1. McGill Nanotools Microfabrication Processes
Matthieu Nannini
Manager
URL :: miam2.physics.mcgill.ca

2. Outline Microfabrication Idea to device Conclusion Add material
Remove material
Pattern material
To the outside world
Process flow example
Idea to device
Conclusion

3. Add material: Thermal processes
Atmospheric Chemical Vapour Deposition
Reaction between gases ans substrate at high temperature ( °C)
Precise control of temperature
High purity material
Si + O2  SiO2 (dry SiO2)
Si + H2O  SiO2 (wet SiO2)
McGill:
Oxide thermal growth up to 1.5µm

4. Add material CVD (Chemical Vapor Deposition)
Low Pressure Chemical Vapour Deposition
Reaction between two gases at high temperature ( °C)
Precise control of temperature
High purity material
3 SiH2Cl2 + 4 NH3 → Si3N4 + 6 HCl + 6 H2 (silicon nitride)
SiH4 → Si + 2H2 (polysilicon)
McGill:
Silicon Nitride LPCVD
Amorphous and polycristalline silicon LPCVD

5. Add material: Plasma Enhanced CVD (PECVD)
Plasma Enhanced Chemical Vapour Deposition
Reaction between two °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
McGill:
Silicon Oxide
Silicon Nitride
Silicon Oxynitride (under dev.)

6. 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

7. Add material and pattern at once: lift-off
Resist coating
sample
sample
UV patterning
sample
Metal evaporation
development
sample
sample
Resist dissolution

8. 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

9. Outline Microfabrication Idea to device Conclusion Add material
Remove material
Pattern material
To the outside world
Process flow example
Idea to device
Conclusion

10. Remove material: 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
Masking material
Etching

11. Remove material: Dry Etch
Gas phase
Sputter + chemical etch
Anisotropic
Less selective
High resolution
Excellent control
Single wafer processing
Gas McGill:
Oxides/Nitrides: CF4, CHF3, O2, Ar
Silicon: HBr, Cl2, Ar
Metals: HBr, Cl2, Ar, N2, NF3

12. 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.
McGill: Tegal SDE 110

13. Outline Microfabrication Idea to device Conclusion Add material
Remove material
Pattern material
To the outside world
Process flow example
Idea to device
Conclusion

14. 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

15. Pattern material: Mask design
Designing your mask
Knowing what kind of shapes you need
How many mask level ? Alignment needed ?

16. Pattern material: Electrolithography
E-beam
expose
develop
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

17. Outline Microfabrication Idea to device Conclusion Add material
Remove material
Pattern material
To the outside world
Process flow example
Idea to device
Conclusion

18. To the outside world: Dicing
Precision diamond saw to cut out wafer in small dies
Blade thicknesses from 100 to 250µm
Accurate alignment (~ 50µm)

19. To the outside world: wire bonding
WireBonder
Connect microelectrodes to the outside world

20. Process flow example Beware of Powerpoint engineering !! cleaning
SiN backside etch
SiN deposition
Top side protection
Resist patterning
Backside bulk etch
SiN Dry etch
Remove protection
Backside resist patterning
with alignment
Beware of Powerpoint engineering !!