McGill Nanotools Microfabrication Processes

Matthieu NanniniManager

URL :: miam2.physics.mcgill.ca

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Outline

Microfabrication• Add material• Remove material• Pattern material• To the outside world• Process flow example

Idea to device Conclusion

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Add material: Thermal processes

Atmospheric Chemical Vapour Deposition

Reaction between gases ans substrate at high temperature (900-1100°C)

Precise control of temperature High purity material Si + O2 SiO2 (dry SiO2) Si + H2O SiO2 (wet SiO2)

Available @ McGill: Oxide thermal growth up to 1.5µm

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Add material CVD (Chemical Vapor Deposition)

Low Pressure Chemical Vapour Deposition

Reaction between two gases at high temperature (500-800°C)

Precise control of temperature High purity material 3 SiH2Cl2 + 4 NH3 → Si3N4 + 6 HCl +

6 H2 (silicon nitride) SiH4 → Si + 2H2 (polysilicon)

Available @ McGill: Silicon Nitride LPCVD Amorphous and

polycristalline silicon LPCVD

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Add material: Plasma Enhanced CVD (PECVD)

Plasma Enhanced Chemical Vapour Deposition

Reaction between two gases @ 300-400°C and enhanced by plasma

Allow oxide, nitride or oxynitride to be deposited on metals for insulation or passivation/

High deposition rate: ~1000 A/min Available @ McGill: Silicon Oxide Silicon Nitride Silicon Oxynitride (under

dev.)

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Add material: PVD (Physical Vapor Deposition)

Evaporation• Heat the target material

until it melts and evaporates onto the sample

• Directional coating (shadow effect)

• Low to high etch rates• Stack of material• Materials available: Au,

Ti, Cr, Pd, Al, Ni, Pt …

sample

Add material and pattern at once: lift-off

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samplesample

sample

samplesample

Metal evaporation

Resist

coat

ing

UV pat

tern

ing

develo

pmen

t

Resist dissolution

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Add material: PVD (Physical Vapor Deposition)

Sputtering• Bombard the target with plasma

discharge that extracts atoms from the target onto the sample

• Conformal coating• Conductive and non conductive

material• Reactive sputtering with

additional gas• Stack of material• Co-sputtering alloys• Materials available: Au, Ti, Cr, Al,

AlN, TiN, TiO2, ITO, Cu, Pd, W, Si, SiC…

sample

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Outline

Microfabrication• Add material• Remove material• Pattern material• To the outside world• Process flow example

Idea to device Conclusion

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Remove material: Wet Etch

Wet Etch• Chemical solution• Usually Isotropic (can be

anisotropic in crystals)• Very selective: resist etch

rate vs. material etch rate• High etch rate• Difficult to control precisely• Resolution limitation• Batch processing

Etching

Masking material

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Remove material: Dry Etch

Dry Etch• Gas phase• Sputter + chemical etch• Anisotropic• Less selective• High resolution• Excellent control• Single wafer processing

Gas available @ McGill: Oxides/Nitrides: CF4, CHF3,

O2, Ar Silicon: HBr, Cl2, Ar Metals: HBr, Cl2, Ar, N2, NF3

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Remove silicon: Deep Reactive Ion Etching

DRIE• We need 2 gases, one for etching

and another one to deposit a protective polymer.

• We need to alternate etching and deposition then we pulse the gas injection

• We need energetic ions to remove the polymer on the feature bottom to allow Si etching during SF6 cycle.

available @ McGill: Tegal SDE 110

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Outline

Microfabrication• Add material• Remove material• Pattern material• To the outside world• Process flow example

Idea to device Conclusion

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Pattern material: Photolithography

UV exposition through mask Resolution (~800nm):

• Wavelength (432nm)• mask-substrate distance• resist thickness

To consider• Large exposed area (150mm)• Parallel• Fast• Limited resolution

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Pattern material: Mask design

Designing your mask• Knowing what kind of shapes

you need• How many mask level ?

Alignment needed ?

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Pattern material: Electrolithography

Electron beam direct exposition Principle:

• electron sensitive polymer• Direct beam writing

Resolution: 30nm• E-beam quality (focus,

stigmatism, alignment…)• Stability of stage• Thickness of polymer

To consider• Limited writing areas• Serial writing• slow

E-beam

expose

develop

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Outline

Microfabrication• Add material• Remove material• Pattern material• To the outside world• Process flow example

Idea to device Conclusion

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To the outside world: Dicing

Dicing: • Precision diamond saw to cut out wafer in small dies• Blade thicknesses from 100 to 250µm• Accurate alignment (~ 50µm)

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To the outside world: wire bonding

WireBonder• Connect microelectrodes to the outside world

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Process flow example

cleaning

SiN deposition

Resist patterning

SiN Dry etch

Backside resist patterningwith alignment

SiN backside etch

Top side protection

Backside bulk etch

Remove protection

Beware of Powerpoint engineering !!