High resolution morphological and mechanical characterization of Niobium

High resolution morphological and mechanical characterization of Niobium films obtained by MS and Biased MS PVD n n E. Bemporad, M. Sebastiani, F. Carassiti University "Roma Tre", Dep't of Mechanical and Industrial Engineering Via Vasca Navale 79 - 00146 Rome Italy n e. bemporad@stm. uniroma 3. it The International Workshop on: Thin Films and new ideas for pushing the limits of RF superconductivity October 9 -12, 2006

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Roma Tre, some numbers… n n n www. uniroma 3. it 09/03/2021 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: u Civil u Computer Science u Electronic u Mechanical « Materials Science and Technology research group 3

Main objectives of presented work n n n 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 INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 4

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

Introduction n n Both structure and properties of films depend on deposition conditions used Increasing bias voltage increases the energy of bombardment ions, resulting in: u u u Densification of the film Increasing inherent compressive stress due to Ar incorporation Additional defects in coatings structure Changing in texture Preferential grow direction 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 n n Microstructural changes reflect also in mechanical properties changes By the measure of mechanical properties the effect of deposition condition on microstructure can be verified INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 7

Materials and Methods 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 INFN Workshop, 10 -2006 9 765 CERN type sputtering 12 766 CERN type sputtering YY 767 bias type sputtering (100 V) R 768 bias type sputtering (100 V) 4 769 CERN type sputtering 2 770 CERN type sputtering Q 771 bias type sputtering (100 V) LL 772 bias type sputtering (100 V) Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 9

Materials INFN Workshop, 10 -2006 9 765 CERN type sputtering 12 766 CERN type sputtering YY 767 bias type sputtering (100 V) R 768 bias type sputtering (100 V) 4 769 CERN type sputtering 2 770 CERN type sputtering Q 771 bias type sputtering (100 V) LL 772 bias type sputtering (100 V) Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 10

Methods n n OM and SEM observation, plan view and LN 2 cross-section Micro Hardness measurements, both Vickers and Knoop indenters, with loads ranging from 1 N down to 0, 005 N AFM in contact mode on the surface and inside indentation marks FIB-Cross. Beam cross-section on the surface and inside indentation marks (still ongoing) 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 n n n Elastic modulus obtained by 3 D 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; INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 12

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

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

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

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

Elastic modulus, Lesage model Model based on residual indent volume (VRe) measurement, and comparison with theoretical one. Indentation performed at low load (0, 005 N), so to have z < film thickness/10 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 J. Lesage et al. , Surface and Coating Technology 81 (1996) 269 -274 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, Marshall model D. B. Marshall, comunication of the American Ceramic Society, C-175 (1982) INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 19

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

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

ISE – Meyer, elasto-plastic behaviour σ σ σS σS ε High load, macro hardness INFN Workshop, 10 -2006 n ε Low or very low load, micro/nano hardness 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 Lower loads 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 Work hardening effect 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 Example: Ti 6 Al 4 V alloy INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 25

Hardness of coated systems HV Hardness of the film Plastic zone Models Film e High Load Plastic zone Load 1/d Substrate Low Hardness of the substrate

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

JÖNSSON & HOGMARK AF (1984) Geometrical representation x x AS Total area : B HF HS t 22° A Ductile material C=1 INFN Workshop, 10 -2006 B’ C HF t HS t C’ 11° A’ t Brittle material C=0. 5 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 28

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

Static and dynamic indentation n n 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 INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 30

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

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

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

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

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

Results deposition mode unbiased MS INFN Workshop, 10 -2006 ID Elastic modulus [GPa] HARDNESS MHV, [Kg/mm 2] # Lesage (ref. ) Jonsson. Hogmark Chicot. Lesage 4 -769 (103) 468, 3 (671, 9) 2 -770 (103) 508, 8 (685, 5) 9 -765 (103) 329, 3 (561, 5) 12 -766 54, 33 255, 3 337, 6 Q-771 (103) 547, 8 (617, 6) LL-772 (103) 542, 5 (716) YY-767 88, 95 478, 7 589, 1 R-768 (103) 663, 7 (794, 7) Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 36

Results n n 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, …). INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 37

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

Microstructure and morphology Ln 2 cross section, biased MS, #R-768 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 FIB cross section, unbiased MS, #2 -770 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 INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 41

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

Sub-micro morphology unbiased MS (#12 -766); grain size ≈ 300 nm biased MS (#R-768); grain size < 100 nm 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 unbiased MS (#12 -766); grain size ≈ 300 nm INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 44

Surface defects: FIB (25 k. V, 8. 000 x, SEM SE detector) INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 45

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

Sub-micro morphology biased MS (#R-768); grain size < 100 nm 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 G. Wu et al. / Thin Solid Films 489 (2005) 56– 62 51 V bias INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 48

Ion beam sputtering on deposited film n n n J. Appl. Phys. , Vol. 81, No. 10, Grain type A: 15 May 1997 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 Roughness is proportional to highly demote normalized energy and film growing thickness 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 biased MS (#Q-771) INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 50

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

Results THICKNESS # [µm] RMS Ra peak- to peak [nm] 4 -769 0, 73 8, 2 6, 5 55, 7 2 -770 0, 61 7, 1 5, 7 43 9 -765 1 (± 0, 1) 7, 6 6, 1 46 12 -766 1, 9 (± 0, 2) 8, 2 6, 6 43, 5 Q-771 1 12, 4 10 68 LL-772 0, 98 9, 4 7, 4 59, 3 YY-767 1, 3 11, 8 9, 7 62 R-768 0, 9 (± 0, 1) 12, 5 10, 2 68 deposition mode unbiased MS ROUGHNESS (7, 5 µm 2 investigated) ID 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 n n 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 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 n n n Unbiased MS films show a first growing thickness of about 200 nm 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 INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 54

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

Conclusion n Surface mechanical properties obtained form Vickers indentation of biased and unbiased MS Nb films has been correlated with microstructural 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 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 n n 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 INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 57

Further developments n n 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 INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 58

Thank you for your attention e. bemporad@stm. uniroma 3. it www. stm. uniroma 3. it INFN Workshop, 10 -2006 Bemporad et al. : High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD 59

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. uniroma 3. it