Au platting.
2µm Au
20µm SU-8
Plating Base
25µm thick Kapton Membrane
Frame
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Deep UV lithography ? Deep X-ray lithography
UV Cheap Non-vertical sidewalls - border
diffraction effect. RX Expensive Vertical
sidewalls - negligible border diffraction.
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