e sc 412 nanotechnology: materials, infrastructure, and safety … · 2018-05-06 · 50mtorr si...

E SC 412

Nanotechnology: Materials, Infrastructure, and Safety

Wook Jun Nam

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

Top Down Approach


Deposition Techniques (Physical Deposition)


Physical Vapor Deposition (PVD)

• Evaporation

• Thermal

• Ebeam

• Sputtering

• DC Sputtering

• RF Sputtering

• Magnetron Sputtering

• Reactive Sputtering

• Pulsed laser deposition


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


Evaporation: Thermal Heating Source


Evaporation: Ebeam Heating Source

ebeam source


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)


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


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


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.


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


RF Sputtering (continued)

• Ideal for insulator sputtering (insulator target).

• Good ionization efficiency ( secondary electrons + electron

oscillations in plasma).

• Low process pressure.


Increase Plasma Density

Charges feel force in electric and

magnetic fields. These fields can

be manipulated to control the

plasma density

Magnetron Sputtering


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.


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.


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.

1

2

3

4

5

6

1

2

3

45

6

Reactive Gas Flow

Ca

tho

de

Vo

lta

ge

Syste

m P

ressu

re


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


50mTorr

Si Mold

Sputtering

Nano-pore

The breakage

points

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.


http://www.tradekorea.com/products/qcm.html

Some Other PVD Techniques

• Pulsed Laser Deposition


https://rt.grc.nasa.gov/main/rlc/pulsed-laser-deposition-laboratory/

Deposition Techniques

(Chemical Vapor Deposition)


Chemical Vapor Deposition (CVD)

• Atmospheric Pressure CVD (APCVD)

• Low Pressure CVD (LPCVD)

• Plasma Enhanced CVD (PECVD)

• Metal Organic CVD (MOCVD)


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


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)


Mass Transfer Limited Deposition

• Small hG

• Growth controlled by transfer

to substrate.

• hG is not very temperature

dependent.

• Common limitation at higher

temperatures



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.


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


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



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



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.


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.


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



TEM of Si/SiO2 interface

Thermal Oxidation



Deposition Techniques

(Electrochemical Deposition)


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


PVD Electroplated

Trench Filling PVD vs. Electroplating of Cu



Applied Materials SlimCell

ECP Technology


http://www.appliedmaterials.com/technologies/library/raider-ecdCopyright 2014 by Wook Jun Nam

Applied Materials technology for Cu electroplating for sub-

65nm technology


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


Deposition Techniques in Nano-scale


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).


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.


Directional Deposition (continued)

• Highly directional film deposition (poor step coverage) is

ideal for lift-off process.


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.


Thermal evaporation sputtering

Z. Cui, Nanofabrication: Principles, Capabilities, and Limits, Springer (2008)

http://www.cambridgenanotech.com/cnpruploads/ALD%20Tutorial.pdf

Conformal Deposition (continued)



http://www.chem.uci.edu/node/7218



http://www.nature.com/nnano/journal/v6/n4/full/nnano.2011.12.html

• A lipid bilayer uniformly coated on nanopore membrane.


Lecture 11 Outline

• Deposition Techniques

• Physical Vapor Deposition

• Chemical Vapor Deposition

• Electro-chemical Deposition

• Deposition Techniques in Nano-scaleI


e sc 412 nanotechnology: materials, infrastructure, and safety … · 2018-05-06 · 50mtorr si...

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