Towards quantitative modelling of
magnetron sputter deposition
D. Depla
Dedicated Research on Advanced Films and Targets
Ghent University
Crash course
The processes
The model
The parameters
Examples
Conclusions
Magnetron sputtering: components
A magnetron discharge is a magnetically enhanced glow discharge. Key components
are the magnets located below the cathode.
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
1
1
Crash course
The processes
The model
The parameters
Examples
Conclusions
Magnetron sputtering : the discharge
Simulation of an electron
trajectory above a
cylindrical magnetron
Schematic of the electron
movement above a planar
magnetron, showing the
hopping of the electron on
the target, and the path
defined by the ExB drift.
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
Examples
www.DRAFT.ugent.be
2
Conclusions
Magnetrons
Planar magnetrons : target usage
23%
Optimalisation of the magnet configuration
46%
65- 90%
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
3
2
Crash course
The processes
The model
The parameters
Examples
Conclusions
Reactive magnetron sputtering
Together with the
pressure change,
we notice changes
in discharge
voltage and
deposition rate.
And who would
care if the
deposition rate
stayed constant?
Metallic mode
High deposition rate
No fully oxidized layers
D. Depla
Crash course
Reactive mode
Low deposition rate
Fully oxidized layers
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
Examples
www.DRAFT.ugent.be
4
Conclusions
The processes
The processes
Sputtering
Chemisorption
Knock on and direct implantation
(Re)deposition
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
5
3
Crash course
The processes
The model
The parameters
Examples
Conclusions
Sputtering (1)
A strong need for sputter yields not only for oxides but also for metals.
Measuring the mass difference
and discharge current
at constant discharge voltage
Quantification of target erosion/deposition rate
Difficulties
1. Electron yield
2. Neutrals
3. Ion energy (see fion)
On the effective sputter yield during magnetron sputter deposition
D. Depla NIMB 328 (2014) 65
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
www.DRAFT.ugent.be
Examples
6
Conclusions
Sputtering (2)
For oxides : data has been
obtained for Y2O3 and Al2O3
See later…
Neutrals
Charge exchange mechanism
Window based on literature
I.Y. Burmakinskii et al.
Tech. Phys., 49 (1) (2004), pp. 119–122
E. Bultinck, et al., New J. Phys., 11 (2009)
Consistent with advanced simulations
E. Bultinck, et al., New J. Phys., 11 (2009)
M.J. Goeckner, J.A. Goree, T.E. Sheridan
IEEE Trans. Plasma Sci. 19 (1991), 301–308
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
7
4
Crash course
The processes
The model
The parameters
Examples
Conclusions
Chemisorption : target (1)
After exposing the target to oxygen
the target is sputter cleaned.
The sputter cleaning time allows to
calculate the thickness.
discharge on
800
0.4
Discharge voltage (V)
0.5
0.3
600
0.2
400
0.1
200
0
-200
-400
0.0
Discharge current (A)
1000
-0.1
power supply on
stable
discharge
discharge current
-0.2
discharge voltage
current
-0.3
600
800
1000 1200
time after the start of the recording (ms)
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
Examples
www.DRAFT.ugent.be
8
Conclusions
Chemisorption : target (2)
Good agreement with literature on the
oxidation rate
So, no influence of the bombardment
prior to the oxygen exposure
But the plasma does not contain only O2.
See later…
This story however shows another
important message.
C. Palacio, J.M. Martinez-Duart Thin Solid Films 90 (1982), 63–67
J.M. Sanz, S. Hofmann, J. Less-Common Met. 92 (1983), 317–327
P.B. Sewell, D.F. Mitchell, M. Cohen, Surf. Sci. 29 (1972) 173–188
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
9
5
Crash course
The processes
The model
The parameters
Examples
Conclusions
Chemisorption : target (3)
How clean is a target during sputtering?
R. Schelfhout, K. Strijckmans, F. Boydens, D. Depla
Applied Surface Science 355(2015)743-747
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
Examples
www.DRAFT.ugent.be
10
Conclusions
Chemisorption : substrate (1)
Method :
Amount in the layer
In corporation coefficient =
Amount arriving
# depositions at same conditions
Mass Spectrometry
oxygen flow
at the position of the substrate
argon pressure
under the same conditions as the depositions
pumping speed
discharge current
T-S distance
chamber geometry
# depositions WITH fixed, small oxygen flow
# depositions WITHOUT fixed oxygen flow
to account for the background gases
EPMA
W.P. Leroy, S. Mahieu, R. Persoons, D. Depla
Thin Solid Films 518 (2009) 1527
W.P. Leroy, S. Mahieu, R. Persoons, D. Depla
Plasma Processes and Polymers 6 (2009) S342
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
11
6
Crash course
The processes
The model
The parameters
Examples
Conclusions
Chemisorption : substrate (2)
Aluminium
Yttrium
T-S distance
15 cm
T-S distance
8cm
Ar pressure
0.34 Pa
Ar pressure
0.34 Pa
O2 /Ar
1.5/20
O2 /Ar
1/20
Idischarge
0.47 A
Idischarge
0.47 A
peff
5.26 x 10-4 Pa
± 0.44 x 10-4 Pa
peff
5.54 x 10-5 Pa
± 1.15 x 10-5 Pa
α
0.107
± 0.032
α
0.230
± 0.043
T-S distance
10cm
T-S distance
15cm
Ar pressure
0.34 Pa
Ar pressure
0.34 Pa
Magnesium
Copper
O2 /Ar
2.9/20
O2 /Ar
1.5/20
Idischarge
0.47 A
Idischarge
0.47 A
peff
2.53 x 10-4 Pa
± 0.67 x 10-4 Pa
peff
1.57 x 10-2 Pa
± 0.75 x 10-2 Pa
α
0.170
± 0.067
α
0.0046
± 0.0003
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
www.DRAFT.ugent.be
Examples
12
Conclusions
voltage
V
O2
V
oxAr
V
Ar
status
argon
status
Oxygen
status
Knock-on and direct implantation
magnetron
time
A similar scheme as for chemisorption on the
target, but now the target is oxidized by
exposure to an oxygen plasma.
∆t
This time scale is only
understandable when oxygen is
implanted.
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
13
7
Crash course
The processes
The model
The parameters
Examples
Conclusions
8.3
7.3
6.4
5.5
4.6
3.7
2.8
1.8
0.9
0
monolayers
Knock on and direct implantation
We assume that all nitrogen is
bonded to titanium.
The calculated thicknesses fit
nicely with implantation range of
nitrogen ions into titanium at
energies defined by the discharge
voltage
Guttler D, Abendroth B, Grotzschel R, Moller W, Depla D
Applied Physics Letters 85 (2004) 6134
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
Examples
www.DRAFT.ugent.be
14
Conclusions
(Re)deposition
SIMTRA is particle trajectory code.
New
version
with
improved
GUI
is
available … for free
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
15
8
Crash course
The processes
The model
The parameters
Examples
Conclusions
(Re)deposition
The fraction of sputtered
material returning to the
target scales almost linearly
with the argon pressure.
D. Depla
Crash course
Target redeposition is high in the racetrack
but this is not important as it is balanced by
the erosion process. However outside the
racetrack oxide formation will occur.
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
Examples
www.DRAFT.ugent.be
16
Conclusions
The model
The model
Target description
Substrate description
How to use the model ?: GUI
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
17
9
Crash course
The processes
The model
The parameters
Examples
Conclusions
Target description
The transport is defined by
sputtering and redeposition
As we know ions get
implanted, we describe
the ion implantation in
the bulk
Initially the implanted
atoms
are
not
chemically bonded. We
describe explicitly the
chemical reaction
knrnm
Surface processes are described as
a balance between removal and
addition
D. Depla
K. Strijckmans and D. Depla
Journal of Physics D: Applied Physics 47 (2014) 235302
1st EUCASS Aerospace Thematic Workshop
Crash course
The processes
The model
The parameters
www.DRAFT.ugent.be
Examples
18
Conclusions
Target surface description
Derivation based on conservation of particles M and MRz
One example
metal
compound
chemisorbed oxygen
Transport
Chemisorption
Sputtering
knock-on
Redeposition
Redeposition
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
19
10
Crash course
The processes
The model
The parameters
Examples
Conclusions
Substrate condition
metal
compound
chemisorbed oxygen
Similar story for the substrate
RSD2013= critical revision of RSD2009
• Two discrete layer + subsurface
• Saturation limit
• Redefining surface equations
Simulations are possible in steady-state and time
Multi-cell approach for both target and substrate
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
www.DRAFT.ugent.be
Examples
20
Conclusions
“The Chinese menu card” approach
Solution:
D. Depla
Steady
Uniform
deposition
C,D,E
No redeposition
Time
A,B
Deposition
profile
C,D,E
A,B
Uniform
deposition
D,E
A,B,C
Redeposition
D,E
A,B,C
No redeposition
Uniform current
B,C,D,
E
A
Non-uniform
current
B,C,D
,E
A
Uniform current
No saturation
limit
E
A,B,C,
D
Saturation limit
E
A,B,C
,D
No saturation
limit
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
21
11
Crash course
The processes
The model
The parameters
Examples
Conclusions
Running RSD2013
Command line
Graphical user interface (GUI)
Manual
Free download
download SRIM
www.srim.org
download SIMTRA
www.DRAFT.ugent.be
download RSD2013
www.DRAFT.ugent.be
K. Strijckmans and D. Depla
Journal of Physics D: Applied Physics 47 (2014) 235302
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
Examples
www.DRAFT.ugent.be
22
Conclusions
The parameters
The parameters
What do we know ?
What we don’t know !
Fitting experiments
What can we learn ?
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
23
12
Crash course
The processes
The model
The parameters
Examples
Conclusions
Input parameters : the quest
Problem: 2 unknown parameters (αt, k)
Reason: experimentally or by simulation hard to retrieve (even for Yc)
Goal: fit freedom and material dependency
Solution: fitting RSD model to experiments
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
www.DRAFT.ugent.be
Examples
24
Conclusions
Experimental setup
Sputter conditions:
• Target Al or Y (D = 2”)
• Process gas Ar
• Reactive gas O2
•S = 55 L/s or 112 L/s
• Pbase = ~10-4 Pa
• PAr = 0.45 Pa or 0.37 Pa
• I = 0.4 A, 0.5 A or 0.6 A
Hysteresis experiment =
stepwise in/decreasing the O2 flow
while collecting
steady state values V, I and Ptot
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
25
13
Crash course
The processes
The model
The parameters
Examples
Conclusions
Fitting procedure
Fit criteria = 6 critical O2 flow values
• goodness of the fit = worst match out of 6
• fits are ‘good’ if critical points fall within acceptance tolerance fa
(=experimental resolution)
Simulation includes
measured V and I variation
changing target oxidation
D. Depla
Crash course
Ym and Iion
oxygen implantation profile
Iion (by YSEE)
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
www.DRAFT.ugent.be
Examples
26
Conclusions
Scan algorithm
Serial implementation
illustrated for a 2-D
parameter space
(X,Y)
Goal finding all (xi,yi)
combinations
that pass the fit criteria
Ingredients
• starting point (Start) found by (slightly) modified version
• step size (Δx, Δy)
• parameter boundaries
• fit procedure + acceptance tolerance fa (>1)
• three lists: rejected, accepted and unfinished
Limitation only for a connected region
D. Depla
1st EUCASS Aerospace Thematic Workshop
K. Strijckmans, W.P. Leroy, R. De Gryse, D. Depla
Surface and Coatings Technology 206 (2012) 3666-3675
www.DRAFT.ugent.be
27
14
Crash course
The processes
The model
The parameters
Examples
Conclusions
Fitting results : correlations
one-cell target
multi-cell target
D. Depla
Crash course
(fa = 1.5) experimental Yc
(fa = 3) ☺ experimental Yc
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
Examples
www.DRAFT.ugent.be
28
Conclusions
Fitting results : analysis
Reaction coefficient k and sputter yield oxide Yc
highly correlated
Power law Yc = b’ ka
ratio YAlc/YYc and correlation independent of
• reaction coefficient k
• one-cell or multi-cell target
• implantation profile
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
29
15
Crash course
The processes
The model
The parameters
Examples
Conclusions
Fitting : some remarks (1)
Using the experimental oxide sputter yields, we get a quite similar reaction rate for Y
and Al with implanted O atoms.
Restricting the possible reaction rate constants to the same values and within the
range of the experimental oxide sputter yields, we get a value for the sticking
coefficient on the target.
Al : 0.08±0.046
Y : 0.53 ±0.14
How this compares to literature ?
Aluminium : 0.0136 (average value over 6 different papers)
Yttrium : 0.44 (combination of 2 papers)
The fitted values are much higher : ion stimulated chemisorption, but mainly the
presence of atomic oxygen (sticking coefficient 1)
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
Examples
www.DRAFT.ugent.be
30
Conclusions
Fitting : some remarks (2)
Atomic flux to the molecular flux is order 0.1
So, not only the sputter yields fit, but also the sticking coefficients.
Al : 0.08±0.046
Y : 0.53 ±0.14
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
31
16
Crash course
The processes
The model
The parameters
Examples
Conclusions
The examples
The examples
Discharge voltage behaviour
Target rotation
Argon pressure influence
Critical point prediction
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
www.DRAFT.ugent.be
Examples
32
Conclusions
Discharge voltage behaviour
Flow
120 s
Duty cycle
between 100% and 0%
Target : Al (406.4x127 mm)
Reactive gas : O2
Constant current : 2 A
Argon flow : 50 sccm
Measurement performed at ENSAM (Cluny, France)
With cooperation of A. Besnard, N. Martin
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
33
17
Crash course
The processes
The model
The parameters
Examples
Conclusions
Details
Discharge voltage for a poisoned
target in Ar/O2
Small decrease when oxygen is
removed
Simple : effective ionisation
energy of Ar is lower as
compared to oxygen
D. Depla
Crash course
Discharge voltage for a metal
target in pure argon
Small increase on reactive gas
addition…
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
Examples
www.DRAFT.ugent.be
34
Conclusions
Details
We see this slight increase when
the oxygen pressure change is
small.
D. Depla
Simulation
:
the
coverage
by
chemisorption results in a voltage
increase, while compound formation
results in voltage decrease.
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
35
18
Crash course
The processes
The model
The parameters
Examples
Conclusions
Target rotation (1)
Hysteresis shifts to lower oxygen flow on increasing the rotation speed
D. Depla, J. Haemers, G. Buyle, R. De Gryse, J. Vac. Sci. Technol. Science A 24 (2006) 934
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
Examples
www.DRAFT.ugent.be
36
Conclusions
Target rotation (2)
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
37
19
Crash course
The processes
The model
The parameters
Examples
Conclusions
Target rotation : sputter cleaning (1)
Sputtering a stationary target, and then
sputter cleaning in pure argon while
rotating
X.Y. Li, D. Depla, W.P. Leroy, J. Haemers, R. De Gryse
J. Phys. D: Appl. Phys. 41 (2008) 035203 (6pp)
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
www.DRAFT.ugent.be
Examples
38
Conclusions
Target rotation : sputter cleaning (2)
More rounds
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
39
20
Crash course
The processes
The model
The parameters
Examples
Conclusions
Target rotation : sputter cleaning (3)
In poisoned mode : faster sputter cleaning than in metallic mode
Reason : the deposited layer is much thinner
because the deposition rate is much lower
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
Examples
www.DRAFT.ugent.be
40
Conclusions
Including deposition enables to mimick the sputter cleaning experiments
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
41
21
Crash course
The processes
The model
The parameters
Examples
Conclusions
tout
∆s
tin
• ∆S enters plasma region fully oxidized
• increase RPM → smaller tin = less time for oxide removal
• critical gas flow decreases with increasing RPM
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
Examples
www.DRAFT.ugent.be
42
Conclusions
Interpretation
Without deposition, we would expect a similar behaviour, i.e. 1/RPM behaviour
But with deposition
Lower rotation speed means a thicker layer,
but there is more time to sputter the layer
Higher rotation speed means a thinner layer,
but there is less time to sputter the layer
tout
∆s
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
43
22
Crash course
The processes
The model
The parameters
Examples
Conclusions
Argon pressure (1)
E. Särhammer, K. Strijckmans, T. Nyberg, S. Van Steenberge, S. Berg, D. Depla
Surface and Coatings Technology 232 (2013) 357
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
www.DRAFT.ugent.be
Examples
44
Conclusions
Argon pressure (2)
Low sticking coefficient
D. Depla
1st EUCASS Aerospace Thematic Workshop
High sticking coefficient
www.DRAFT.ugent.be
45
23
Crash course
The processes
The model
The parameters
Examples
Conclusions
Prediction of the first critical point
The first critical point is
defined as the lowest flow
before entering the poisoned
regime
Mainly defined by the reaction
of the reactive gas with the
deposited metal
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
www.DRAFT.ugent.be
Examples
46
Conclusions
Prediction and agreement
The RSD2013 model predicts not one… but two hysteresis curves.
Recently (paper just accepted in APL) this is now experimentally proven.
Origin :
1. The hysteresis originates from the
avalanche mechanism related to
the getter activity of the deposited
material.
2. Two conditions : the transition from
metallic mode to poisoned mode
results in avalanche mechanism
due to implanted, non-reactive
reactive ions.
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
51
24
Crash course
The processes
The model
The parameters
Examples
Conclusions
Conclusions
N. Mason
in “The plasma 2012 roadmap”
“Developing such models and
gaining
a
detailed
understanding of the physical
and chemical mechanisms
within plasma systems is
intricately linked to our
knowledge
of
the
key
interactions within the plasma
and thus the status of the
database for characterizing
electron, ion and photon
interactions with those atomic
and molecular species within
the plasma and knowledge of
both the cross-sections and
reaction rates for such
collisions, both in the gaseous
phase and on the surfaces of
the plasma reactor.”
The processes are relatively well
understood and described.
The model is (too) simple but
gives quantitative results, …
But the parameters are hard to get,
and needs dedicated experiments.
D. Depla
Crash course
1st EUCASS Aerospace Thematic Workshop
The processes
The model
The parameters
www.DRAFT.ugent.be
Examples
52
Conclusions
Acknowledgements
Further development of the RSD model
Simulations
Koen Strijckmans
Measurements of incorporation coefficients and sputter yields
Wouter Leroy
Further developments of the SiMTRA code
Francis Boydens
Oxide formation on the target
Roeland Schelfhout
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
53
25
Crash course
The processes
The model
The parameters
Examples
Conclusions
Learn more and enjoy …
December 1st and 2nd 2016
Downtown Ghent
www.rsd2016.be
Short course on Nov. 30th 2016
Invited speakers : H. Urbassek, R. Smith, E. Lewin, Z. Barber, and C. Schiffers
Sarton Chair Lecture by J. Greene
The
History
of
Ancient Metallurgy
Leading to Modern
Materials Science
D. Depla
1st EUCASS Aerospace Thematic Workshop
www.DRAFT.ugent.be
54
26