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
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
Outline
 Introduction
 Fundamental of sputtering
 Techniques of sputtering
 Sputtering zinc oxide thin film
 Summary
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
Outline
 Introduction
 Fundamental of sputtering
 Techniques of sputtering
 Sputtering zinc oxide thin film
 Summary
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
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
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
Sputter yield deposition
Sputtering
Ions are accelerated
into target
Some of the surface
atoms are sputtered
off of the target.
Measure of efficiency of sputtering
These sputtered
atoms “flow” acrossS  ejected atoms or molecules
incident ion
the chamber to
where they are
deposited
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.
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
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
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
Advantages & Disadvantages of sputter
deposition
Advantages
• 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.
Disadvantages
• 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.
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
Outline
 Introduction
 Fundamental of sputtering
 Techniques of sputtering
 Sputtering zinc oxide thin film
 Summary
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
DC (diode) Sputtering
The simplest sputtering technology
Parameters for DC Sputtering
Sputter voltage
typically -2 to -5 kV
Substrate Bias Voltage
http://www.glue.umd.edu/
~ddev/me489f/slides/2b_d
eposition_x6.pdf
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
E (e-) < 2eV - no ionization, elastic collisions only
E (e-) > 2eV - inelastic collisions add energy to Ar
 ionization (highest energy process, ~15eV)
changes with Ar pressure
increases with sputter yield
usually increases with high voltage
Note: mass (e-)/mass( Ar) ~ 10-5
• energy transfer small
• e- gain energy via elastic collisions until E>15eV for
ionization
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
Fundamentals of plasma sputtering
DC sputtering (diode sputtering)
Disadvantages:
• Low ion current density
(low sputtering rate)
Cathode
Voltage
~1.5 kV
• Electron
emission
+
• Sputtering
Ionisation coeffcient
Pressure
~10 Pa
noble gas
(e.g. Ar)
10
1
0.1
0.01
10
100
1000
Electron energy [eV]
• Implantation
• High working gas pressure
resulting in scattering (low
deposition rate)
• Defects
generation
Anode
+ substrate
Tomasz Suszko, International Student Summer School „Nanotechnologies in materials
engineering” Warsaw - Koszalin 2006
• Dielectric materials can not
be sputtered
• High voltage is needed
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
Fundamentals of plasma sputtering
(magnetron sputtering & unbalanced magnetron
sputtering)
Ionisation coeffcient
G.J. Mankey, Lecture 9, Univ of Alabama
10
+ Low working gas
pressure – 0.1 Pa
1
+ Very high ion current
density is possible (high
sputtering rate)
0.1
0.01
10
100
1000
Electron energy [eV]
Substrate
DC or pulsed
power supply
There is a possibility to control the
substrate ion current and the energy
of the ions as well
Tomasz Suszko, International Student Summer School „Nanotechnologies in materials
engineering” Warsaw - Koszalin 2006
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
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
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
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
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
Fundamentals of plasma sputtering
reactive sputtering
Compounds of the
target and gas elements
Inert gas (e.g. Ar)
Reactive gas (N2, O2, CH4 etc.)
Control unit
Optical signal
(optical emission spectroscopy)
For poorly conducting
or insulator deposits
pulsed power supply is
very usefull
•
•
•
•
Gas pressure
Gas flows
Discharge power
(Substrate bias –
energy of the ions)
• (Substrate ion
current density)
Pumping system
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
RF Sputtering
DC sputtering - what about dielectrics?
• in DC systems, positive charge builds up on the
cathode (target) need 1012 volts to sputter insulators !!
13.5 MHz RF Power Supply
(with matching network)
Magnet
Magnet
Cathode
avoid charge build up by alternating potential
Gas
In
Water Cooled
Target
RF sputtering
Sputtering
Dark
Space
Shield
Plasma
Ad-atom
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(5~30MHz)
Typically 13.56 MHz is used
Film growth
Substrate
Anode
Base plate
Hi Vac Pump
Rotary Pump
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
Ground
L
MiNa
ab.
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?itemid=11
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
Outline
 Introduction
 Fundamental of sputtering
 Techniques of sputtering
 Sputtering zinc oxide thin film
 Summary
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
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:
chamber
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.
monitor
Characterizations of sputtered sample:
Thickness of the sputtered films: spectroscopic
ellipsometry and dektak profilometry.
target
Transmittance: UV-VIS-NIR spectroscopy.
Crystal orientation: X-rays diffractometer.
Surface morphology : AFM
substrate
Resistivity: Hall measurement.
Mobility : Hall measurement.
Tri-Axis Semicore r.f. sputtering
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
X-rays diffraction spectra of sputtered Aldoped 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
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
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
Rudolf Research / AutoEL Shimadzu SolidSpe-3700 DUVnm/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.
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
Ar flow rate effect on the electrical
properties of Al doped ZnO film
Lakeshore 7704A Hall measurement
http://www.caeonline.com/listing/pro
duct/183090/lakeshore-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
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
Outline
 Introduction
 Fundamental of sputtering
 Techniques of sputtering
 Sputtering zinc oxide thin film
 Summary
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
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.
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.
Thank you for your attention…!!!
Student Presentation of FYS-9310 Material Science of Semiconductor, Oslo, May 29th, 2013
L
MiNa
ab.