Post on 02-Jul-2015
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of Nb magnetron sputtered
thin films and dependence on sputtering parameters
Anna Skliarova, O. Azzolini, V. Palmieri
Porosity
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Pinholes in Nb film in SRF cavities
Resistance
to RF at
4.2K
RCu≈105RNb
Pinholes
expose
underlying
Cu
Cavity
surface
resistance
increase
Q-factor
EAcc
are lower
• To correlate Nb film porosity vs
sputtering parameters
• To find approaches to less porous Nb
films
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Aim of the research:
4S. Amorosi, C. Benvenuti, P. Chiggiato, M. Malabaila, Vacuum, V. 60, 1–2, 2001, 275-278
Method proposed by Amorosi et al.
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Our method of porosity evaluation
Al is providing fast reaction with
visible product revealing the pore sites
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Our method of porosity evaluation
Sputtering of Al onto polished quartz allowed
minimizing the influence of the substrate defects
and focus on sputtering parameters
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Our method of porosity evaluation
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1 2 3 4 5
Acid test evaluation: SCALE
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Standard conditions
- conditions to be considered standard if other
information is not provided below
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Standard conditions:
2” Planar UBM II type
STANDARD SAMPLE POSITION
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Standard conditions:
SAMPLE HOLDER
6 cm
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Standard conditions:
Ar as sputtering gas
Nb target RRR 300
Pbase ~10-6 mbar
IDC = 0.5 A
No heating/cooling substrate
Film thickness ~1.5 µm
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Investigated parameters:
• Magnetron position1
• Pressure2
• Temperature3
• Film thickness4
• Sample position 5
• DC-Biased MS6
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Investigated parameters:
• Magnetron position1
• Pressure2
• Temperature3
• Film thickness4
• Sample position 5
• DC-Biased MS6
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Magnetron position: acid test
MAGNETRON
MAGNETRON
SAMPLE HOLDER
Standard
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Investigated parameters:
• Magnetron position1
• Pressure2
• Temperature3
• Film thickness4
• Sample position 5
• DC-Biased MS6
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Investigated parameters:
• Magnetron position1
• Pressure2
• Temperature3
• Film thickness4
• Sample position 5
• DC-Biased MS6
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Pressure influence: acid porosity test
310-2
mbar310-3
mbar
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Pressure influence: acid porosity test
310-2
mbar310-3
mbar
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Investigated parameters:
• Magnetron position1
• Pressure2
• Temperature3
• Film thickness4
• Sample position 5
• DC-Biased MS6
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Investigated parameters:
• Magnetron position1
• Pressure2
• Temperature3
• Film thickness4
• Sample position 5
• DC-Biased MS6
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3
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Temperature influence: acid test
Floating (~250°C)
400°C
500°C
0°C
-100°C
-50°C
300°C
Standard
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3
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Temperature influence: acid test
Floating (~250°C)
400°C
500°C
0°C
-100°C
-50°C
300°C
Standard
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Optical profilometry
Scan area: 200 μm × 200 μm
Result: % of area covered by
holes deeper than 0.5 μm
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4 0.5 %
-100 °C
4 0.4 %
0 °C
4 1 %
Floating
3 0.04 %
500 °C
- 0 %
800 °C
Temperature influence: SEM
Acid test (1÷5)
Optical profilometry
(%)
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4 0.5 %
-100 °C
4 0.4 %
0 °C
4 1 %
Floating
3 0.04 %
500 °C
- 0 %
800 °C
Temperature influence: FIB SEM
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Investigated parameters:
• Magnetron position1
• Pressure2
• Temperature3
• Film thickness4
• Sample position 5
• DC-Biased MS6
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Investigated parameters:
• Magnetron position1
• Pressure2
• Temperature3
• Film thickness4
• Sample position 5
• DC-Biased MS6
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Influence of film thickness: acid test
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28 µm
6 µm
1.5 µm
4 µm
10 µmStandard
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Investigated parameters:
• Magnetron position1
• Pressure2
• Temperature3
• Film thickness4
• Sample position 5
• DC-Biased MS6
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Investigated parameters:
• Magnetron position1
• Pressure2
• Temperature3
• Film thickness4
• Sample position 5
• DC-Biased MS6
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UBM II type: sample position
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UBM II type: sample position
ON AXIS OUT OF AXIS
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UBM II type: sample position
ON AXIS OUT OF AXIS
1 5Acid porosity test :
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1
ON AXIS
5
OUT OF AXIS
UBM II type: position influence
Acid test (1÷5)
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1
ON AXIS
5
OUT OF AXIS
UBM II type: position influence
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Investigated parameters:
• Magnetron position1
• Pressure2
• Temperature3
• Film thickness4
• Sample position 5
• DC-Biased MS6
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Investigated parameters:
• Magnetron position1
• Pressure2
• Temperature3
• Film thickness4
• Sample position 5
• DC-Biased MS6
DC bias -80 V -50 V -80 V -80 V -150 V
Arpressure,
mbar310-2 510-3 510-2 310-3 310-3
Porosity acid test 3 2 1 1 2
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DC-biased MS
DC bias -80 V -50 V -80 V -80 V -150 V
Arpressure,
mbar310-2 510-3 510-2 310-3 310-3
Porosity acid test 3 2 1 1 2
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DC-biased MS
DC bias -80 V -50 V -80 V -80 V -150 V
Arpressure,
mbar310-2 510-3 510-2 310-3 310-3
Porosity acid test 3 2 1 1 2
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DC-biased MS
Amount of holes deeper 0.5 μm is 0.1 %
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DC-biased MS
SEM HR SEM
FIB SEM
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Winners!
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Winners!
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Biased MS
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Winners!
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Biased MSHigh T MS
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Winners!
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Biased MSHigh T MS
Thick film
• Increase film thickness1
• Substrate above magnetron2
• Proper substrate preparation3
• Avoiding UBM far out of axis4
• Clean room + vacuum cleaner5
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Methods to decrease porosity:
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Research team:
LNL INFN:
H.Skliarova, O. Azzolini, V. Palmieri
Hanna.Skliarova@lnl.infn.it
LIME Roma-Tre:
M. Renzelli, D. De Felicis, E. Bemporad