1

of Nb magnetron sputtered

thin films and dependence on sputtering parameters

Anna Skliarova, O. Azzolini, V. Palmieri

Porosity

2

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

3

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.

5

Our method of porosity evaluation

Al is providing fast reaction with

visible product revealing the pore sites

6

Our method of porosity evaluation

Sputtering of Al onto polished quartz allowed

minimizing the influence of the substrate defects

and focus on sputtering parameters

7

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

13

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

20

Investigated parameters:

• Magnetron position1

• Pressure2

• Temperature3

• Film thickness4

• Sample position 5

• DC-Biased MS6

21

Investigated parameters:

• Magnetron position1

• Pressure2

• Temperature3

• Film thickness4

• Sample position 5

• DC-Biased MS6

44

44

33

3

22

Temperature influence: acid test

Floating (~250°C)

400°C

500°C

0°C

-100°C

-50°C

300°C

Standard

44

44

33

3

23

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

27

Investigated parameters:

• Magnetron position1

• Pressure2

• Temperature3

• Film thickness4

• Sample position 5

• DC-Biased MS6

28

Investigated parameters:

• Magnetron position1

• Pressure2

• Temperature3

• Film thickness4

• Sample position 5

• DC-Biased MS6

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Influence of film thickness: acid test

43

22

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 :

35

1

ON AXIS

5

OUT OF AXIS

UBM II type: position influence

Acid test (1÷5)

36

1

ON AXIS

5

OUT OF AXIS

UBM II type: position influence

37

Investigated parameters:

• Magnetron position1

• Pressure2

• Temperature3

• Film thickness4

• Sample position 5

• DC-Biased MS6

38

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!

132

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Winners!

132

Biased MS

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Winners!

132

Biased MSHigh T MS

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Winners!

132

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:

47

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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