12th International Workshop on RF Superconductivity. A.Frigo, G.Lanza, H.Padamsee, V.Palmieri, D.Tonini

Transcription

1 12th International Workshop on RF Superconductivity A.Frigo, G.Lanza, H.Padamsee, V.Palmieri, D.Tonini

2 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)

3 Cylindrical Magnetron Magnet Cavity Niobium cathode

4 Q-slope problem Bulk Niobium Niobium sputtered film

5 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.

6 At different target-substrate angle relative intensity degrees 60 degrees 45 degrees 30 degrees 15 degrees Theta (degrees) AFM Roughness images XRD spectras Diploma thesis Morphology of Niobium Films Sputtered at Different Target-substrate Angles Diego Tonini, LNL-INFN, Material Science, Padova University.

7 At different target-substrate angle Increasing level of contamination Superconducting properties Diploma thesis Morphology of Niobium Films Sputtered at Different Target-substrate Angles Diego Tonini, LNL-INFN, Material Science, Padova University.

8 At different target-substrate angle Increasing level of contamination Electrical properties Diploma thesis Morphology of Niobium Films Sputtered at Different Target-substrate Angles Diego Tonini, LNL-INFN, Material Science, Padova University.

9 Comparing Sputtering and Cathodic Arc Sputtered films grow along the normal to 110 crystal planes according to the atom arrival direction By cathodic arc, the substrate is biased; so ions always reach the substrate perpendicularly: NO TEXTURE vs target-substrate angle G. Keppel, V. Palmieri, N. Patron, D. Tonini, LNL-INFN

10 Understanding: Film morphology strictly correlated to the deposition angle Electrical and superconducting film properties degrade vs deposition angle Comprehension of sputtering principles is compulsory for conceiving new magnetron configurations

11 Deposition technique: magnetron sputtering B V e - V e // Uniform magnetic field lines ω c B

12 Deposition technique: magnetron sputtering E - Target ω m Non-uniform Magnetic field lines - Electron reflection is due to magnetostatic and electrostatic mirror

13 Deposition technique: magnetron sputtering Cylindrical Post Magnetron cathode E B B ω D 2 - B

14 Deposition technique: magnetron sputtering If E B - Cylindrical Post Magnetron cathode Higher ionisation efficiency B

15 Ideas to improve the film quality: 1. Increasing the sputtering rate R f i = N i N α i α i i + R ƒ i = Fraction of impurities trapped into the film α i = Impurities sticking coefficient N i = Number of atoms impurities arriving on the film surface

16 Target shape Plasma Target B 2 inches planar target

17 Target shape Plasma Target B 2 inches squared target

18 Target shape Plasma Target B 2 inches rounded target

19 Cathode shape modification 3,5 p = 2,5 * 10-2 mbar Fit: I = a*v b 3,0 2,5 Rounded target b = 9,0 Squared target b = 8,3 Increasing sputtering rate Current (A) 2,0 1,5 1,0 Planar target b = 6,9 0, Cathode potential (v)

20 Ideas to improve the film quality: 1. Increasing the sputtering rate R 2. Reducing the deposition angle

21 Cathode shape modification Cathode B E B // cathode surface Cavity B Magnet Higher deposition rate

22 Cathode shape modification Niobium ring positioned in the cell center

23 Cathode shape modification

24 Ideas to improve the film quality: 1. Increasing the sputtering rate R 2. Reducing the deposition angle 3. Promoting atoms rearrangement and impurities re-sputtering during film growing ( N ) iαi β fi = N α β + ( ) R i i ƒ i = fraction of impurities trapped into the film α i = impurities sticking coefficient N i = atoms impurities arriving on the film β = function of the bias current due to impurities ions R = sputtering rate

25 Biased Diode Sputtering Bias LNL Up to now The bias technique is highly reliable: over 40 QWRs are installed and working at LNL

26 Biased Magnetron Sputtering Magnet Cathode V Biased Grid +200 V Grounded Cavity

27 Biased Magnetron Sputtering Biased grid

28 Biased Magnetron Sputtering

29 Biased Magnetron Sputtering

30 Biased Magnetron Sputtering

31 Biased Magnetron Sputtering

32 Biased Magnetron Sputtering

33 Biased Magnetron Sputtering

34 Biased Magnetron Sputtering

35 Ideas to improve the film quality: 1. Increasing the sputtering rate R 2. Reducing the deposition angle 3. Promoting atoms rearrangement and impurities re-sputtering during film growing 4. Increase the cathode/substrate area ratio

36 Biased Diode Sputtering Bias CERN Low ratio cathode/substrate area Low sputtering rate (1 micron /day)

37 Cavity shaped cathode High ratio cathode/substrate area

38 Cavity shaped cathode in progress

39 Conclusion Three new magnetron sputtering configurations are ready!...soon 20 cavities to measure.

40

41 Cylindrical Post-Magnetron Magnetic field lines follow the cavity shape Cavity B Niobium cathode