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Development of thin films for
superconducting RF cavities in ASTeC
O.B. Malyshev and R. Valizadeh
on behalf of collaboration team
ASTeC Vacuum Science Group,
STFC Daresbury Laboratory, UK
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 2
• Motivation
• PVD deposition
• CVD/ALD deposition
• Surface analysis
• Superconductivity evaluation
• RF sample test
• Future plans
• Conclusions
Outlook
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 3
Motivation
• The aim is to develop the PVD and CVD coating
technologies of superconducting materials (including high
temperature ones) for RF cavities and apply it on the RF
cavities
• Objectives:
• a systematic study correlation between
• Deposition condition
• Film morphology, structure, chemistry
• AC and DC superconductivity characteristics such as Tc, Bc,
RRR, etc.
• RF evaluation of samples
• Cavity deposition and test
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 4
UHV PVD facility• Bakeable
• Load-lock chamber
• 100 mm diam.
• Three planar
concentric targets
with the variable
distance to the
substrate: 10-15 cm
• Substrate rotation
• Ion beam assist
• 20 Ts 950 ºC
• Differential RGA
pumping to analyse
the sputter gas.
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 5
• Base pressure = 10-9 mbar
• Kr pressure during sputtering
• P = 10-3 mbar
• Power at magnetron:100-600 W
• DC sputtering
• Pulsed DC sputtering 100-350 kHz
with an off time of 1.1 µs.
• HiPIMS
PVD deposition
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0
50
100
150
200
250
300
350
400
450
500
100 200 300 400 500 600
Cu
rren
t (A
)
Vo
ltag
e (V
)
Power (W)
Voltage
Current
• On a substrate:
• DC and RF Bias on a substrate:
• A bias voltage to the substrate was varied 0 - 150 V.
• Ion beam assisted
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 6
Sample insertion system
- MgO, Si and Cu substrates deposited together.
- Different substrates can be compared when
deposited with same plasma in same conditions.
Up to 6 samples load
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 7
• Base pressure:
• 1.5 x 10-5 mbar at 120 ºC
• Gas flows:
• Argon, Max 5 l/min, 200
sccm MFC
• Hydrogen, Max 1 l/min, 100
sccm MFC
• Heater tested up to 500 ºC
(could go 950 ºC)
PECVD/ALD deposition
• First Nb film using NbCl5 precursor was deposited
on last Friday
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 8
ALD rig
ALD valves:
tested with
Arduino control,
switching <1 ms
Plasma
waveguide
Reactor
chamber
Sample holder
SAES gas purifiers
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 9
• XRD analysis
• average grain size and lattice orientations within the film.
• XPS analysis
• film composition and impurity
• EBSD analysis
• an accurate value for the grain size at the surface of the
film.
• SEM analysis
• to determine the film thickness and growth rates.
• to give an indication of the type of film that has been
deposited i.e., columnar with voids or densely packed
grains.
Film Morphology
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 10
Multi-Probe UHV XPS, AES, AFM, STM, LEED and ISS
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 11
• Nb grain sizes within our films:
• 9±2 nm for P < 400 W
• 18±3 nm for 400 W < P < 600 W.
• This is similar in size to the
grains produced in other studies.
• A peak 2θ intensity:
• Most films at ~40⁰ which corresponds to the (220) lattice orientation.
• Only 3 samples: at 71⁰ (321).
• RRR values show no preferred orientation between the two values
of 2θ as the highest RRR values were recorded for both.
Film Morphology: XRD
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 12
XPS analysis
C 1s
O 1s
Nb 3d5/2
Nb 3d3/2
Nb 3p3/2
Nb 3p1/2
Nb 3s
As received
Ar+ bombarded
x 102
10
20
30
40
50
60
70
80C
PS
600 500 400 300 200 100 0
Binding Energy (eV)
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 13
Nb: 3d3/2 (205) and 3d5/2 (202)
As receivedAr+ bombarded
Nb
3d
Nb
3d
x 102
0
10
20
30
40
50
60
70
CP
S
214 212 210 208 206 204 202 200 198 196
Binding Energy (eV)
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 14
O 1s (531)
O 1
sO
1s
x 102
0
5
10
15
20
25
30
35
40
CP
S
540 538 536 534 532 530 528 526
Binding Energy (eV)
As receivedAr+ bombarded
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 15
C 1s
C 1
s
C 1
s
x 102
0
2
4
6
8
10
12
14
CP
S
294 292 290 288 286 284 282 280 278
Binding Energy (eV)
As receivedAr+ bombarded
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 16
samples deposited
with a 50-V bias
Film Morphology: SEMsamples deposited without a bias
02468
101214161820
100 300 500
Gro
wth
Rat
e (
nm
/min
)
Power (W)
0 V
50 V
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 17
• Only one sample has been analysed using EBSD
• EBSD data shows grains larger than 18 nm present in the
sample, the largest of which are of the order 250 nm across
their longest axis. The larger grains are surrounded by a
matrix of smaller grains of a similar size to those described by
XRD.
Film Morphology: EBSD
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 18
• RRR measurements
• have been performed using a purpose built cryostat
housing a four point probe.
• DC SQUID measurements
• were performed using a Quantum Design PPMS. The
measurement gives values for both the first and second
critical fields, Hc1 and Hc2.
Superconductivity evaluation
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 19
• In all cases
• RRR is higher for a
biased substrate than
with unbiased
• However, increasing
the bias further does
not always result with
increasing RRR
Superconductivity evaluation: RRR
• 2 RRR 22 for 70 samples studied.
• Samples with RRR ≥ 10 were deposited with
300 ≤ P ≤ 600 W.
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 20
Hc1
Hc1
Hc1
Hc2
Hc1
Hc1
Hc2
Hc2
Hc2
Hc2
Hsmp Hsmp
Hsmp Hsmp
Hsmp
Superconductivity evaluation: DC SQUID
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 21
• 5 samples studied for B perpendicular to the sample surface
• 2 samples studied for B parallel to the sample surface
Superconductivity evaluation: DC SQUID
A typical DC magnetic susceptibility
measurement with the sample parallel to the
magnetic field.
Some results are quite
unexpectable
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 22
HC2 increases with RRR at T = 6 K
RRR vs Hc2
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 23
What we are looking for?
We have to find a criteria for
a simple evaluation of
deposited film to predict its
behaviour in RF field
• To stay in Meissner state would
be ideal (Q0 conditions)
• T<T1
• Should the criteria for a good
film be Hsmp?
• Is it valid for RF?
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 24
We would like to make a
simple RF evaluation of
deposited film
• Tangential magnetic field
• Surface resistance
(power loss)
measurements at each
part
• Nb coated sample
comparison to bulk Nb
and other samples
RF sample test: idea
Nb plate
Nbcylinder
Nb coated Cu plate
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 25
RF modelling for 3.9 GHz
H-field
E-field• The idea was found to be
working
• There is an RF leakage
in the gaps
• Optimisation work
on bandwidth and
behaviour at very
high conductivity
with Microwave
Studio
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 26
• Mock up 3.9 GHz pill
box cavity has been
fabricated to validate
the simulation results
obtained with
Microwave Studio.
• An order for a niobium
7.8 GHz cavity is in
place.
• Samples:
• a 100-mm diam. Nb disk
• a 100-mm diam. copper
disk with thin films of Nb
deposited on the
surface.
Aluminium mock up RF cavity test
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 27
• HiPIMS sample deposition
• Nb, NbN, NbCN, Nb3Ge MgB2
• Plasma ALD deposition
• Nb, NbN, NbCN, MgB2
• RRR measurements
• AC and DC magnetisation measurements
• RF pill-box test facility
• Building up a test facility (Dec 2014)
• Testing with a bulk Nb disk (Jan 2015)
• Sample measurements (beginning 2015)
• 3D coating
Future plans
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 28
New surface analysis rigs: SIMS
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 29
New surface analysis rigs: Auger microscope
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 30
• Lakeshore 7000
AC Susceptometer
• Complex susceptibility
’ and ”
• Differential
susceptibility
• Frequency effect
• AC amplitude effect
• Temperature effect
• Sensitivity 210-7 Oe
Superconductivity evaluation:
New AC susceptibility
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 31
• Quality of the film (morphology, RRR, Hc2)
depends on
• deposition parameters such as
• Substrate temperature,
• Ion/atom arrival ratio,
• Substrate bias,
• Plasma generation at the target
• pulsed or not
• HiPIMS
• Substrate crystallography
Conclusions
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 32
• Sample evaluation
• RF pill-box cavity is the best
• Cost of manufacturing and cost of LHe,
• Time consuming
• AC and DC susceptibility:
• Not direct for RF (Hc1 and Hc2) and a cost of LHe
• Quicker
• TC and RRR is an initial of evaluation
• RRR > 10-15, but quite indirect
• Quick, cheap
• Surface analysis (to explain what’s gone wrong):
• Dense or columnar
• Grain size
• Composition and impurity
• Defect’s density
Conclusions (2)
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 33
Dr. R. Valizadeh, Dr. O.B. Malyshev,A. Hannah, D.O. Malyshev, S. Pattalwar, J. HerbertA. Wheelhouse, P. McIntosh
Dr. G. Stenning
The UK’s SRF collaboration team
S. Wilde, Dr. B. Chesca
P. Pizzol, Prof. P. ChalkerF. Lockwood-Estrin, Prof. J. Bradley
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 34
ESCAlab-II: monochromated XPS,
mapping Auger, UPS
O.B. MalyshevThin films and new ideas for SRF,
6-8 October 2014, Legnaro, Italy 35
• If the desired material is not a binary compound but a single element one, such
as metals or semiconductors, it is very difficult to obtain them using the standard
ALD process. This is one of the reasons why Plasma enhanced ALD was
invented (PEALD).
• Through the use of a plasma source it is possible to generate hydrogen radicals
necessary to reduce the metal or semiconductor precursor. There are different
types of PEALD according to where the plasma source is positioned: if the
radicals are generated away from the reaction chamber and injected like any
other precursor the technique is called Radical enhanced ALD (Figure (a)).
Direct plasma ALD (Figure (b)) is when the plasma develops very close to the
substrate, while Remote plasma ALD (Figure (c)) is when the plasma is tens of
centimeters away from the substrate.
Plasma enhanced atomic layer deposition (PEALD)