X-ray scattering methods for the analysis of advanced materials

Transcription

1 X-R A Y S C A T T E R I N G S O L U T I O N S X-ray scattering methods for the analysis of advanced materials Joachim F. Woitok Almelo, The Netherlands

2 Contents M a t e r i a l s a n d t h e i r a n a l y t i c a l d e m a n d s X-r a y d i f f r a c t i o n, X-r a y r e f l e c t i v i t y a n d X-r a y d i f f u s e s c a t t e r i n g how it works? X-r a y s o l u t i o n s ( a l l in -on e ) sy ste m

3 X-ray diffraction for today Stress Texture Bulk samples Phase identification/ identification/ quantification quantification Reflectivity/ Diffuse Scattering Loose powders Thin film samples Diffractometer Small amounts Epitaxial layers High-resolution Flat samples Crystallography

4 Analysis of Advanced Materials - Layers P e r f e c t c r y s t a l s n o d e f e c t s, b u t s t r a i n M i s m a t c h e d l a y e r s - r e l a x a t i o n L a r g e m i s m a t c h - h i g h d e n s i t y o f i m p e r f e c t i o n s H i g h l y t e x t u r e d p e r f e c t i o n n o t n e c e s s a r y P o l y c r y s t a l l i n e b u t i t w o r k s P o l y m e r l a y e r s t h e f u t u r e? M e s o s c o p i c m a t e r i a l s c o m i n g u p

5 Thin Film Characterization by X-rays Pseudomorphic epitaxial layers. No defects. Strain may be present Example : AlGaAs/GaAs, SiGe/Si Applications: Lasers, High-frequency IC s Lattice mismatched epitaxial layers. Layers are partly (or fully) relaxed Example: Strained Si, ZnSe/GaAs, InAsSb/GaSb Applications: Blue LED s, IR optopelectronic Layers with large lattice mismatch and/or dissimilar crystal structures Example: GaN/Sapphire, YBaCuO/SrTiO3, BST, PZT Applications: Blue Lasers and LED s, High Tc Superconductors, Ferroelectrics Layers where the epitaxial relationship is weak. Highly textured. Example: AuCo multilayers on Si Applications: Thin film media, heads

6 Structural Characteristics l a t t i c e m i s m a t c h l a y e r t h i c k n e s s s u p e r l a t t i c e s t r u c t u r e Pseudomorphic growth Imperfect epitaxy - - all above, plus - r elax at i on - m osai c spr ead - m i sf i t d i sloc at i on d en si t y - lay er / subst r at e t i lt s Incoherent growth

7 The Crystalline State Atoms, ions, molecules Matter G aseous S t at e Amorphous (disordered) Solid State L i q ui d S t at e Crystalline (ordered)

8 The Crystalline State A c r y st al i s c on st r uc t ed by t h e i n f i n i t e r epet i t i on i n spac e of i d en t i c al bui ld i n g bloc k s. a b Crystal system + Building block Crystal

9 Crystal Lattice and Bragg s Law Crystal X-ray Diffraction θ θ d C B D x x 2 d sinθ =λ Bragg s Law

10 Bragg s Law N N bisects incident and reflected beams Θ Θ θ = angle of incidence = angle of reflection (symmetrical) Bragg Reflection λ is known θ is measured d is calculated λ= 2d sinθ (the wavelength of the x-ray beam) (the reflection angle) (the spacing between the lattice planes)

11 The Ideal Diffraction System Fast exchange of tubes and tube focus positions incident beam optics sam pl e pl atfor m s diffr acted beam optics detector s w ith out r e-al ig nm ent!

12 Bragg-Brentano Powder Diffractometer Detector Receiving slit Soller slits monochromator Curved crystal (Graphite) X-ray tube (line focus) Soller slits Anti scatter slit Beam mask Divergence slit Polycrystalline sample

13 Powder Diffraction Pattern Intensity (counts) Angular Position: d-values Relative intensities: I Theta ( )

14 Powder Diffraction Pattern T h e diffr action patter n is l ik e a fing er pr int of th e cr y stal str uctur e: d v al ues r efl ect th e unit cel l par am eter s ( g r id ) intensities r efl ect th e atom s/ m ol ecul es ( buil ding bl ock s )

15 Lab to Fab Instrument Materials Research Diffractometer (MRD) Sample 4 - Crystal Monochromator X-ray mirror Triple Axis Detector 1 Optic X-ray tube Line focus interchangeable optics PREFIX all kinds of applications High-resolution Reflectivity Thin Film analysis Stress Texture In-plane

16 200 and 300 mm Wafers X P er t P R O E xtend ed M R D X L h h r w h h l l m P r I X m F or ig - esol ution diffr action studies ith ig intensities A ow s ounting of tw o incident beam ef odul es in-l ine

17 X-ray Techniques Experimental techniques scans in reciprocal space rock ing cu rv es ω -2θ scans q scans reciprocal space m apping

18 HR X-Ray Diffraction monochromator (collimator) XRD rocking curve : an unambiguous, standardless measure of the layer composition and thickness counts/s 10M 1M X-ray source SiGe layer Si substrate 100K The accuracy is within a few %. 0.1% Ge 10 ω 10K 1K Omega/2Theta (s)

19 X-ray Reflectivity/ Diffuse Scattering counts/s 100M Plateau: sample size, flatness, instrument 10M Critical edge: density ω 2θ ρ 1M 100K 10K Angular separation: thickness z 1K Shape: roughness, density Omega/2Theta ( )

20 X-ray Reflectivity/ Diffuse Scattering counts/s 100M 10M 2σ ω Fractal model 2θ h=0.9 ρ 1M 100K h=0.5 z 10K 1K roughness vertical correlation 100 z h=0.3 L Sinha et al. (1988) 10 Diffuse scattering Omega/2Theta ( )

21 PreFIX Optical Modules Line focus Line focus 12 mm 0.04 mm 4-crystal Mirror/ Hybrid Point focus 0.4 mm 1.2 mm Lens Mono-cap

22 The PreFIX Concept 14 incident beam P r ef I X mo du l es 8 dif f r acted beam P r ef I X mo du l es H o w can I mak e th e r ig h t co mbinatio ns?

23 Applications Line focus 12 mm 0.04 mm Phase analysis Rocking curve Reflectivity Omega-Stress Point focus 0.4 mm 1.2 mm Psi-Stress Texture Micro-diffraction In-plane diffraction

24 PreFIX X-ray mirror X-ray Mirror

25 X-ray mirror Mirror M l l w p l s u r f etal ic mu til ay er ith ar abo ic ace G r aded d-s p acing al o ng th e mir r o r U s ed w ith l ine f o cu s C o nv er ts div er g ent beam to p ar al l el beam D o es no t co ntr o l ax ial div er g ence

26 X-ray Mirror X-ray mirror parabolic shape mirror quasi-parallel diffracted out-coming beam focus of x-ray tube divergent incident beam beam

27 X-ray Mirror Detector Divergence slits Soller slits X-ray tube (line focus) Parallel Plate Collimator X-ray mirror Samples with uneven surfaces

28 PreFIX Hybrid monochromator What is a Hybrid Monochromator?

29 What is a Hybrid Monochromator? A co mbinatio n o f an X -r ay mir r o r and a ch annel -cu t G er maniu m cr y s tal O nl y C u K α is tr ans mitted P ar al l el, mo no ch r o matic X -r ay beam o f h ig h -intens ity, T w o ty p es : two bounces in the monochromator f our bounces in the monochromator

30 Hybrid monochromator Hybrid Monochromator

31 Performance Comparison Resolution 0.018º 0.015º 0.012º 0.009º 0.006º Si (333) Si (111) Hybrid 0.003º 4x(220 )asym 4x(220 )asym + mirror 4x(220) 4x(220)+ mirror 2* Intensity (log scale) (c/s) Powder diffraction

32 Potential Analyzers for Parallel Beam Set-up Analyzer Resolution Perfect crystal < 0.02 Too narrow Multilayers ? Optimal? Parallel plate collimators > 0.06 Too broad

33 Effect of Diffracted Beam Optics AlGaN/GaN MQW Omega Theta Phi 0.00 Psi 0.00 X Y 0.00 counts/s 10M 1M Hybrid AlGaN/GaN MQW 100K 10K 1K 1mm TA Omega/2Theta (s)

34 High-resolution Diffraction Triple Axis Ge[220] 4 Crystal monochromator X-ray mirror Detector 1 counts/s 10M Beam size: 1.4 x 2.5mm 2 X-ray tube (line focus) Optional slit Detector 2 1M 100K SiGe HBT Si cap SiGe SiGe K Si substrate Ge % 1K Omega/2Theta (s)

35 Analysis of Boron Doping 1M Si x Ge 1-x Si x Ge 1-x Si x Ge 1-x :B Si(004) 100K Si x Ge 1-x 10K Si (001) Si (001) Intensity (a.u.) 1K Omega/2Theta(seconds)

36 Reciprocal Space Mapping (TA) Qy*10000(rlu) SiGe Strained Si Si0.8Ge0.2 Graded SiGe to 20%(relaxed) Si substrate 5x Si(004) SL Ge gradient SiGe Qx*10000(rlu) #1_M1.A

37 2Theta/omega projections: comparison of polycrystalline and single crystal Si Poly silicon 001 silicon wafer !!

38 Set-up Fast Reciprocal Space Mapping X Pert PRO MRD Layer structure Hybrid monochromator X Celerator X-ray tube (line focus)

39 AlGaN/GaN MQW Qy*10000(rlu) X Celerator (total time: 40 min) F2113_7_M1.xrdml GaN (0002) Qx*10000(rlu)

40 Reflectivity Parallel plate collimator Flat crystal monochromator Detector Slit 0.1 mm counts/s 100M 10M 1M 100K 10K Beam size: 0.13 x 5 mm 2 beam knife X-ray mirror Si cap 39.0 nm 38.1 nm 29.4 nm 28.9 nm SiGe SiGe Si substrate X-ray tube (line focus) XRR XRD 54.9 nm 55.1 nm 1K Omega/2Theta ( )

41 Model Based on XRD counts/s 100M 10M 1M 100K Si cap SiGe SiGe Si substrate 10K 1K Omega/2Theta ( )

42 Best Fit Simulation counts/s 100M 10M 1M 100K Si cap SiGe SiGe Si substrate 10K 1K Omega/2Theta ( )

43 Roughness Parameters counts/s 100M 10M 1M 100K 10K 1K L: 45±10nm, h: Omega ( )

44 Thin film phase analysis Thin layers Parallel plate collimator Sample Soller slits X-ray mirror X-ray tube (line focus) Incident angles Detector Depth resolved phase analysis Zn Zn CuGaInSe Zn CuGaInSe CdSe/Mo

45 Ferroelectric Films SBT (SrBi 2 Ta 2 O 9 ) and PZT (Pb(Zr x,ti 1-x )O 3 ) are key materials for: FeRAM (ferroelectric random access memories) MEMS (mircro-electromechanical systems) Goal X-ray characterization: Distinguish cubic non-ferroelectric phase from Pervoskite ferroelectric phase

46 The Material Problem SBT possible phases: Pervoskite Fluorite (low T SBT) Pyrochlore (Bi-deficient composition)

47 X-ray Lens (Point Focus) Detector X-ray tube (point focus) X-ray lens θ = 0.3 Flat graphite crystal monochromator (optional) Stressed and textured samples, highly textured layers

48 Psi- 2Theta/Omega map for phase determination Pt/SBT/Pt/TiO2/SiO2/(100)Si Pyrochlore SBT hkl 65.0 Pt(111) Psi [deg] Pyrochlore (222) Pt(111) Theta/Omega [deg]

49 Texture Stressed and textured samples, Highly textured layers X-ray lens X-ray tube (point focus) Detector Parallel plate collimator θ= = 0.3 Flat graphite crystal monochromator (optinal) Rolled Cu

50 Micro-Diffraction Sample with small area of interest Mono-cap X Celerator θ= 0.3 X-ray tube (point focus) Cu(111) Cu plating 0.4 mm x x

51 In-plane - Low Resolution Setup ω, φ X-ray lens 2θ Crossed-slits slits 0.1 x 5 mm 2 Parallel plate collimator

52 Textured polycrystalline Co(CrPtTa) alloy layers in hard discs Co Cr NiP Al Co-based magnetic thin film typically 25nm thick hexagonal phase highly textured Polycrystalline Cr Co signals lost amongst others Amorphous NiP Polycrystalline textured Al

53 Conventional diffraction geometry vs In-plane The Co reflections, if present, are buried under the NiP amorphous hump. Conventional diffraction Al (200) Amorphous NiP counts/s 800 In-plane diffraction geometry Co(002) Co(002) 600 Co (002) Co (100) Co (101) Co(100) 0 ) C o(1 1 ) 0 C o(1 Co(101) Optics: X-Ray lens, Soller slits, Parallel plate collimator 0 2Theta

54 High temperature studies DHS 900

55 TA Scans as Function of T counts/s 1M 100K Si(004) 700 C 100 C Si_100TA.xrdml Si_150TA.xrdml Si_180TA.xrdml Si_500TA.xrdml Si_700TA.xrdml 10K 1K d 004 [Ang] T [K] Omega/2Theta ( )