E SC 412 Nanotechnology: Materials, Infrastructure, and Safety … · 2018-05-06 · 50mTorr Si...
Transcript of E SC 412 Nanotechnology: Materials, Infrastructure, and Safety … · 2018-05-06 · 50mTorr Si...
Lecture 11 Outline
• Deposition Techniques
• Physical Vapor Deposition
• Chemical Vapor Deposition
• Electro-chemical Deposition
• Deposition Techniques in Nano-scaleI
Copyright 2014 by Wook Jun Nam
Physical Vapor Deposition (PVD)
• Evaporation
• Thermal
• Ebeam
• Sputtering
• DC Sputtering
• RF Sputtering
• Magnetron Sputtering
• Reactive Sputtering
• Pulsed laser deposition
Copyright 2014 by Wook Jun Nam
What happens on the deposition surface ?
Copyright 2014 by Wook Jun NamM. Ohring, The Materials Science of Thin Films, Academic Press, 2002
Evaporation: Typical Tool Configuration
J. D. Plummer, M. Deal, and P. D. Griffin, Silicon VLSI Technology Fundamentals, Practices, and Modeling , Prentice Hall, 2000
Copyright 2014 by Wook Jun Nam
Evaporation: Materials for a Heating Source
• Materials for heater:
− Vapor pressure of the materials should be very low
at the temperature where a source material is
evaporated.
− Should not react with a source material: (no source
material contamination or alloy formation with a
source material)
− Should not be outgassing at a evaporation
temperature
• Heater materials: refractory metals (e.g., W, Mo, Ta),
inert oxides or ceramic compound crucibles (e.g.,
Al2O3, B2O3, graphite, WC)
Copyright 2014 by Wook Jun Nam
Vapor Pressures of Elements
The source
material is heated
to the evaporation
temperature and
the evaporation
rate in g/s is given
by: Revap =
5.83x10-2
As(m/T)1/2 Pe
Copyright 2014 by Wook Jun NamM. Ohring, The Materials Science of Thin Films, Academic Press, 2002
Evaporation: Evaporation of Compounds
Single element is evaporated as an individual atom or atomic
cluster, but evaporation of compounds is more complex !
Needs separate sources
Copyright 2014 by Wook Jun NamM. Ohring, The Materials Science of Thin Films, Academic Press, 2002
Evaporation: Thermal vs. Ebeam
• Thermal evaporation:
− Has limitation in input power
− Has possible contamination from heater or crucible
Relatively low purity film deposition, and limitation in
material (no high meting temperature materials)
• Ebeam evaporation:
− Uses only small portion of a source material (less
possibility of contamination from a crucible).
− Can deposit materials with high melting points.
Copyright 2014 by Wook Jun Nam
DC Sputtering
Copyright 2014 by Wook Jun NamJ. D. Plummer, M. Deal, and P. D. Griffin, Silicon VLSI Technology Fundamentals, Practices, and Modeling , Prentice Hall, 2000
RF Sputtering
RF Sputtering: Self-Bias
Copyright 2014 by Wook Jun NamM. Ohring, The Materials Science of Thin Films, Academic Press, 2002
RF Sputtering (continued)
• Ideal for insulator sputtering (insulator target).
• Good ionization efficiency ( secondary electrons + electron
oscillations in plasma).
• Low process pressure.
Copyright 2014 by Wook Jun Nam
Increase Plasma Density
Charges feel force in electric and
magnetic fields. These fields can
be manipulated to control the
plasma density
Magnetron Sputtering
Copyright 2014 by Wook Jun NamM. Ohring, The Materials Science of Thin Films, Academic Press, 2002
Magnetron Sputtering (continued)
• Secondary electrons are trapped at the cathode, and it
increases ionization efficiency.
• High deposition rate.
• Low pressure operation.
• An erosion track on a target
• Nonuniform removal of particles from target may result in
nonuniform films deposition on a substrate.
Copyright 2014 by Wook Jun Nam
Sputtering Alloys
• Evaporation:
− Stoichiometry of film is different with that of source
because of different vapor pressures of elements
• Sputtering:
− Sputtering yields are different to each of the
elements.
− As a material with higher sputtering yield is
sputtered first, the target becomes a material with
lower sputtering yield rich.
− Due to the modified ratio on the target surface, the
stoichiometry of a film becomes similar to that of a
target.
− Sputtering of alloys needs a pre-sputtering
(conditioning) time to have steady state condition.Copyright 2014 by Wook Jun Nam
Reactive Sputtering
• Reactive sputtering is a process in which a metal is
sputtered in argon containing a small partial pressure of a
reactive gas such as O2 or N2.
• The active gas reacts with the metal atoms depositing on
the substrate to form a metal oxide or nitride film.
• It is a complex, challenging process that, if properly applied,
can result in very uniform, high-purity, insulating films.
• For best results: the gas's flow rate; total sputter pressure;
the reactive gas's partial pressure; and its mixing with the
argon near the substrate's surface are carefully controlled to
maintain proper stoichiometry in the depositing film.
Copyright 2014 by Wook Jun Nam
Reactive Sputtering (continued)
• A compound has better secondary
electron emission efficiency than a
metal, so as the target is covered by
the compound, the cathode voltage
is dropped rapidly (#2) since the
plasma impedance is dropped.
• As the reactive gas rate is decreased
and the metal target is exposed, the
cathode voltage is jumped back (#6)
• Reactive sputtering with a metal
target offers (1) easier and (2) more
pure film deposition than compound
target sputtering since the fabrication
of a compound target has more
possibilities of contamination.
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45
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Reactive Gas Flow
Ca
tho
de
Vo
lta
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Syste
m P
ressu
re
Copyright 2014 by Wook Jun Nam
Evaporation vs. Sputtering
Evaporation Sputtering
• Thermal energy
• Low E of evaporated atoms
or molecules: ~0.1 eV
• Hard to control deposited
film stoichiometry
• Highly directional
deposition & low E atoms:
poor step coverage
• Poor adhesion
• Ion bombardment
• High E of sputtered atoms
or molecules: 2~30 eV
• Relatively easy to control
deposited film stoichiometry
• Highly directional
deposition & high E atoms
or molecules: good step
coverage
• Good adhesion
• Ideal for deposition of alloy
and insulator
Copyright 2014 by Wook Jun Nam
50mTorr
Si Mold
Sputtering condition for nano-crater formation
Nano-pore
The breakage point
Layer A
Layer B
Si nano-cavity
Layer C
As the film thickness is getting
thicker the opening is closed
remining the void.
Thickness Monitor
• The crystal is coupled to an electrical circuit that
causes the crystal to vibrate at its natural (or
series resonant) frequency.
• A corresponding microprocessor based control
unit monitors and displays this frequency, and /or
any derived quantities, continuously.
• As the source material coats the crystal during
the deposition process, the resonant frequency
decreases in a predictable fashion, based on the
rate at which material arrives at the crystal, and
its density.
• The frequency change is calculated several times
per second, averaged, converted to a thickness
value via an algorithm stored in the
microprocessor and displayed as deposition rate,
in Angstroms per second.
• The accumulated coating over time is also
displayed, as the total thickness.
Copyright 2014 by Wook Jun Nam
http://www.tradekorea.com/products/qcm.html
Some Other PVD Techniques
• Pulsed Laser Deposition
Copyright 2014 by Wook Jun Nam
https://rt.grc.nasa.gov/main/rlc/pulsed-laser-deposition-laboratory/
Chemical Vapor Deposition (CVD)
• Atmospheric Pressure CVD (APCVD)
• Low Pressure CVD (LPCVD)
• Plasma Enhanced CVD (PECVD)
• Metal Organic CVD (MOCVD)
Copyright 2014 by Wook Jun Nam
Typical CVD Tool Configurations
J. D. Plummer, M. Deal, and P. D. Griffin, Silicon VLSI Technology Fundamentals, Practices, and Modeling , Prentice Hall, 2000Copyright 2014 by Wook Jun Nam
TRANSPORT and REACTION
Gas Transportation
J. D. Plummer, M. Deal, and P. D. Griffin, Silicon VLSI Technology Fundamentals, Practices, and Modeling , Prentice Hall, 2000Copyright 2014 by Wook Jun Nam
1) Transport of reactants by forced convection to the deposition region
2) Transport of reactants by diffusion from the main gas stream through the boundary
layer to the wafer surface
3) Adsorption of reactants on the wafer surface
4) Surface processes, including chemical decomposition or reaction, surface migration
to attachment sites, site incorporation, and other surface reactions
5) Desorption of byproducts from the surface
6) Transport of byproducts by diffusion through the boundary layer and back to the
main gas stream
7) Transport of byproducts by forced convection away from the deposition region
Steps in Chemical Vapor Deposition (CVD)
J. D. Plummer, M. Deal, and P. D. Griffin, Silicon VLSI Technology Fundamentals, Practices, and Modeling , Prentice Hall, 2000Copyright 2014 by Wook Jun Nam
Mass Transfer Limited Deposition
• Small hG
• Growth controlled by transfer
to substrate.
• hG is not very temperature
dependent.
• Common limitation at higher
temperatures
J. D. Plummer, M. Deal, and P. D. Griffin, Silicon VLSI Technology Fundamentals, Practices, and Modeling , Prentice Hall, 2000
Copyright 2014 by Wook Jun Nam
Surface Reaction Limited Deposition
• Small kS
• Growth controlled by surface
reactions (e.g., adsorption,
decomposition, surface
diffusion).
• kS is highly temperature
dependent (increases with T).
• Common limitation at lower
temperatures.
J. D. Plummer, M. Deal, and P. D. Griffin, Silicon VLSI Technology Fundamentals, Practices, and Modeling , Prentice Hall, 2000Copyright 2014 by Wook Jun Nam
Atmospheric Pressure CVD(APCVD)
Recently, used for a single
crystal Si layer deposition for
solar cell application !!
Advantages:
•High deposition rate
•Simple reactor
•High throughput
Disadvantages:
•Poor uniformity
•Poor step coverage
•Particle contamination
Copyright 2014 by Wook Jun Nam
https://www.dowcorning.com/content/etronics/etronicschem/etron
ics_newcvd_tutorial3.asp?DCWS=Electronics&DCWSS=Chemic
al%20Vapor%20Deposition
Low Pressure CVD (LPCVD)
(Process pressure: ~0.2 to 20
torr)
Advantages:
•Good film step coverage
•Excellent uniformity
•High purity film (low defects)
•Low particle contamination
Disadvantages:
•Lower (but reasonable)
deposition rate
J. D. Plummer, M. Deal, and P. D. Griffin, Silicon VLSI Technology Fundamentals, Practices, and Modeling , Prentice Hall, 2000
Copyright 2014 by Wook Jun Nam
Plasma Enhanced CVD(PECVD)
Plasmas are used to force
reactions that would not be
possible at low temperature.
Advantages.:
•Low deposition temperatures
•Fast deposition rate
•Good Step coverage
•Excellent uniformity
Disadvantages:
•Plasma induced damages
J. D. Plummer, M. Deal, and P. D. Griffin, Silicon VLSI Technology Fundamentals, Practices, and Modeling , Prentice Hall, 2000
Copyright 2014 by Wook Jun Nam
Metal Organic CVD(MOCVD)
• Also known as OrganoMetallic Vapor Phase Epitaxy
(OMPVE).
• Many materials that we wish to deposit have very low vapor
pressures and thus are difficult to transport via gases.
• One solution is to chemically attach the metal (Ga, Al, Cu,
etc…) to an organic compound that has a very high vapor
pressure (e.g., Trimethyl-gallium (TMGa), Trimethyl-indium
(TMIn))
• The organic-metal bond is very weak and can be broken via
thermal means on wafer, depositing the metal with the high
vapor pressure organic being pumped away.
Copyright 2014 by Wook Jun Nam
Metal Organic CVD(MOCVD)
Used for III-V technology,
some metalization
processes (W plugs and Cu)
Advantages.:
•Highly flexible—> can deposit
semiconductors, metals,
dielectrics
Disadvantages:
•HIGHLY TOXIC!,
•Environmental disposal costs
are high.
Copyright 2014 by Wook Jun Nam
http://britneyspears.ac/physics/fabrication/fabrication.htm
SiO2 grows much faster in an H2O
ambient than it does in dry O2
because the oxidant solubility in SiO2
is much higher for H2O than O2
Reaction at interface vs.
transport through the oxide
Thermal Oxidation
Copyright 2014 by Wook Jun Nam
J. D. Plummer, M. Deal, and P. D. Griffin, Silicon VLSI Technology Fundamentals, Practices, and Modeling , Prentice Hall, 2000
TEM of Si/SiO2 interface
Thermal Oxidation
Copyright 2014 by Wook Jun Nam
J. D. Plummer, M. Deal, and P. D. Griffin, Silicon VLSI Technology Fundamentals, Practices, and Modeling , Prentice Hall, 2000
A solution based deposition technique that is low cost, high throughput
and has excellent trench filling capabilities making this process ideal for
semiconductor interconnect deposition. A variety of metal salts available
for a broad range of deposition applications.
Electrochemical Deposition
Copyright 2014 by Wook Jun Nam
PVD Electroplated
Trench Filling PVD vs. Electroplating of Cu
Electrochemical Deposition
Copyright 2014 by Wook Jun Nam
Applied Materials SlimCell
ECP Technology
Electrochemical Deposition
http://www.appliedmaterials.com/technologies/library/raider-ecdCopyright 2014 by Wook Jun Nam
Applied Materials technology for Cu electroplating for sub-
65nm technology
Electrochemical Deposition
http://www.appliedmaterials.com/technologies/library/raider-ecdCopyright 2014 by Wook Jun Nam
• Good step coverage and filling capabilities
• Compatibility with dielectrics
• Produces strong, well textured films
• Low Cost
• High throughput
• Limited materials
• Seed layer required in many cases
• More difficult to control film morphology
Electrochemical Deposition :Pros & Cons
Copyright 2014 by Wook Jun Nam
Directional Deposition
• Highly ordered nano-element array structure is very
common architecture used in nano-devices due to its
unique advantages (e.g., high surface area to volume
ratio).
Copyright 2014 by Wook Jun Nam
Directional Deposition (continued)
• Photoresist needs to provide very high aspect ratio pattern
for selective dry etching.
• The high aspect ratio resist pattern can be collapsed due
to the capillary force during the development step.
Copyright 2014 by Wook Jun Nam
Directional Deposition (continued)
• Highly directional film deposition (poor step coverage) is
ideal for lift-off process.
Copyright 2014 by Wook Jun Nam
Thermal evaporation sputtering
Z. Cui, Nanofabrication: Principles, Capabilities, and Limits, Springer (2008)
Conformal Deposition
• In order to fill in the high aspect ratio of nano-cavity
patterns, a deposition method should offer extremely
conformal coating.
• Non-conformal coating creates a voids in a nano-cavity.
Copyright 2014 by Wook Jun Nam
Thermal evaporation sputtering
Z. Cui, Nanofabrication: Principles, Capabilities, and Limits, Springer (2008)
http://www.cambridgenanotech.com/cnpruploads/ALD%20Tutorial.pdf
Conformal Deposition (continued)
Copyright 2014 by Wook Jun Nam
Conformal Deposition (continued)
http://www.nature.com/nnano/journal/v6/n4/full/nnano.2011.12.html
• A lipid bilayer uniformly coated on nanopore membrane.
Copyright 2014 by Wook Jun Nam