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Microfabrication Technologies

Luiz Otávio Saraiva Ferreira

LNLS

lotavio@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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• Stencil

UV LIGHT

GLASS OR QUARTZ

PHOTORESIST

SUBSTRATE

LIGHT ABSORBER(800A Cr)

1:1 IMAGE

• Light Field

• Dark Field

Lithographic Masks

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PHOTORESIST

Si SUBSTRATESiO2

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.

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Transfer of Patterns

Si

SiO2

Photoresist

RadiationGlass

Metal

Unexposed Photoresist

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6

4

2

3

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Karl Suss MA4

Mask Aligner

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Ultra Violet or X-Ray Source

Mask

Before Exposure Exposure After Development

3D LithographyTechniques

Thornell & Johansson, J. Micromech. Microeng. (1998) 251-262

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Bulk Silicon Micromachining

Wet or Dry Etch

A B

ISOTROPIC

Isotropic AnisotropicSelective

ANISOTROPIC

Sci. Am. April 1983 pp. 39

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Back and Front Side Back and Front Side Bulk MicromachiningBulk Micromachining

Suspensedevices

MembraneBack Side Etch

Front Side Etch

Cantilever

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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 MicromachiningEtch

Before etch

After etch

CantileverBridge

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Example of Surface Micromachining

Sandia

Germany - 80’s

Resist

Base Plate

IRRADIATION

Base Plate

Resist structure

DEVELOPMENT

ELECTROFORMING

Metal

Resist Structure

Base Plate

MOLD FABRICATION

Mold Insert

Mold Cavity

Synchrotron Radiation

Mask membraneAbsorber structure

MOLD FILLING

Mold Insert

Mold MaterialGate Plate

Injection Hole

DEMOLDING

Plastic Microstructure

PLASTIC MOLDING

Mold Insert

Mold Material

Plastic Structure(Lost Mold)DEMOLDING

SLURRY CASTING

Ceramic Slurry

Plastic Structure(Lost Mold)

FIRING

Ceramic Micro-structure

ELECTROFORMING

Metal

Gate Plate

Injection Hole

Metallic Micro-structure

FINISHING

Plastic Structure

LIGA Technology

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X-Ray

Be Filter (125um)

Al Filter

100um thick SU-8 film

Si substrate

Au absorber (1.8um) 20um SU-8

Kapton mask Plating Base (0.2um Au)

5 - 15 keV spectrum after filtering

Deep X-ray Lithography

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•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.

Resists for deep X-ray Lithography

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20µm thick UV-LIGA process.

Deep UV lithography on

SU-8.

Au platting.

Frame

25µm thick Kapton Membrane

Plating Base

2µm Au 20µm SU-8

Kapton Mask

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UV

Cheap

Non-vertical sidewalls - border diffraction effect.

RX

Expensive

Vertical sidewalls - negligible border diffraction.

Deep UV lithography Deep X-ray lithography

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