a.frigo, g.lanza, h.padamsee, v.palmieri, d.tonini · cylindricalpost-magnetron niobium cathode...

A.Frigo, G.Lanza, H.Padamsee, V.Palmieri, D.Tonini

12th International Workshop on RF Superconductivity

CERN geometry

C. Benvenuti, S. Calatroni, I.E. Campisi, P. Darriulat, M.A. Peck, R. Russo, A.-M. Valente, “Study of the surface resistance of superconducting niobium films at 1.5 GHz”, Physica C 316 (1999) 153-188.

Cylindrical Magnetron

Niobiumcathode

Cavity

Magnet

Q-slope problem

Bulk Niobium

Niobium sputtered film

The INFN-LNL hypothesis

Sputtering at different target-substrate angle

Diploma thesis “Morphology of Niobium Films Sputtered at Different Target-substrate Angles” Diego Tonini, LNL-INFN, Material Science, Padova University.

20 40 60 80 100 120 1400

20

40

60

80

100

3 2 12 2 23 1 0 2 2 0

2 1 12 0 0

1 1 0

75 degrees

60 degrees

45 degrees

30 degrees

15 degreesre

lativ

e in

tens

ity

2 Theta (degrees)

AFM Roughness images XRD spectras

At different target-substrate angle

Diploma thesis “Morphology of Niobium Films Sputtered at Different Target-substrate Angles” Diego Tonini, LNL-INFN, Material Science, Padova University.

At different target-substrate angle

Superconducting propertiesDiploma thesis “Morphology of Niobium Films Sputtered at Different Target-substrate Angles” Diego Tonini, LNL-INFN, Material Science, Padova University.

Increasing level of contamination

At different target-substrate angle

Electrical propertiesDiploma thesis “Morphology of Niobium Films Sputtered at Different Target-substrate Angles” Diego Tonini, LNL-INFN, Material Science, Padova University.

Increasing level of contamination

Comparing Sputtering and Cathodic ArcSputtered films grow along the normal to 110 crystal planesaccording to the atom arrival direction

By cathodic arc, the substrate is biased; so ions always reach the substrateperpendicularly: NO TEXTURE vs target-substrate angle

G. Keppel, V. Palmieri, N. Patron, D. Tonini, LNL-INFN

Understanding:

• Film morphology strictly correlated to the deposition angle

• Electrical and superconducting film properties degrade vsdeposition angle

• Comprehension of sputtering principles is compulsory forconceiving new magnetron configurations

-

Uniformmagneticfield lines

Ve //

Deposition technique: magnetron sputtering

Ve ┴

B

Bc ∝ω

Non-uniformMagnetic field

lines

Deposition technique: magnetron sputtering

• Electron reflection is due to magnetostatic and electrostaticmirror

- -

E

mωTarget

B

Deposition technique: magnetron sputtering

2BBE

D×

∝ω-

Cylindrical Post Magnetron

cathode

-

B

Cylindrical Post Magnetron

cathode

Deposition technique: magnetron sputtering

If

E ┴ B

Higherionisationefficiency

1. Increasing the sputtering rate R

Ideas to improve the film quality:

αα

=+

i ii

i i

NfN R

αi = Impurities sticking coefficient

ƒi = Fraction of impurities trapped into the film

Ni = Number of atoms impurities arriving on the film surface

Target shape

B

Target

Plasma

2 inches planar target

Target shape

Target

Plasma

2 inches squared target

B

Target shape

Target

Plasma

2 inches rounded target

B

200 220 240 260 280 300 3200,5

1,0

1,5

2,0

2,5

3,0

3,5

Planar target b = 6,9

Squared targetb = 8,3

p = 2,5 * 10-2 mbar

Fit: I = a*Vb

Cur

rent

(A)

Cathode potential (v)

Rounded targetb = 9,0

Increasingsputtering

rate

Cathode shape modification

1. Increasing the sputtering rate R

2. Reducing the deposition angle

Ideas to improve the film quality:

Cathode shape modification

Cathode

Cavity

B

• B ┴ E

• B // cathode surface

Higherdeposition rate

Magnet

Niobium ring positioned in the cell center

Cathode shape modification

Cathode shape modification

1. Increasing the sputtering rate R2. Reducing the deposition angle3. Promoting atoms rearrangement and

impurities re-sputtering during film growing

Ideas to improve the film quality:

( )( ) RN

Nfii

iii +−

−=

βαβα

ƒi = fraction of impurities trapped into the film

αi = impurities sticking coefficientNi = atoms impurities arriving on the film β = function of the bias current due to

impurities ionsR = sputtering rate

Biased Diode Sputtering

The bias technique is highly reliable: over 40 QWRs are installed and working at LNL

Bias LNL Up to now

GroundedCavity

MagnetCathode- 250 V

BiasedGrid+200 V

Biased Magnetron Sputtering

Biased grid

Biased Magnetron Sputtering

Biased Magnetron Sputtering

Biased Magnetron Sputtering

Biased Magnetron Sputtering

Biased Magnetron Sputtering

Biased Magnetron Sputtering

Biased Magnetron Sputtering

Biased Magnetron Sputtering

1. Increasing the sputtering rate R2. Reducing the deposition angle3. Promoting atoms rearrangement and

impurities re-sputtering during film growing

4. Increase the cathode/substrate area ratio

Ideas to improve the film quality:

Biased Diode Sputtering

Bias CERN

Low ratio cathode/substrate

area

Low sputtering rate (1 micron /day)

Cavity shaped cathode

High ratio cathode/substrate

area

Cavity shaped cathode

in progress…

Cavity shaped cathode

Conclusion

Three new magnetron sputtering configurations are ready!

...soon 2 cavities to measure.0

Cylindrical Post-Magnetron

Niobiumcathode

Cavity

B

Magnetic field lines followthe cavity shape