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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