Advanced resists for e-beam lithography: processing ... · M. Pojar & A.C.Seabra Advanced resists...
Transcript of Advanced resists for e-beam lithography: processing ... · M. Pojar & A.C.Seabra Advanced resists...
M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/2015 1
Advanced resists for e-beam lithography: processing, exposure
and characterization(Part III)
Dra. Mariana Pojar de MeloProf. Dr. Antonio Carlos SeabraDep. Eng. de Sistemas Eletrônicos
Escola Politécnica da [email protected], [email protected]
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Processing Steps for Lithography
HardBake
DehydrationBake
AdhesionPromoter
ResistSpinning Pre-bake
ExposurePost-exposureBakeDevelopmentPlasma
Flash
Etching
Deposition(Lift-off)
Substrate cleaning
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Lift-off (one monolayer)
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Lift-off (bilayers - PMMA and PMGI)
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Transferring patterns to the sample Etching (wet or dry)
resistmetalsubstrate
Metal and resist deposition
resistmetalsubstrate
Exposure
metalsubstrate
Resist development
Etching
substratemetal
wet Dry
Lift-offresist 2resist 1substrate
Depositions
resist 2resist 1substrate
Direct write
resist1substrate
resist 2Development 1
resist 1substrate
resist2Development 2
metalDeposition
metalLift-off
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Lift-off (bilayers - PMMA and PMGI)
Dependência do tamanho da abertura definida na camada superior no tamanho do undercut. Quanto maior for o tamanho da abertura maior será o tamanho do undercut.
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Lift-off (bilayers - PMMA and PMGI)
Dependência da concentração do solvente do solvente no tamanho do undercut para um sistema ZEP520/LOR. Na figura 4.a o solvente estava concentrado e na Figura 4.c o solvente estava diluído em 40% onde se verifica que a camada inferior não foi removida completamente.
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Lift-off using a Bilayer (ZEP520/PMGI)
For nanolithography, the production of high-resolution objects requires a precise control of theundercut length.
90nm metal deposition
ZEP-520
PMGI
substrate
AFTER LIFT-OFF:
Cr line -90nm
Cr line - 70nm
Deyu et al., A ZEP 520-LOR bilayer Resist Lift-off Process by e-beam lithography for nanometer pattern Transfer, IIIE, 2007.
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CORRECTION ON AN OPTICAL LITHOGRAPHY MASK
TRANSISTORS
IS EASY TO MAKE A SIMPLE LITHOGRAPHY ON AN INSULATOR
SUBSTRATE????
MICRO AND NANO STRUCTUREs FABRICATION ON INSULATOR SUBSTRATES
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CHARGING EFFECT
Electron Beam
resist
Insulator substrates
Initial Condiction
resist
Insulator substrates
Future Condiction
Repulsive electricpotential lines
Negative charge acumullation
CAUSE BEAM DEFLECTION AND
THUS PATTERNING DISTORTIONS
nanolithography.gatech.edu/anti_charging html
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PATTERNING DISTORTIONS DUE TO CHARGING EFFECT
Substrate: 1um thermal oxide
Substrate: MgF2
Substrate: glass
Anothers possible insulators substrates: Quartz, glass;
SiO2, Si3N4 (semiconductor application);
GaN, sapphire (opto-electronics);
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PATTERNING DISTORTIONS DUE TO CHARGING EFFECT
Substrate: optical masksResist: PMMA(140nm)/ PMGI(120nm) with adhesion promoter Omnicoat
Spot=1,0; FC current= 0,0147nA;DT=78,019us;800x magnification30kV
How to minimize this effect?
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COMERCIAL SOLUTION Espacer Conducting polymer; Produced by Showa Denko K.K (www.showa-denko.com); Soluble in water; There are two series: #100: it is an acidic solution used for non chemical amplified resists #300: it is a weak acidic solution and applicable for the both type of resist:
chemical amplified resists and non chemical amplified resists.
BUT WE DON´T HAVE IT AND IT IS RATHER EXPENSIVE ($1500 for 100mL).
Images fromRaith, 2008
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ESPACER 300 (Results from Raith)
insulator
resistconductive polymer
Optical Images; Additional spin coating step;
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Au on top as a conductive layer
Au
resist
glass substrate
front side Au
e-beam exposure
Au can be coated on top of resist to dissipate chargetypically 100A is sufficient (10nm)
Au must be deposited with Evaporation or SputteringElectron beam evaporation will expose resist
Au must be stripped with Potassium Iodine prior to resist development
Disadvantage: in somecase deposition of Aucan introduce electriccontamination on thesample
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Patterning by Critical Energy Electron Beam Lithography
In an e-beam system, the totalelectron yield, which is the sumof secondary electrons and thebackscattering electrons,changes as a function of theaccelerating voltage.
It is more intuitive that at highaccelerating voltages, an e-beam negatively chargesinsulators (σ<1).
But is less commonly know thatat LOW BEAM ENERGIES, thesurface can actually be chargedpositive (σ>1) when moreelectrons are ejected formsurface than stored itself.
AT A CRITICAL ENERGY, σequals unity, and a chargebalance between incoming andoutcoming electrons is satisfiedeven for isulator substrates.
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Patterning by Critical Energy Electron Beam Lithography
0,5keV 1,3keV 2,0keV
0,5keV 1,0keV 2,0keV
0,5keV 1,0keV 2,0keV
SPOT 2,0
SPOT 3,0
Referencearticle
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Patterning by Critical Energy Electron Beam Lithography
No distortions at E2= 1,3keV Charging effect at E= 5keV
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Patterning by Critical Energy Electron Beam Lithography
1kV e spot de 2,530kV e spot de 2,5
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Projeto Grafeno