Skryabina Olga 08.05.2020

Fabrication of nanostructures using thin films. Shadow mask evaporation technique vs. Etch technique.

Variations of shadow mask evaporation methods: Dolan bridge and bridge-free methods.Application of UV- and E-beam lithography.

Quality control and characterisation of non-epitaxial films.

Interfaces between metallic films. Problems and quality control.

Fabrication of nanostructures with artifitial nanoelements: nanotubes, nanowires, nanocrystals etc.

Substarte preprocessing, artificial elements deposition, selection of suitable elements.

Fabrication of nanostructures using UV and E-beam lithography.

0D nanostructures1D nanostructures2D nanostructures

3D nanostructures

Features of the nanoworld

Fabrication

0. * Artificial components preparation

1. Lithography

2. Material evaporation

3. Etching

Lithography principle

Oil = polymer resist

Ink = metal layer

Si

SiO2

Doped

E-beamλ = 0.001 – 1 nm~ 10 нм

X-rayλ = 0.4 – 5 nm~ 15 нм

UVλ = 250 – 400 nm~ 200 нм

FIB~ 10 нм

Imprint~ 30 нм

Scanning Probe~ atom

Photo/electron resist

Exposure

Cr sputtering

Development

Etching

Resist removal

Photomask production

Photomask – metal «static» layerE-beam mask – resist «dynamic» layer

Substrate preparation Clean and dry

Coating 1000 – 6000 rpm, 30-60 s, 0.02 – 4 mkm

Tempering, solvent removal 120 oC - 10 min, 150oC - 5 min, etc.

E-beam exposure 30 kV, 500 mkC/cm2

Development 2-4 min, Stopper - IPA

Specific technologies Magnetron sputtering, thermal evaporation, etching

Removal Acetone

Lithography resists

Positive Negative

Lift-off processes Etching processes

Exposure

Result

Depolymerisation Polymerisation

Resist

Mask

Metal

SiO2

Yellow light

Image-reversal resistUndercut (Lift-off) profile

Positive resistOvercut profile

Lithography resists

Hirokazu ITOICEP-IAAC 2015 Proceedings

Example of the Lift-off profile

Example: PMMA (polymethyl methacrylate).

Applications:• High resolution resist• Wafer coating• Bonding adhesive layer

Composition:1. The radiation sensitive component2. Film-forming polymers to ensure the viscosity3. Solvents for uniform distribution of all components

Lithography resists

(thermionic emission)

E-beam lithography

The main elements of EL lithograph

• Vacuum system, P < 10-4 mbar

• E-beam source (W, LaB6, ZrO)

• An electrostatic or electron-magnetic type blanking unit

• The deflection unit - either combined with the end lens, or mixed after it.

• The block of dynamic focus, correcting aberrations introduced by the deviation of the beam from the optical axis of the system.

• An electron detection system that signals the detection of alignment marks and other details of the target's relief.

• Precision working table with a mechanical drive that provides processing of the entire plate.

R = λ / 2 NA

Incident electrons

Secondary electrons

Proximity effect

E = 1

E = 1/2E = 1/4Internal proximity effect Underexposure

External proximity effect Overexposure

Further developments depend on your plansOn structure you want to make

Structure types

Sandwich Planar

Artificial objects

Sandwich structures

Stolyarov Thesis

• A lot of iterations, a lot of layers

• Layer alignment

• Metal deposition with vacuum cycle break

• Using any material

• An error at any stage entails a repeat

of the entire large cycle anew

Golikova Thesis

Planar structures

• A few iterations

• Virtual calculation before the processing

• Metal deposition without vacuum cycle break

• In some cases, it is impossible to evaporate

a superconductor and a ferromagnet onto one structure

• Size limit

Shadow mask evaporation methods: Dolan bridge

Shadow mask evaporation methods: Dolan bridge

Planar structures

Bridge-free technique (BFT)

BFT is based on the control of strongly asymmetric undercuts in a bilayer resist.By adjusting the undercut position and its depth, we select for each angle of evaporation whether the metal will be depositedonto the substrate or on the resist wall which will be removed after lift-off. In this way we can control which wire will be connected to the junction.

J-D. Pillet

Shadow evaporation example

Quality control and characterisation of non-epitaxial films

1. SEM – grain control2. Compound control. Mass-spectrometry3. Conductivity, RRR4. Tc (for superconductors)

Artificial objects

• A few iterations

• Meticulous preparation

• Sample preparation with vacuum cycle break

• Using any material

• Success depends on the quality

of the artificial object

NANO

Nanoclasters

Size 1-5 nm,104 atoms

Nanoparticles

Size 5-100 nm103 - 108 atoms

Сolloidal systems = precursors of nanosystems

Step 1Structures creation

Ways to obtain nanomaterials

Bottom-upassembly

VLS (Vapor-Liquid-Solid)

On-Off method

Hydrothermal synthesis

Up-bottomdisassembly

Mechanical grinding

Sonochemistry

Laser ablation

PVD (Physical Vapor Deposition)

CVD (Chemical Vapor Deposition)

Electrodeposition

Magnetron sputtering

OFF–ON method (on-film formation of nanowires) - the driving forces

behind the growth of NW are residual compressive stresses induced by

the difference between thermal expansion coefficients of metal and

oxidized silicon. Root growth.

The main disadvantage of the OFF-ON method is the need for heating and

prolonged exposure of the film at high temperatures (which is very close to

the melting point of 271.3 ° C) and the difficulty in obtaining the necessary

composites

W. Shim et al, Nano Lett. 9, 18 (2009)

Radio frequency (RF) magnetron sputtering on a substrate while heating. Tip

growth.

Nanowires’ growth occurs with the participation of screw dislocations to diffusion of metal

adatoms to the tip of the growing nanowire.

Substrate effect

Transition metal films (Fe, Ni, and Co) oxidized Si, Si (111) oxidized Si (100)

fused quartz W, Pt, and Au on oxidized Si. The mechanism of nanowires growth is

proposed, in which the formation of a fine grained polycrystalline Bi film with the preferential

grains and hillocks crystallographic surface orientation [particularly (110)] plays a decisive

role.

S. Cao et al, Solid State Comm. 149, 87 (2009)V. T. Volkov et al, Appl. Phys. A 123:503 (2017)

The actual concentration of the components is higher than the equilibrium concentration To achieve minimum free energy of the alloy system

ПЖК-метод синтеза нанопроволок

satiationliquid alloy

Solid structure

Vapor–Liquid–Solid Growth

K.K. Lew et al, Adv. Mater. 15, 2073 (2003) .

Chemical vapor deposition (CVD)

For graphene - methane gas.

Metal particles are catalyst for growth.

The carbon formed during the thermal decomposition of a

hydrocarbon dissolves in the metal nanoparticle. When a

high concentration of carbon in the particle is reached, an

energetically favorable “release” of excess carbon in the

form of a distorted half-fullerene cap occurs on one of the

faces of the catalyst particle.

Hydrothermal synthesis

Yuxin Zhao et al, New J. Chem., 2012, 36, 130–138

The method is based on the ability of water and aqueoussolutions to dissolve at high temperatures and pressuresubstances that are practically insoluble under normalconditions.

Physical vapor deposition (PVD)

High quality, high-performance solid materialsVacuum/inert gas

Superfluid helium and vortex filaments. Laser ablation.

T = 4.2 K = He-I phase - the boiling point of liquid He-4 at atmospheric pressure.

T = 2.177 K = He-II phase - superfluid helium (at saturated vapor pressure).

According to the Onsager – Feynman hypothesis, when a He-II perturbation

occurs in the superfluid component, vortex filaments can arise.

Any impurity suspended in superfluid helium have an affinity for the

quantized vortex. The particle tends to fit along the axis of the vortex, since

the energy of a particle with finite viscosity is inimal in the core of the

vortex.

Entering a substance into liquid helium using laser ablation.

The laser pulse evaporates the target material, at the same time creating a

perturbation in the volume of superfluid liquid helium — a necessary

condition for the onset of quantum vortices.

IPMT RAS Karabulin A.V. et al, Chemical Physics Letters, 519–520, 64–68 (2012)

Template-assisted technology

Conditions for templatesChemical stability

Mechanical strength

Diameter, density and uniformity of pores

Types of templates

Anodic Aluminium Oxide

Polycarbonate (PC) Membranes

Nano-channel glass

Technologies

• Injection of the conducting melt into nanochannel insulating plates (P=102 атм)

• Electrochemical deposition (mono- and polymetallic)

• Pressure injecting metal liquid melt (Possibility to obtain composite materials)

Aluminum surfacepolishing

First oxidation

Oxide film dissolution

Second oxidation

Al dissolution

Barrier layer removal

Increase in pore diameter

Au contact deposition

Elecrodeposition

AAO Template fabrication

PdNi alloy

Ag structures

Pulse current electrodeposition

DC current electrodeposition

Step 2Quality control

Quality control

Optical microscopy!

Quality control

Studing the topography of defect heterogeneities and surfaceconditions

- the surface topology (grain boundaries, pores, cracks, composition inhomogeneities, etc.) – in reflected orsecondary electrons

- distribution of elemental composition over the surface ofthe sample — in characteristic x-ray radiation, Auger electrons

- topography of the magnetic domain structure – insecondary electrons

- etc.

Electron beam instruments

Scanning electron microscopy (SEM)

- the surface topology (grain boundaries, pores, cracks, composition inhomogeneities, etc.) – in reflected orsecondary electrons

Li et al, Ultramicroscopy, 184, Part A (2018)

Transmission electron microscopy (TEM)

Sample thickness ∝ λe

InformationExcitation

Photons Electrons Ions

Photons XRF(X-ray fluorescence)

XES (X-ray

emission spectroscopy)

XIS (X-ray ion spectroscopy)

Electrons XPS(X-ray photoelectron spectroscopy)

AES(Auger electron spectroscopy)

AIS(Auger ion spectroscopy)

Ions LDMS (direct laser

desorption mass-spectrometry)

SMS (spark mass-

spectrometry)

SIMS (secondary-

ion mass-spectrometry)

Surface analysis (*several atom layers)

• Atom ionization by external radiation (x-ray, fast electrons, ions)with the formation of a vacancy on one of the inner energylevels. This state of the atom is unstable.

• Vacancy is filled with an electron of one of the overlying atomicenergy levels. The energy can be emitted as a quantum of x-rayradiation, or could be transferred to a another electron, which asa result flies out of the atom – Auger effect is observed.

- distribution of elemental composition over the surface ofthe sample — in characteristic x-ray radiation, Auger electrons

MagneticQuadrupoleTime of flight (TOF)Ion cyclotron resonanceEtc…

• Molecules ionization in ionization source

• The resulting ions are removed by the electric field andfocused into the beam. Neutral molecules are removed by a vacuum pump.

• The stream of accelerated ions enters the mass analyzer, where the ions are separated by mass

• Separated ion beams fall into the detector, where the ioncurrent is converted into an electrical signal, which isamplified and recorded

Surface analysis

Mass spectrometer (analyzer)

Quality control

- topography of the magnetic domain structure - in secondaryelectrons

The physical basis of SEMPA microscopy is the fact that secondary electrons emitted by a sample under the influence of a beam of primary electrons have spin polarization, which is associated with the spin density in the material.

The spin density directly reflects the distribution of magnetization in the sample.

Step 3First preparations

Chip preparation: Global/local marks

Structures’ design (Soft: AutoCAD, DraftSight)

Step 4Fabrication

Structure design + global/local marks

Resist selection based on metal thickness

Dose test (? μC/cm2)

Thickness metal calibration

“Empty tests”

“Tactical” sample

Processing