Advanced resists for e-beam lithography: processing ... · M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/2015 5 Transferring patterns to the sample Etching (wet

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]


Processing Steps for Lithography

HardBake

DehydrationBake

AdhesionPromoter

ResistSpinning Pre-bake

ExposurePost-exposureBakeDevelopmentPlasma

Flash

Etching

Deposition(Lift-off)

Substrate cleaning


Lift-off (one monolayer)


Lift-off (bilayers - PMMA and PMGI)


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



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.



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.


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.


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


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


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);


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?


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


ESPACER 300 (Results from Raith)

insulator

resistconductive polymer

Optical Images; Additional spin coating step;


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


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.



0,5keV 1,3keV 2,0keV



SPOT 2,0

SPOT 3,0

Referencearticle



No distortions at E2= 1,3keV Charging effect at E= 5keV



1kV e spot de 2,530kV e spot de 2,5


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Advanced resists for e-beam lithography: processing ... · M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/2015 5 Transferring patterns to the sample Etching (wet