R ESIDUAL STRESS MEASUREMENT BY FIB A controlled removal of a small - PowerPoint PPT Presentation

F OCUSED I ON B EAM TECHNIQUES FOR RESIDUAL STRESS ANALYSIS AT THE MICRON - SCALE Marco Sebastiani University of Rome «Roma TRE» Engi nee ri ng Department Materials Science and Technology Group 7th Annual FIB SEM Workshop Thursday, February 27th, 2014 Kossiakoff Center Johns Hopkins Applied Physics Laboratory Laurel, MD

Marco Sebastiani R ESIDUAL STRESS ANALYSIS ON A MICRON - SCALE Intra-grain stress analysis in polycristalline alloys and TBCs FIB user group 2014 Thin coatings and MEMS 2

Marco Sebastiani G AP OF KNOWLEDGE  Research needs Many advanced materials and devices require  stress measurement with sub-micrometer 3D spatial resolution Existing high resolution methods (i.e. using  synchrotron XRD, EBSD) are very expensive, time consuming and not suitable for amorphous materials  Production needs New developed procedures should also be  dow ngradable to in-line quality control processes, or at least cost-saving with respect to FIB user group 2014 traditional high resolution characterisation techniques. Innovative HR resolution should be standardised.  3

Marco Sebastiani R ESIDUAL STRESS MEASUREMENT BY FIB  A controlled removal of a small material volume is performed by FI B at low ion current (10-100 pA);  The attendant relaxation strain is then measured, step-by-step, by Digital I m age Correlation ( DI C) techniques;  The residual stress (in –plane distribution and depth profile) is then calculated from the measured strain by using either analytical or Finite Elem ent m odelling FIB user group 2014 4

Marco Sebastiani I MPLEMENTATI ON OF FI B- DI C PROCEDURES Focused I on • Geometries Beam controlled • Surface patterning material removal, • FIB milling parameters by the ring-core • SEM imaging parameters milling geometry • 2D strain mapping; Digital I m age Correlation for • Control of SEM noise strain • Best patterning for DIC measurement • GUI • FEM of influence functions for several geometries Residual stress • Models to correct for Elastic FIB user group 2014 calculation anisotropy • FEM for through-thickness stress gradient analysis; 5 5

Marco Sebastiani FIB M ILLING GEOMETRIES Ring-core Slot-milling Hole drilling method method method Materials Letters 63 Thin Solid Films Nanotechnology (2009) 1961–1963 443 (1-2), pp. 71-77 17, Number 20 , 2006 FIB user E H-bar gF ro Uu G p 2014 Micro-cantilever method 6 Surface & Coatings Technology 215 (2013) 247–252 Acta Materialia 57 (6), 2010 3

Marco Sebastiani K EY - WORD FOR INDUSTRY : AUTOMATION  Only preliminary alignment and focus is required to the operator  E-beam Pt deposition of surface features  Automated patterning/imaging/milling  0° and 52° imaging after each milling step  Automated Correction of ion/electron drift during the test;  All test are initially set  The whole test sequence is through a GUI completed in ½ hour and FIB user group 2014  Geometry multiple test positions can be  Size set for overnight testing;  SEM/FIB parameters  DIC is performed live during 7 test

Marco Sebastiani N EW PATTERNING STRATEGIES FOR IMPROVED DIC  Reduced influence of the Pt-pad  Full strain map over the X-Y plan  Best strain measurement along the fast-scan direction  More effective DIC (resolution of 1/1000 pixel) FIB user group 2014 Freeware DIC runnign 8 on Matlab (C. Eberl)

Marco Sebastiani R ESIDUAL STRESS CALCULATION PROCEDURES 𝜏 0 � � � � � 0 0 𝜏 1 � = � � � 0 𝑪𝝉 = 𝜻 ⇒ �� � = 𝜏 � ⋅ � � 1 ≤ � ≤ � ≤ or 𝜏 2 2 �� 3 � � � 𝜏 3 3 2 1 10 11 � = 0 � � 3 = � � � � 3 � 2 20 21 � 2 � � � � � 30 31 � 3 FIB user group 2014

 Regularisation algorithms for stress depth profile calculation 9

Marco Sebastiani T HE ISSUE OF DEPTH MEASUREMENT  We need to develop accurate calibration procedures for depth measurement.  This is critical in view of an effective residual FIB user group 2014 stress depth profile. 10

Marco Sebastiani A PPLICATION TO THIN FILMS FOR AVERAGE STRESS AND STRESS GRADI ENT ANALYSIS IN THIN FILMS M. Sebastiani, C. Eberl, E. Bemporad, G. M. Pharr Materials Science and Engineering A, 2011 FIB user group 2014 3 µm CAE-PVD CrN on steel AISI M2 11

Marco Sebastiani C RITICAL ISSUES FOR STRESS DEPTH PROFILING  DIC is performed LIVE during the test (e.g. during FIB milling after each SEM imaging step);  Performing AT LEAST five test in a reasonable amount of time (1/2 day)  DEPTH MEASUREMENT is a very critical issue in view of the full automation of the method! FIB user group 2014 12

Marco Sebastiani D EPTH PROFILING OF RESIDUAL STRESS : CrN  Strategy for stress gradient calculation:  fitting with a polynomial expression of the strain data for h/d<0.3  Calculation of the residual stress DEPTH PROFILE by FEM analysis (Integral Method)  Significant gradient of FIB user group 2014 stress is observed from surface to interface on this CrN 13 coating

Marco Sebastiani L OCAL RESIDUAL STRESS FIELD IN THIN FILMS The results consistently show a significant modification of the LOCAL residual stress field induced by the droplet FIB user group 2014 14 Surface and Coatings Technology , 2013

Marco Sebastiani L OCAL RESIDUAL STRESS FIELD IN THIN FILMS How to explain the observed differences: (i) an additional thermal stress factor given by the presence of a metallic droplet (ii) the induced coating re- nucleation process and modification of the growth FIB user group 2014 mechanisms in correspondence of the defect 15 Surface and Coatings Technology , 2013

Marco Sebastiani A PPLICATION ON SUSPENDED MICRO - BRIDGES (MEMS – RF SWITCHES) Sebastiani, M., Bemporad, Korsunsky, A.M. (2010) AIP Conference Proceedings , 1300, FIB user group 2014 16

APPLICATION ON SUSPENDED DOUBLE CLAMPED MICRO-BRIDGES del -400 m- ETD LIME Un1RomaTRE Sebastiani, M., Bemporad, Korsunsky, A.M. AlP Conference Proceedings, 1300, (2010)

APPLICATION ON SUSPENDED MICRO-BRIDGES RF SWITCHES Stress variation over the suspended membrane 500 ......., 450 lU Q.. 400 !. 3 5 0 1 ( / ) ! 300 ( / ) (II ... . . . t 250 (/) jij 200 :J 150 "0 f "Cii T 100 • y (II et:: 50 ' ' ' ' ' ' 0 ' ' 0 100 200 300 400 : 500 600 700 800 from one ' e of the ' D i s ' nce t a : sid membran e (urn) '

Marco Sebastiani A PPLICATION ON AMORPHOUS PLASMA SPRA YED SINGLE - SPLATS ( APPLICATION IN TBC S ) Sebastiani, M., Bolelli, G., Lusvarghi, L., Bandyopadhyay, P.P., Bemporad, E. Surface and Coatings Technology , 206 (23), pp. 4872- 4880 FIB user group 2014 19

Marco Sebastiani A PPLICATION TO AMORPHOUS MATERIALS  Single splats Al 2 O 3 obtained by plasm a spraying FIB user group 2014 Surface and Coatings Technology , 206 (23), pp. 4872-4880 20

Al 2 0 3 splats: Relaxation strain from ring-core incremental milling 2.S E -03 • Test-1 • Test-2 2.0 E -03 • Tes t - 3 .. ...... - o Test-4 -- - - · c : ; n .... o Test - 1 on small splat Ul without c r acking l. S E -03 c: • 0 o Test-2 on small splat 0 · n; without c r acking .... ----- P o l ynomial fitting , . . > < q; l . O E -03 - _ - . { . 0 - - 0 S . OE-04 0 -::::<:0 -- ----6 O . O E +OO :.::....._ .u... ----"' 0 200 400 600 nm ) Milli n g depth from surface ( Small splats (no cracks) o Interpolated strain at 400 nm: +0.38·1 o- 3 ± 0.20·1 o- 3 o Average residual stress: -105.3 ± 55.4 o Elastic modulus by nanoindentation o

Marco Sebastiani C ONCLUSIONS – FIB/DIC METHOD 1/2  A TOOL for micron-scale 3D residual stress analysis on a micron scale has developed and optimized.  Good results The adopted geometry gives high depth resolution  (≈ 1 00 nm ) and lateral spatial resolution (≈ 1 µm ) The developed milling strategies have improved the  repeatability and robustness of DIC procedures LIVE strain depth profiling during FIBing and semi-  automated procedure Calculation of the through thickness stress profile; FIB user group 2014  22

Marco Sebastiani C ONCLUSIONS – FIB/DIC METHOD 2/2  Critical issues to be solved Full automation of the procedure.  Does the FIB induces additional stresses??  Microstructure/anisotropy/plasticity effects??  Careful analysis of elastic properties for stress  calculation. Cross validation with other high-resolution methods  (synchrotron-XRD, EBSD, µ-Raman).  Ongoing work: establishm ent of a standardization activity through a European large project FIB user group 2014 23

Marco Sebastiani ISTRESS E UROPEAN PROJECT  EU project “I STRESS” has started on Jan 1 st 2 0 1 4  Pre-standardization of incremental FIB micro-milling for intrinsic stress evaluation at the sub-micron scale  A new VAMAS TW A and project liaisons with CEN TCs are going to be established FIB user group 2014 24