A.Frigo, G.Lanza, H.Padamsee, V.Palmieri, D.Tonini · CylindricalPost-Magnetron Niobium cathode...
Transcript of A.Frigo, G.Lanza, H.Padamsee, V.Palmieri, D.Tonini · CylindricalPost-Magnetron Niobium cathode...
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A.Frigo, G.Lanza, H.Padamsee, V.Palmieri, D.Tonini
12th International Workshop on RF Superconductivity
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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.
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Cylindrical Magnetron
Niobiumcathode
Cavity
Magnet
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Q-slope problem
Bulk Niobium
Niobium sputtered film
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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.
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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.
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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
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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
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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
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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
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-
Uniformmagneticfield lines
Ve //
Deposition technique: magnetron sputtering
Ve ┴
B
Bc ∝ω
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Non-uniformMagnetic field
lines
Deposition technique: magnetron sputtering
• Electron reflection is due to magnetostatic and electrostaticmirror
- -
E
mωTarget
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B
Deposition technique: magnetron sputtering
2BBE
D×
∝ω-
Cylindrical Post Magnetron
cathode
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-
B
Cylindrical Post Magnetron
cathode
Deposition technique: magnetron sputtering
If
E ┴ B
Higherionisationefficiency
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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
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Target shape
B
Target
Plasma
2 inches planar target
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Target shape
Target
Plasma
2 inches squared target
B
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Target shape
Target
Plasma
2 inches rounded target
B
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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
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1. Increasing the sputtering rate R
2. Reducing the deposition angle
Ideas to improve the film quality:
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Cathode shape modification
Cathode
Cavity
B
• B ┴ E
• B // cathode surface
Higherdeposition rate
Magnet
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Niobium ring positioned in the cell center
Cathode shape modification
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Cathode shape modification
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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
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Biased Diode Sputtering
The bias technique is highly reliable: over 40 QWRs are installed and working at LNL
Bias LNL Up to now
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GroundedCavity
MagnetCathode- 250 V
BiasedGrid+200 V
Biased Magnetron Sputtering
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Biased grid
Biased Magnetron Sputtering
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Biased Magnetron Sputtering
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Biased Magnetron Sputtering
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Biased Magnetron Sputtering
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Biased Magnetron Sputtering
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Biased Magnetron Sputtering
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Biased Magnetron Sputtering
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Biased Magnetron Sputtering
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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:
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Biased Diode Sputtering
Bias CERN
Low ratio cathode/substrate
area
Low sputtering rate (1 micron /day)
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Cavity shaped cathode
High ratio cathode/substrate
area
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Cavity shaped cathode
in progress…
Cavity shaped cathode
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Conclusion
Three new magnetron sputtering configurations are ready!
...soon 2 cavities to measure.0
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Cylindrical Post-Magnetron
Niobiumcathode
Cavity
B
Magnetic field lines followthe cavity shape