Deposition of thin films by sputtering method

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Student Presentation of FYS-9310 Material Science
of Semiconductor
Deposition of thin films by sputtering method
Feri Adriyanto
PhD student Microsystems and Nanotechnology
Laboratory Department of Physics, University of
Oslo
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Outline

• Introduction

• Fundamental of sputtering

• Techniques of sputtering

• Sputtering zinc oxide thin film

• Summary

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Outline

• Introduction

• Fundamental of sputtering

• Techniques of sputtering

• Sputtering zinc oxide thin film

• Summary

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Mechanism of sputtering ?
Interactions of ions with surfaces
The ion impact may set up a series of collisions
between atoms of the target, possibly leading to
the ejection of some of these atoms. This
ejection process is known as sputtering.
The removal of surface atoms due to energetic
particle bombardment
http//www.postech.ac.kr/mse/tfxs/2003_2/chapter3.
pdf
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Sputter yield deposition
Sputtering Ions are accelerated into target Some
of the surface atoms are sputtered off of the
target. These sputtered atoms flow across the
chamber to where they are deposited
Measure of efficiency of sputtering
The sputter yield depends on (a) the energy of
the incident ions (b) the masses of the ions and
target atoms (c) the binding energy of atoms in
the solid and (d) the incident angle of ions.
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Sputtering Alloy Targets

• Slow diffusion mixing in solids (sputtering)
• target reaches steady state
• surface composition balances sputter yield

Suiqiong Li, student presentation of ELEC 7730
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Advantages Disadvantages of sputter deposition
Disadvantages
Advantages

• Sputtering rates are low compared to those that
  can be attained in thermal evaporation.
• Sputtering targets are often expensive and
  material use may be poor.
• Most of the energy incident on the target becomes
  heat, which must be removed.
• In reactive sputter deposition, the gas
  composition must be carefully controlled to
  prevent positioning the sputtering target.

• Elements, alloys and compounds can be sputtered
  and deposited.
• The sputtering target provides a stable,
  long-lived vaporization source.
• In some configurations, reactive deposition can
  be easily accomplished using reactive gaseous
  species that are activated in plasma.
• The source and substrate can be spaced close
  together.
• The sputter deposition chamber can have a small
  volume.

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Outline

• Introduction

• Fundamental of sputtering

• Techniques of sputtering

• Sputtering zinc oxide thin film

• Summary

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DC (diode) Sputtering
The simplest sputtering technology
Parameters for DC Sputtering
Sputter voltage typically -2 to -5 kV Substrate
Bias Voltage substrate is being bombarded by
electrons and ions from target and plasma
sputtering film while you deposit neutral atoms
deposit independently put negative bias on the
substrate to control this can significantly
change film properties Deposition rate changes
with Ar pressure increases with sputter yield
usually increases with high voltage
http//www.glue.umd.edu/ddev/me489f/slides/2b_dep
osition_x6.pdf

• E (e-) lt 2eV - no ionization, elastic collisions
  only
• E (e-) gt 2eV - inelastic collisions add energy to
  Ar
• ionization (highest energy process, 15eV)
• Note mass (e-)/mass( Ar) 10-5
• energy transfer small
• e- gain energy via elastic collisions until
  Egt15eV for ionization

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Fundamentals of plasma sputtering DC sputtering
(diode sputtering)
Tomasz Suszko, International Student Summer
School Nanotechnologies in materials
engineering Warsaw - Koszalin 2006
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Fundamentals of plasma sputtering (magnetron
sputtering unbalanced magnetron sputtering)
G.J. Mankey, Lecture 9, Univ of Alabama
There is a possibility to control the substrate
ion current and the energy of the ions as well
DC or pulsed power supply
Substrate
Tomasz Suszko, International Student Summer
School Nanotechnologies in materials
engineering Warsaw - Koszalin 2006
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Advantages Disadvantages of Magnetron Sputtering
Advantages
High deposition rate Reducing electron
bombardment of substrate Extending the operating
vacuum range ability to operate at lower pressures
The most widely commercially practiced sputtering
method
Disadvantages

• An erosion track in the target
• his leads to poor efficiency of sputtering yield
  versus target volume compared to non-magnetron
  sputtering
• Non-uniform removal of particles from target
  result in non-uniform films on substrate

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Reactive Sputtering

• Sputtering metallic target in the presence of a
  reactive gas mixed with inert gas (Ar)

A mixture of inert reactive gases used for
sputtering
oxides Al2O3, SiO2, Ta2O5 (O2) nitrides TaN,
TiN, Si3N4 (N2, NH3) carbides TiC, WC, SiC
(CH4, C2H4, C3H8)
chemical reaction takes place on substrate and
target can poison target if chemical reactions
are faster than sputter rate adjust reactive gas
flow to get good stoichiometry without
incorporating excess gas into film
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Fundamentals of plasma sputtering reactive
sputtering
Compounds of the target and gas elements
Inert gas (e.g. Ar) Reactive gas (N2, O2, CH4
etc.)
For poorly conducting or insulator deposits
pulsed power supply is very usefull
Pumping system
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RF Sputtering

• DC sputtering - what about dielectrics?
• in DC systems, positive charge builds up on the
  cathode (target) need 1012 volts to sputter
  insulators !!
• avoid charge build up by alternating potential

RF sputtering
frequencies less than about 50 kHz electrons and
ions in plasma are mobile both follow the
switching of the anode and cathode basically DC
sputtering of both surfaces frequencies above
about 50 kHz ions (heavy) can no longer follow
the switching enough electrons to ionize
gases(530MHz) Typically 13.56 MHz is
used
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Advantages of RF Sputtering
It works well with insulating targets High
efficiency easier to keep plasma going ? can
operate at lower Ar pressures (1-15 mTorr) ?
fewer gas collisions ? more line of sight
deposition
http//aultimut.com/aultimut/details.asp?itemid11
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Outline

• Introduction

• Fundamental of sputtering

• Techniques of sputtering

• Sputtering zinc oxide thin film

• Summary

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Al-doped ZnO thin films for TCO applications
Sample Prepared The ZnO thin films were
deposited onto glass and n-Si (100) substrate
with Tri-Axis Semicore r.f. sputtering machine
using 5 Al-doped ZnO target. Experimental
conditions Substrate temperature 4000 C. Ar
flow-rate 30 sccm, 50 sccm, 60 sccm, 70 sccm and
80 sccm. r.f. power 50 W and 200
W. Characterizations of sputtered
sample Thickness of the sputtered films
spectroscopic ellipsometry and dektak
profilometry. Transmittance UV-VIS-NIR
spectroscopy. Crystal orientation X-rays
diffractometer. Surface morphology
AFM Resistivity Hall measurement. Mobility
Hall measurement.
chamber
monitor
target
substrate
Tri-Axis Semicore r.f. sputtering
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X-rays diffraction spectra of sputtered Al-doped
ZnO thin films
AFM Dimension 3100 at SMN UiO

• A strong X-ray peak from (002) and (004) planes
  is dominant, suggesting that most grains have
  c-axis perpendicular to the substrate surface.
• The (002)-ZnO and (004)-ZnO peaks were measured
  at 2? 34.120, and 71.850

Bruker AXS D8 Discover
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Effect of sputtering power on the growth rate and
transmittance at 480 nm

• Growth rate of the Al-doped ZnO thin films
  increases nearly linearly from 1.0 to 5.4 nm/min
  when the sputtering power increases from 50 to
  200 W
• As the sputtering power increases from 50 to 150
  W, the transmittance at 480 nm increases firstly
  from 83 to 92 and then decreases to 80. The
  maximum transmittance of 92 was obtained at the
  sputtering power of 150 W.

Rudolf Research / AutoEL
Shimadzu SolidSpe-3700 DUV
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Ar flow rate effect on the electrical properties
of Al doped ZnO film
Lakeshore 7704A Hall measurement
http//www.caeonline.com/listing/product/183090/la
keshore-7704a

• The resistivity of the films is decreases as the
  Ar flow rate is increased. The lowest resistivity
  of 9.74 x 10-4 ?.cm was obtained at the films
  with Ar flow rate of 80 sccm.
• The mobility increases with the Ar flow rate
  increases.
• The carrier concentration also indicates the same
  pattern as the mobility

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Outline

• Introduction

• Fundamental of sputtering

• Techniques of sputtering

• Sputtering zinc oxide thin film

• Summary

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Summary

• Sputter deposition, also known as physical vapor
  deposition is a widely used technique for
  depositing thin films on semiconductor wafers.
• The range of applications of sputtering and the
  variations of the basic process, is extremely
  wide.
• ZnO thin films have been successfully deposited
  by rf sputtering and a promising transparent
  conductive oxide for application in thin film
  solar cells.

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Thank you for your attention!!!