Lift-off Electrolytic growth Etching transfer techniques Wet chemical etching Ion Beam Etching Reactive Ion Etching Reactive Ion Beam Etching

Transfer

techniques

Transfer techniques

• Lift-off

• Electrolytic growth

• Etching transfer techniques

• Wet chemical etching

• Ion Beam Etching

• Reactive Ion Etching

• Reactive Ion Beam Etching

• Chemical Ion Beam Etching

• High Density Plasma

Lift-off

deposition

Each process has his own technological requirements and his own limitations

Relevant:

Resist holding out during evaporation

Not relevant:

Resist sticking

Mechanical strength Resist height

Side wall profile

Etching using resist as a mask

Relevant:

Mechanical strength: selectivity

Not relevant:

Resist sticking

Thermal strength: selectivity

chemical or physical etching

Each process has his own technological requirements and his own limitations

Resist height

Electrolytic growth through resist

Each process has his own technological requirements and his own limitations

Relevant:

Holding against the chemical bath

Not relevant:

Mechanical strength

Resist sticking chemical bath

shaped material growth Resist height

Lift-off: deposition techniques

e -e -e -SiH4 CH4 He e -e -Plasma Arrivées de gaz (He, SiH4, CH4) Cathode et porte-substrat PRINCIPE DU PECVD

SCHEMA DE PRINCIPE DU DEPÔT PAR EFFET JOULE

0<U(V)<6 0<I(A)<400 Porte-substrat Susbstrat Cône d’évaporation Filament de tungstène Parcouru par un courant continu Anode Cathode Creuset et matériau à évaporer Cheminée

SCHEMA DE PRINCIPE DU DEPÔT PAR CANON A ELECTRONS

Ciblde métal Filament de Tungstène Aimant permanent

1.10-7_{<Pression de Travail (mbars)<1.10}-6

Bloc Canon Faisceau d’électrons Substrat

Porte-Substrat

SCHEMA DE PRINCIPE DE LA PULVERISTION CATHODIQUE RF MAGNETRON Ar+ Ar+ Ar+ Ar+ Ar+ Pression de travail 10-1_<P(Pa)<5 Porte-substrat Substrat Flux de matière Plasma Cible Aimant permanent (coupe); permet le confinement du plasma Porte-cible thermal evaporation e-gun deposition RF- sputtering PECVD

distance between the 2 depositions is adjusted

with the angle, according to:

Lift-off: angle evaporation

f

f

h

d

MMA/PMMA resist

suspended PMMA mask

weak molecular weight: huge under etch

Useful to made all metal devices with

tunneling junctions

Realization of "all-metal" devices (1)

Overlap (junction size) adjusted with angle

f

F. Pierre LPN

F. Pierre LPN U U V S

Realization of "all-metal" devices (2)

For only one lithography step, one can use:

• different metals

Realization of "all-metal" devices (3)

F. Pierre LPN SET Loop type circuit

junctions gate

Quantronium

Electrolytic growth: use of porous

media

Membrane

Pores

Anodic alumina template

200nm

Amorphous ion track etched polycarbonate membrane

Template dissolution

19.5 nm

UCL Louvain LPN

0 0.5 1 1.5 2 2.5 3 3.5 4 0 100 200 300 400 500 600 Time (s) I I II II III III Cathode (Pt) Anode (Pt) reference electrode Au cathode Membrane Electrolyte V A E Au Cathode Pores Membrane L = 22µm

Membrane after dissolution

20µm

20µm

18.4 µm

Nanowires after dispersion

5 µm

UCL Louvain LPN

Etching transfer techniques

4 main routes

• wet chemical etching

• isotropic plasma etching

• reactive ion etching (anisotropic)

• ionic etching

Main requirement: the size control!

The good achievement on the mastering of the control of the design rule for sub-micron structure requires the use of anisotropic etching techniques. Dry etching techniques like plasma ones are the

solution to the wet etching related problems except for the selectivity between mask and sample or

You may think to use under etching to reduce the size. Difficult to control because of surface state:

• strong etching (not sensitive to surface state) too fast • weak etching slow but too sensitive to surface state

Isotropic chemical wet etching

•Simple •Fast

Isotropic chemical wet etching:

selective over-etch of different materials

W InGaAs InP InAlAs GaAsSb InGaAs _Collector Emitter Base C. Dupuis LPN

The chemically controlled over-etch permits

to avoid short-cuts between contacts

LPN

Anisotropic wet etching

Uses of anisotropic etch rate with crystal face

Still some under etch

Uses to produce nice features over growth in

V-groves

Ion Beam Etching (IBE)

• Uses the impact of impinging ions _Ar

target surface

• Purely physical: linked to momentum exchange between particles

gas

accelerated ions

rotation anode

cathode

• Iionic ~ VT 3/2⇒low energy flux

• Neutral gazes: Ar, Xe, Ne, He • Sources (ex. Kaufmann)

ZUE

T∝

U binding energy of material Z atomic number of material E ion energy x coeff (angle)

• Sputtering rate T T E (eV) 1000 10-100 eV Implantation Threshold T 30 60 90 θ incident ion ejected atom θ

• Consequence of T=f(θ): mask faceting!

• Re-deposition + faceting: trenching effect •Quite slow •No selectivity •Re-deposition •Trenching •Damage •Clean •Easy control •Reproducibility

• Summary on ion beam etching, pros & cons:

Reactive Ion Etching (RIE)

Self Bias: few 100V

Chemically active ions -> volatile species

gas plasma C pump RF₁ RF₂ Planar configurations: RF1≠0, RF2=0 Isotropic plasma RF1≠0, RF2≠0 Triode RF1=0, RF2≠0 RIE

X

X

Self – bias V

dc

ion

µ

µ

_el

_ff

Plasma formation due to the difference between

the electron and ion mobilities in the gas.

ion

µ

µ

_el

≠

RF Vp -Vdc Vc Vdc=Vp-Vc Cathode: sample position time averaged reactor walls

potential values < Vp

(ionic hitting of the walls)

creation of a continuous self bias Vdc blocked by the capacitor C

⇒ this potential is responsible for the energy of the ions hitting the sample (extraction from plasma + acceleration across the dark depletion sheet)

Chemistry – Volatile species

Co, Co₂, H₂O, CF₄ O₂, CF₄ Photo-resists, Organics WF₆, TaF₆, NbF₆/WCl₆, TaCl₆, NbCl₆ CF₄, SF₆/Cl₂ W, Ta, Nb Ga(CH₃)₃, AsH₃, GaCl₂, GaCl₃ ... CH₄/H₂, Cl₂, SiCl₄… GaAs, III-V Al₂Cl₆, AlCl₃ BCl₃, Cl₂, CCl₄ Al SiF₄ CHF₃, CF₄, SF₆ SiO₂, Si₃N₄

SiF₄, SiCl₂, SiCl₄ CF₄, SF₆, NF₃, Cl₂ Si Volatile species Gas Material to be etched

Anisotropy:

lateral vertical

v

v

_ff

Over-etch control:

• chemistry

• pressure

• electrode polarization

The necessary ingredient to achieve

anisotropy is to add ion hitting to the

chemical plasma etching

e e e e Generation of etchant species Diffusion to surface Adsorption Reaction _Desorption Diffusion into bulk gas

Film

Gas species

One example: the Si case

Chemical adsorption

Chemical reaction

Desorption

F F F F F F F F

Si (F2)gas --> (F2)ads --> (2F)ads

Si + (4F)_ads --> (SiF₄)_ads

(SiF₄)_ads --> (SiF₄)_gas

F F F F Si F F F FSi Si

Anisotropy mechanisms: the ions

contribution

Surface defects are created by reactive ions :

• ions directivity

• etching enhanced on the unprotected surface

• etching inhibited on the edges

An etch inhibitor is adsorbed on the surface + ions directivity:

• destruction of surface inhibitor • edges are protected

• ex. of CH4/H2 polymer formation on the edges

Anisotropy achievement in the second case

passivation gas

Advantages of RIE

¾ Fast process ¾ Selectivity ¾ Anisotropy

¾ No re-deposition

¾ Use of passivation layer

¾Sensitive to pollution

¾Energy and pressure are linked

Summary for the RIE:

pros

&

cons

rotation

θ

Separation of the chemical & physical

parameters

Ions source and sample chamber are separated

Reactive gas: RIBE

Neutral gas: IBE, CAIBE

Addition of a reactive gas

in the sample chamber: CAIBE

RIBE: Reactive Ion Beam Etching

CAIBE: Chemically Assisted Ion Beam Etching

Reactive Ion Beam Etching: RIBE

¾ Same as IBE but with

chemically active ions

¾ Allows to separate the

physical/chemical action

SiO₂ or Si₃N₄

W

GaAs/AlGaAs resonant tunneling vertical quantum

boxes

InP Photonic Crystals

Φ=400nm h=1.2µm max Φ=0.94µm h=6.25µm Φ=350nm h=1.65µm L=25nm h=300nm L=30nm_h=450nm SOI photonic crystal

Some examples of RIE realizations

AlAs/GaAs micro-pillar 1 photon source

Examples RIBE

High Density Plasma (HDP) reactors

Helicon ICP Inductive coupling: helicon or ICP Microwave coupling: ECR

• high ion density

⇒faster process ⇒deeper etching

• ion energy controlled by bias • energy and density are

High density plasma (fast) with low energy (damage) Independent control of energy/density

Top down and bottom up?

Both techniques tend to the same dimension

Future of nanotechnology will be certainly a mixing of these techniques

Addressing of individual macromolecules Functionalization of substrates

FIB nano-machined substrate and gold cluster deposition

Cluster deposition on functionalized surfaces

LPN

LPN

Si patterning for selective deposition of

self-assembled nanoparticles produced

by chemical synthesis

50nm, 100nm, 150nm wide lines on 200nm thick PMMA Lines length 80µ_m

LPN

Pre-structuration of substrates for film

deposition

• Use of Si substrates • Thickness of the metal

compatible with the height of the structures

• PMMA (thickness ∼ 350nm) is directly used as an etching mask for the pattern transfer to Si

• Structure dimensions in the 100nm range with a pitch between them of 200nm. Etching depth : between 50 and 100nm

• "Large" area arrays : 3mm x 3mm

requested by NCRS –IMS and supplied for magnetic film deposition and characterization

LPN

Some results on large area arrays :

pillars

• Reactive ion etching is used to transfer the PMMA

pattern in the Si

• Chemistry, pressure and RF power are optimized in order to have an anisotropic

etching :

– Mixture of CHF₃ / SF₆ – Energy = 190V (15W) – Pressure = 10mT

LPN

Some results on large area arrays :

holes