1. High resolution morphological and mechanical characterization of Niobium films obtained by MS and Biased MS PVD E. Bemporad, M. Sebastiani, F. Carassiti University "Roma Tre", Dep't of Mechanical and Industrial Engineering Via Vasca Navale 79 - 00146 Rome Italy e.bemporad@stm.uniroma3.it The International Workshop on: Thin Films and new ideas for pushing the limits of RF superconductivity October 9-12, 2006

2. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 2 Where is the University “Roma Tre”? Rome

3. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 3 Roma Tre, some numbers… Born in 1992. One of the 4 State University in Rome (9 in total). 125.000 m 2. More than 40.000 students (3.900 enrolled in Engineering) More than 700 Researchers and Professors. Faculty of Engineering:  Civil  Computer Science  Electronic  Mechanical  Materials Science and Technology research group www.uniroma3.it

4. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 4 Main objectives of presented work To measure basic surface mechanical properties of Nb films, such as hardness, Elastic modulus and work hardening behaviour; To correlate this data with microstructure and surface roughness, which greatly affect the transition temperature (Tc) and the Residual Resistivity Ratio (RRR) of Nb films. To compare results obtained from biased MS and non biased MS films

5. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 5 Outline Introduction Materials and methods  Modelling of basic surface mechanical properties overview Results  Mechanical properties  Microstructure and morphology Discussion and conclusions Further developments

6. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 6 Introduction Both structure and properties of films depend on deposition conditions used Increasing bias voltage increases the energy of bombardment ions, resulting in:  Densification of the film  Increasing inherent compressive stress due to Ar incorporation  Additional defects in coatings structure  Changing in texture  Preferential grow direction

7. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 7 Introduction Microstructural changes reflect also in mechanical properties changes By the measure of mechanical properties the effect of deposition condition on microstructure can be verified

8. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 8 Materials and Methods

9. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 9 Materials 9765CERN type sputtering 12766CERN type sputtering YY767bias type sputtering (100V) R768bias type sputtering (100V) 4769CERN type sputtering 2770CERN type sputtering Q771bias type sputtering (100V) LL772bias type sputtering (100V)

10. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 10 Materials 9765CERN type sputtering 12766CERN type sputtering YY767bias type sputtering (100V) R768bias type sputtering (100V) 4769CERN type sputtering 2770CERN type sputtering Q771bias type sputtering (100V) LL772bias type sputtering (100V)

11. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 11 Methods OM and SEM observation, plan view and LN 2 cross-section Micro Hardness measurements, both Vickers and Knoop indenters, with loads ranging from 1N down to 0,005N AFM in contact mode on the surface and inside indentation marks FIB-CrossBeam cross-section on the surface and inside indentation marks (still ongoing)

12. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 12 Methods Elastic modulus obtained by 3D reconstruction of residual indent volume and applying Lesage (on Vickers indent) and Marshall (on Knoop indents) models. Work hardening behavior evaluated by the Indentation Size Effect (Meyer model); Intrinsic hardness obtained applying Jonsson-Hogmark and Chicot-Lesage hardness models;

13. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 13 Modeling of basic surface mechanical properties

14. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 14 Vickers indenter

15. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 15 Knoop indenter

16. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 16 Vickers indentation at different loads

17. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 17 Elastic modulus, Lesage model Indentation performed at low load (0,005N), so to have z < film thickness/10 Model based on residual indent volume (V Re ) measurement, and comparison with the theoretical one.

18. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 18 Elastic modulus, Lesage model J.Lesage et al., Surface and Coating Technology 81 (1996) 269-274

19. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 19 Elastic modulus, Marshall model D.B.Marshall, comunication of the American Ceramic Society, C-175 (1982)

20. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 20 Vickers hardness

21. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 21 Knoop hardness φ θ L = 7,114w

22. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 22 ISE – Meyer, elasto-plastic behaviour σ σSσS ε ε σSσS σ n High load, macro hardness Low or very low load, micro/nano hardness

23. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 23 ISE – Meyer, elasto-plastic behaviour Lower loads

24. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 24 ISE – Meyer, elasto-plastic behaviour Lower loads Work hardening effect

25. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 25 ISE – Meyer, elasto-plastic behaviour Example: Ti6Al4V alloy

26. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 26 Hardness of coated systems Hardness of the substrate Hardness of the film 1/d HV Models Plastic zone High Load Substrate Film Low Load Substrate Film

27. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 27 Hardness of coated systems

28. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 28 x x t t HSHS HFHF A B C 22° t t HSHS HFHF A’ B’ C’ 11° Ductile material Brittle material Geometrical representation AFAF ASAS Total area : C=1 C=0.5 JÖNSSON & HOGMARK(1984)

29. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 29 + Chicot & Lesage(1995)

30. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 30 Static and dynamic indentation All model presented are based on measurements performed on the residual indent. Some equipments, called depth sensing indenter, let to measure the load displacement curve during the indentation test In this case the Oliver and Pharr method gives a way to evaluate hardness and Elastic modulus simultaneously, for a given maximum load No data on depth sensing indentation will be reported in this work

31. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 31 Results

32. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 32 MHV at 0,5 g load

33. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 33 Elastic modulus and ISE Biased MS E = 88,95 GPa unbiased MS E = 54,33 GPa

34. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 34 Hardness comparison biased MS (#YY-767) unbiased MS (#12-766)

35. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 35 Hardness comparison

36. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 36 Results ID Elastic modulus [GPa] HARDNESS MHV, [Kg/mm 2 ] deposition mode # Lesage (ref.) Jonsson- Hogmark Chicot- Lesage unbiased MS 4-769(103)468,3(671,9) 2-770(103)508,8(685,5) 9-765(103)329,3(561,5) 12-76654,33255,3337,6 biased MS Q-771(103)547,8(617,6) LL-772(103)542,5(716) YY-76788,95478,7589,1 R-768(103)663,7(794,7)

37. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 37 Results Biased MS films show more than 50% higher MHV hardness then unbiased MS films Biased films are more prone to be work hardened with respect to unbiased films Elastic modulus of biased MS films resulted to be more than 60% higher than unbiased MS films Such differences in Elastic Modulus are obviously not due to changes in the Nb Elastic properties, but due to a variation of coating microstructure (density, homogeneity, grain growth direction,…).

38. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 38 Micro morphology biased MS unbiased MS Cu substrate

39. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 39 Microstructure and morphology Ln 2 cross section, biased MS, #R-768

40. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 40 Microstructure and morphology FIB cross section, unbiased MS, #2-770

41. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 41 Microstructure and morphology FIB cross section, unbiased MS, #2-770

42. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 42 Results Halbritter, Journal Of Applied Physics 97, 083904 (April, 2005)

43. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 43 Sub-micro morphology biased MS (#R-768); grain size < 100nm unbiased MS (#12-766); grain size ≈ 300nm

44. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 44 Sub-micro morphology unbiased MS (#12-766); grain size ≈ 300nm

45. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 45 Surface defects: FIB (25 kV, 8.000 x, SEM SE detector)

46. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 46 Microdroplets

47. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 47 Sub-micro morphology biased MS (#R-768); grain size < 100nm

48. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 48 Sub-micro morphology G. Wu et al. / Thin Solid Films 489 (2005) 56– 62 51V bias

49. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 49 Ion beam sputtering on deposited film Grain type A: channeling direction aligned with ion beam promote growing Grain type B: shadowed by type A grain growing, demote growing Grain type C: high ion sputter rate highly demote growing J. Appl. Phys., Vol. 81, No. 10, 15 May 1997 Roughness is proportional to normalized energy and film thickness

50. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 50 Ion beam sputtering on deposited film biased MS (#Q-771)

51. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 51 Roughness

52. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 52 Results IDTHICKNESS ROUGHNESS (7,5 µm 2 investigated) deposition mode #[µm]RMSRaRa peak- to peak [nm] unbiased MS 4-7690,738,26,555,7 2-7700,617,15,743 9-7651 (±0,1)7,66,146 12-7661,9 (±0,2)8,26,643,5 biased MS Q-771112,41068 LL-7720,989,47,459,3 YY-7671,311,89,762 R-7680,9 (±0,1)12,510,268

53. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 53 Results At a macroscopic scale, biased films seem to replicate substrate morphology, whilst unbiased films seem to flatten substrate surface At sub-micrometric scale, biased films showed an higher roughness that the unbiased films

54. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 54 Results Unbiased MS films show a first growing thickness of about 200nm with a polycrystalline shape, afterward grains are all columnar Columnar grains bend without apparent cracks, so showing a low value of residual stress compared to Nb strength Grains dimension is lower for biased films, with an apparent influence on grain growth direction

55. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 55 Conclusions

56. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 56 Conclusion Surface mechanical properties obtained form Vickers indentation of biased and unbiased MS Nb films has been correlated with micro- structural and morphological properties Results confirmed that biased MS films shows higher hardness, higher Elastic modulus, higher work hardening behavior, coupled with higher roughness compared with unbiased films Preferential sputtering of biased MS films based on crystallographic orientation are also observed, driving to the growth of elongated grains

57. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 57 Conclusion After hardness measurement and the use of models to extrapolate true film hardness, some useful information on density and residual stress can be estimated by the evaluation of the work hardening attitude and the elastic modulus calculation. The combined use of FIB and AFM techniques confirmed to be the best choice for the evaluation of microstructural and morphological parameters

58. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 58 Further developments More statistics Applying Marshall model to evaluate Elastic modulus via in-plane recovery of Knoop indent Complete FIB characterization of oxide layer thickness, grain size and growth defects for both type of films Use of Finite Element Modeling to foresee behavior of multilayer “soft on soft” films

59. INFN Workshop, 10-2006 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 59 Thank you for your attention e.bemporad@stm.uniroma3.it www.stm.uniroma3.it

60. DIMI - STM Material Science and Technology Research Group Structural and thermo-mechanical applications Università di Roma - Roma TRE Via Vasca Navale, 79 00146 – Roma WEB SITE: http://www.lime.uniroma3.it