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

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

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

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

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.)

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 Resist coating sample sample UV patterning sample Metal evaporation development sample sample Resist dissolution

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

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

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

Remove material: 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

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

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

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

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

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

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

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

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

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 !!