Advanced Materials Characterization Workshop June 3 and 4, 2013

Transcription

1 University of Illinois at Urbana-Champaign Materials Research Laboratory Advanced Materials Characterization Workshop June 3 and 4, 2013 Rutherford Backscattering & Secondary Ion Mass Spectrometery Timothy P. Spila, Ph.D. Frederick Seitz Materials Research Laboratory University of Illinois at Urbana Champaign

2 Rutherford Backscattering Spectrometry He + He RBS is an analytical technique where high energy ions (~2 MeV) are scattered from atomic nuclei in a sample. The energy of the back-scattered ions can be measured to give information on sample composition as a function of depth.

3 Geiger Marsden Experiment Top: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed. Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge.

4 Rutherford Backscattering Spectrometry 2 MeV Van de Graaff accelerator beam size Φ1-3 mm flat sample can be rotated

5 Primary Beam Energy energy loss per cm log(de/dx) 1 kev 1 MeV (log E) 1 kev 1 MeV thin film projected on to a plane: atoms/cm 2 (Nt)[at/cm 2 ] = N[at/cm 3 ] * t[cm] Figure after W. K. Chu, J. W. Mayer, and M. A. Nicolet, Backscattering Spectrometry (Academic Press, New York, 1978).

6 Elastic Two Body Collision Elastic Scattering M 1 v o2 = M 1 v 12 + M 2 v 2 2 M 1 v o = M 1 v 1 + M 2 v 2 K M E 1 = KE o 2 2 sin 2 cos t M i M i M i M t 2 Kinematic factor: K He 4 = 150 o Target mass (amu) M 1 <M 2, 0 θ 180 o 0 Φ 90 o RBS: He backscatters from M 2 >4

7 Rutherford Scattering Cross Section Coulomb interaction between the nuclei: exact expression -> quantitative method M Z Z Z R( E, ) sin ( ) 2( ) 4E 2 M E

8 Electron Stopping energy loss per cm log(de/dx) 1 kev 1 MeV (log E) Figure after W. K. Chu, J. W. Mayer, and M. A. Nicolet, Backscattering Spectrometry (Academic Press, New York, 1978).

9 Kinematic factor: K RBS Simulated Spectra hypothetical alloy Au 0.2 In 0.2 Ti 0.2 Al 0.2 O 0.2 /C Element (Z,M): O(8,16), Al(13,27), Ti(22,48), In(49,115), Au(79,197) (, ) Z R E E He ML 2 = 150 o Target mass (amu) 2 In Au C 10 ML 100 ML Au O Al Ti In Au ML ML C O Al Ti In C O Al Ti

10 SIMNRA Simulation Program for RBS and ERD

11 Thickness Effects Counts 11,500 11,000 10,500 10,000 9,500 9,000 8,500 8,000 7,500 7,000 6,500 6,000 5,500 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1, Energy [kev] nm N, O, Mg interface N surface Channel Ti interface TiN/MgO Series 0 Series 1 Ti surface Scattered D N Incident He 14,000 13,000 12,000 11,000 10,000 Energy [kev] nm Series 0 Simulated 14,000 13,000 12,000 11,000 10,000 Energy [kev] nm Series 0 Simulated Counts 9,000 8,000 7,000 6,000 N surface Counts 9,000 8,000 7,000 6,000 N surface 5,000 4,000 3,000 2,000 1, N, O, Mg interface Channel 450 Ti interface Ti surface 5,000 4,000 3,000 2,000 1,000 0 N, O, Mg interface Channel Ti interface Ti surface

12 Incident Angle Effects Scattered TiN/MgO N Incident He N 14,000 13,000 12,000 11,000 Energy [kev] nm Ti surface Series 0 Simulated 8,500 8,000 7,500 7,000 6,500 Energy [kev] nm Ti surface Series 0 Simulated 10,000 6,000 Counts 9,000 8,000 7,000 6,000 N surface Counts 5,500 5,000 4,500 4,000 3,500 N surface 5,000 4,000 3,000 2,000 1, N, O, Mg interface Channel 450 Ti interface ,000 N, O, Mg interface 2,500 2,000 1,500 1, Channel Ti interface Surface peaks do not change position with incident angle;

13 Example: Average Composition I. Petrov, P. Losbichler, J. E. Greene, W.-D. Münz, T. Hurkmans, and T. Trinh, Thin Solid Films, (1997)

14 RBS: Oxidation Behavior TiN/SiO 2 As-deposited Experimental spectra and simulated spectra by RUMP Annealed in atmosphere for 12 min at T a = 600 C

15 RBS Summary Scattered D N Incident He Quantitative technique for elemental composition Requires flat samples; beam size Φ1 3 mm Non destructive Detection limit varies from 0.1 to 10 6, depending on Z optimum for heavy elements in/on light matrix, e.g. Ta/Si, Au/C Depth information from monolayers to 1 m

16 Secondary Ion Mass Spectrometry SIMS is an analytical technique based on the measurement of the mass of ions ejected from a solid surface after the surface has been bombarded with high energy (1 25 kev) primary ions. Primary Ions Secondary Ions

17 Technique Comparison

18 Block Diagram of SIMS Technique

19 Comparison of Static and Dynamic SIMS TECHNIQUE DYNAMIC STATIC FLUX ~10 17 ions/cm 2 (minimum dose density) < ions/cm 2 (per experiment) INFORMATION Elemental Elemental + Molecular SENSITIVITY TYPE OF ANALYSIS < 1 ppm (ppb for some elements) Depth Profile Mass Spectrum 3D Image Depth Profile 1 ppm Surface Mass Spectrum 2D Surface Ion Image SAMPLING DEPTH 10 monolayers 2 monolayers SPATIAL RESOLUTION Cameca ims 5f Probe mode: 200 nm Microscope mode: 1 m SAMPLE DAMAGE Destructive in analyzed area up to 500 m per area PHI TRIFT III 0.1 m Minimal

20 Magnetic Sector Mass Spectrometer CAMECA ims 5f SECONDARY ION COLUMN PRIMARY ION COLUMN

21 Time of Flight Mass Spectrometer Physical Electronics TRIFT III TOF-SIMS ESA 3 ESA 2 Cs + or O 2 + SED Post Spectrometer Blanker Energy Slit Sample Pre Spectrometer Blanker Contrast Diaphragm ESA 1 Au + ev 1 mv 2 2

22 Ion Beam Sputtering Sputtered species include: Monoatomic and polyatomic particles of sample material (positive, negative or neutral) Resputtered primary species (positive, negative or neutral) Electrons Photons

23 MD Simulation of ion impact Enhancement of Sputtering Yields due to C 60 vs. Ga Bombardment of Ag{111} as Explored by Molecular Dynamics Simulations, Z. Postawa, B. Czerwinski, M. Szewczyk, E. J. Smiley, N. Winograd and B. J. Garrison, Anal. Chem., 75, (2003). Animations downloaded from

24 Quantitative Surface Analysis: SIMS I m s I p y m m In SIMS, the yield of secondary ions is strongly influenced by the electronic state of the material being analyzed. I sm = secondary ion current of species m I p = primary particle flux y m = sputter yield + = ionization probability to positive ions m = factional concentration of m in the layer = transmission of the analysis system

25 Total Ion Sputtering Yield Sputter yield: ratio of number of atoms sputtered to number of impinging ions, typically 5-15 Ion sputter yield: ratio of ionized atoms sputtered to number of impinging ions, 10-6 to 10-2 Ion sputter yield may be influenced by: Matrix effects Surface coverage of reactive elements Background pressure in the sample environment Orientation of crystallographic axes with respect to the sample surface Angle of emission of detected secondary ions + First principles prediction of ion sputter yields is not possible with this technique. Courtesy of Prof. Rockett

26 Effect of Primary Beam on Secondary Ion Yields Oxygen bombardment When sputtering with an oxygen beam, the concentration of oxygen increases in the surface layer and metal-oxygen bonds are present in an oxygen-rich zone. When the bonds break during the bombardment, secondary ion emission process, oxygen becomes negatively charged because of its high electron affinity and the metal is left with the positive charge. Elements in yellow analyzed with oxygen bombardment, positive secondary ions for best sensitivity. Cesium bombardment When sputtering with a cesium beam, cesium is implanted into the sample surface which reduces the work function allowing more secondary electrons to be excited over the surface potential barrier. With the increased availability of electrons, there is more negative ion formation. Elements in green analyzed with cesium, negative secondary ions for best sensitivity. Graphics courtesy of Charles Evans & Associates web site

27 Relative Secondary Ion Yield Comparison From Storms, et al., Anal. Chem. 49, 2023 (1977).

28 Relative Secondary Ion Yield Comparison From Storms, et al., Anal. Chem. 49, 2023 (1977).

29 Determination of RSF Using Ion Implants I m s I p y m m Level Profile: Gaussian Profile: RSF RSF I I m i i I m Ct d Ii di b C Where: RSF = Relative Sensitivity Factor I m, I i = ion intensity (counts/sec) = atom density (atoms/cm 3 ) = implant fluence (atoms/cm 2 ) C = # measurement cycles t = analysis time (s/cycle) d = crater depth (cm) I b = background ion counts

30 Positive and Negative Secondary Ions 10 6 Ion implanted P standard Ion implanted P standard Counts / sec O + beam 2 Si P Cs + beam Si P Concentration (atoms/cm 3 ) O + beam 2 Si P Cs + beam Si P Depth (nm) Depth (nm)

31 Definition of Mass Resolution Mass resolution defined by m/ m Mass resolution of ~1600 required to resolve 32 S from 16 O 2 Graphic courtesy of Charles Evans & Associates web site

32 Depth Profile Application with Hydrogen Detects hydrogen Large dynamic range

33 Isotopic Analysis (a) (a) Ni Al 600 C: 4 h 18 O, 16 h 16 O (a) (b) (c) AES Atomic Concentration (%) Ni Al AES composition depth profile SIMS isotopic oxygen diffusion profile expressed as a percentage of the total oxygen Schematic of layered oxide structure O (b) (c) (b) (c) Oxygen Ion Yield (% Linear Counts) 16 M O M 18 O R.T. Haasch, A.M. Venezia, and C.M. Loxton. J. Mater.Res., 7, 1341 (1992) Sputter Time (min.) NiO M 18 O NiO, NiAl O, Al O M 16 O 16 O + 18 O + Ni Al 3

34 B Depth Profile in Si(001) SIMS depth profiles through a B modulation-doped Si(001):B film grown by GS-MBE from Si 2 H 6 and B 2 H 6 at T s =600 C. The incident Si 2 H 6 flux was J Si2H6 = 2.2x10 16 cm -2 s -1 while the B flux J B2H6 was varied from 8.4x10 13 to 1.2x10 16 cm -2 s -1. The deposition time for each layer was constant at 1 h. G. Glass, H. Kim, P. Desjardins, N. Taylor, T. Spila, Q. Lu, and J. E. Greene. Phys. Rev. B, 61,7628 (2000).

35 Depth Resolution and Ion Beam Mixing SIMS depth profiles through a B -doped layers in a Si(001) film grown by GS-MBE from Si 2 H 6 at T S =700 C. The Si 2 H 6, flux, J Si2H6, was 5X10 16 cm -2 s -1 while the B 2 H 6 flux, J B2H6 varied from X10 14 cm -2 s -1. The inset shows the two-dimensional B concentration N B 2D as a function of J B2H6. Q. Lu, T. R. Bramblett, N.-E. Lee, M.-A. Hasan, T. Karasawa, and J. E. Greene. J. Appl. Phys. 77, 3067 (1995).

36 Static and Dynamic SIMS Dynamic SIMS Static SIMS Material removal Elemental analysis Depth profiling Ultra surface analysis Elemental or molecular analysis Analysis complete before significant fraction of molecules destroyed Courtesy Gregory L. Fisher, Physical Electronics

37 Extreme Mass Range Integral: 1922 TG_SCAN03_NEGSEC_AU2_22KV_BUNCHED_2NA_400UM_90MIN_CDOUT_CHGCOMP_ AMU.TDC - Ions 400µm cts Total Counts Total Counts (9.43 amu bin) Mass (amu)

38 Trace Analysis GaAs Wafer GaOH Si Wafer C 3 H 3 Counts m/ m = 11,600 GaNH 3 Counts K C 2 HN Mass [m/z] Mass [m/z] No sputtering to remove organics on surface. Large C 3 H 3 peak does not have a tail to lower mass which would obscure C 2 HN and K.

39 InAs/GaAs Quantum Dots 15 In + Linescans of Quantum Dots Cts: ; Max: 36; Scale: 1µm µm µm µm

40 GaAs/AlGaAs Depth Profile Al Analysis beam: 15kV Ga + Sputter Beam: 300V O + 2 with oxygen flood Ga

41 Depth Profile Beam Alignment UO U Total_Ion Counts NdO 10 1 Nd Time (Seconds) Total_Ion 10 4 UO U Counts NdO Nd Time (Seconds)

42 TOF SIMS Imaging of Patterned Sample Br O S O O O Si O OH h ( nm) H 2 O H O S O O O Si O OH O O O S Br Br 400 m 400 m 50 m Courtesy Josh Ritchey, Audrey Bowen, Ralph Nuzzo and Jeffrey Moore, University of Illinois

43 TOF SIMS Ion Images of an Isolated Neuron First Images of Vitamin E Distribution in a Cell Courtesy E.B. Monroe, J.C. Jurchen, S.S. Rubakhin, J.V. Sweedler. University of Illinois at Urbana-Champaign

44 TOF SIMS Ion Images of Songbird Brain Selected ion images from the songbird brain. Each ion image consists of ~11.5 million pixels within the tissue section and is the combination of 194 individual 600m 600m ion images prepared on the same relative intensity scale. Ion images are (A) phosphate PO3 (m/z 79.0); (B) cholesterol (m/z 385.4); (C) arachidonic acid C20:4 (m/z 303.2); (D) palmitic acid C16:0 (m/z 255.2); (E) palmitoleic acid C16:1 (m/z 253.2); (F) stearic acid C18:0 (m/z 283.3); (G) oleic acid C18:1 (m/z 281.2); (H) linoleic acid C18:2 (m/z ); and (I) -linolenic acid C18:3 (m/z 277.2). Scale bars = 2 mm. Courtesy Kensey R. Amaya, Eric B. Monroe, Jonathan V. Sweedler, David F. Clayton. International Journal of Mass Spectrometry 260, 121 (2007).

45 Diamond Like Carbon Friction Testing DLC coated ball DLC coated disk Oxygen Carbon C + O Overlay wear tracks and scars formed on DLC coated disk and ball sides during test in dry oxygen Courtesy O.L. Eryilmaz and A. Erdemir Energy Systems Division, Argonne National Laboratory Argonne, IL USA

46 3 D TOF SIMS imaging of DLC Wear track from hydrogenated DLC tested in dry nitrogen Courtesy O.L. Eryilmaz and A. Erdemir Energy Systems Division, Argonne National Laboratory Argonne, IL USA

47 3 D TOF SIMS Movies of DLC NFC6 H2 Environment TOF-SIMS Images Courtesy O.L. Eryilmaz and A. Erdemir Energy Systems Division, Argonne National Laboratory Argonne, IL USA H CH C 2 H C 2 H 2 O

48 SIMS Summary Probe/Detected Species Information Surface Mass Spectrum 2D Surface Ion Image Elemental Depth Profiling 3D Image Depth Profiling Elements Detectable H and above Sensitivity ppb - atomic % Analysis Diameter/Sampling Depth ~1 m - several mm/0.5-1nm

49 Acknowledgments