Auger Electron Spectroscopy Overview

Transcription

1 Auger Electron Spectroscopy Overview Also known as: AES, Auger, SAM 1

2 Auger Electron Spectroscopy E KLL = E K - E L - E L AES Spectra of Cu EdN(E)/dE Auger Electron E N(E) x 5 E KLL Cu MNN Cu LMM E f E N(E) 2p 2s 1s 3/2 1/2 L III L II L I K Incident Beam Kinetic Energy (ev) Note that Auger peaks are typically superimposed on a large background (see red and magenta spectra). For this reason Auger spectra are typically displayed in a differentiated mode as shown in the green spectrum. Detection limits for AES are approximately 0.1 atomic percent. 2

3 Auger Electron and X-ray Emission Energy Dispersive X-ray Spectroscopy (EDX) Auger Electron Emission Auger Auger Electron Electron X-ray X-ray Photon Incident Beam Incident Beam Incident Beam 3

4 AES and EDX AES Provides Superior Nanovolume Analysis Capabilities Primary Electron Beam Primary Electron Beam Characteristic X-rays Auger Electrons Particulate defects EDX Analysis Volume (<1-5 µm) Auger Analysis Volume (5-75 Å) EDX minimum analysis area > 1 µm 710 AES minimum analysis area 8 nm 4

5 AES Analysis Depth Mean Free Path: Mean distance electrons travel before undergoing inelastic scattering 5

6 Analysis Depth Universal Curve 1000 λ (monolayers) nm analysis depth Energy (ev) Typical Auger electron energies 6

7 Auger Electron Spectroscopy Auger Electron Spectroscopy is an analytical technique that provides compositional information from the top few monolayers of a material Detect all elements above He Detection limits: atomic % Surface sensitive: top 5-75 Å Spatial resolution: < 60 Å probe size (PHI 710) 7

8 What Information Does Auger Provide? Surface composition at high spatial resolution Secondary Electron Imaging Provides high magnification visualization of the sample Elemental analysis (spectra) Determines what elements are present & their quantity Elemental imaging (mapping) Illustrates two-dimensional elemental distributions High energy resolution spectra, imaging and depth profiling Chemical state analysis for some materials Sputter depth profiling Reveals thin film and interfacial composition 8

9 PHI 710 Scanning Auger NanoProbe 9

10 PHI 710: Analytical Capabilities Nanoscale image resolution Image registration for high sensitivity Constant sensitivity for all geometries Constant sensitivity with tilt for insulators Nano-volume depth profiling Chemical state analysis 10

11 PHI 710: High Spatial Resolution BAM-L200 Standard Sample AlGaAs Line Width (nm) Locations for Line Scans Area Analyzed 4 nm Al Line Sample provided by Federal Institute for Materials Research and Testing (BAM) Berlin, Germany Ga Map 25 kv - 1 na 256x256 pixels Al Map 25 kv - 1 na 256x256 pixels 1 2 Auger Line Scans hour stability test demonstrating exceptional image registry 11

12 PHI 710: High Spatial Resolution BAM-L200 Standard Sample Line Scan #4 Ga Intensity 4 nm Al Line Al (X3) Distance (µm) 24 hour stability test demonstrating exceptional image registry 12

13 PHI 710: Constant Sensitivity for All Geometries PHI 710 Coaxial Analyzer & Electron Gun Geometry Sensitivity (kcps) 2,000 1,800 1,600 1,400 1,200 1, Sensitivity vs. Sample Tilt Angle Coaxial (CMA) Non-Coaxial (SCA) Tilt Angle (degrees) The CMA with coaxial electron gun provides high sensitivity at all sample tilt angles which is essential for insulator analysis and samples with topography 13

14 PHI 710: CMA with Coaxial Geometry No shadowing Every pixel can be identified as part of a Ni sphere or as part of the In substrate. The Ni particles are complete spheres and the substrate fills in around the particles. Variations in In and Ni intensity provide meaningful compositional information. Secondary Electron Image Ni Map In Map 14

15 Non-Coaxial Geometry Shadowing Many pixels are of unknown composition, apparently neither Ni balls nor In substrate. The Ni particles are not observed as complete spheres and very little of the substrate is seen. Variations in In and Ni intensity do not provide meaningful compositional information. Secondary Electron Image Ni Map In Map 15

16 PHI 710 High Energy Resolution Mode How does the high energy resolution mode work? The CMA energy resolution is given as: ΔE / E = 0.5% An optics element placed between the sample surface and the entrance to the standard CMA retards the Auger electrons, reducing their energy, E From the energy resolution equation, if E is reduced, ΔE is also reduced and so is the Auger peak width; energy resolution is improved The CMA is not modified in any way and retains a 360º coaxial view of the sample relative to the axis of the electron gun US Patent 12 / 705,261 16

17 PHI 710 High Energy Resolution Mode Energy Resolution Specification 0.5 ΔE / E (%) Auger Peak Kinetic Energy (ev) 17

18 PHI 710 High Energy Resolution Mode N(E) cps Al KLL Spectra of Native Oxide on Al Foil Energy Resolution 0.5 % 0.1 % (Al oxide) ev ev (Al metal) Kinetic Energy (ev) 18

19 PHI 710 High Energy Resolution Mode Depth Profile of Zn Oxide on Zn Zn oxide Zn metal x c/s th sputter cycle surface Kinetic Energy (ev) 19

20 PHI 710: Spectral Window Imaging Panel A shows the Si KLL spectrum from the sum of all pixel spectra in the Si KLL Auger image shown in panel B. Panel B shows the three Regions Of Interest (ROI) selected for creation of the basis spectra for Linear Least Squares (LLS) fitting of the Si KLL image data set. Panel C shows the three basis spectra with their corresponding chemical state identifications. Intensity A Composite Si KLL Intensity C Kinetic Energy (ev) Si Oxynitride Si Metal B Si KLL Basis Spectra Silicide Kinetic Energy (ev) Si KLL image with ROI areas 20 µm 20 µm In the spectral window imaging mode, a Si KLL spectrum is collected and stored for each image pixel. 20

21 PHI 710: Spectral Window Imaging Panel A shows a 200 µm A SEI B Si KLL (all Si) C Silicide FOV SEI of a semiconductor bond pad. Panel B shows the Si KLL peak area image from the area of panel A. Panels 20 µm 20 µm 20 µm C, D and E show the 20 µm 20 µm 20 µm chemical state images of silicide, elemental Si and D Si Metal E Si Oxynitride F Si Chemical States Si oxynitride respectively. Panel F shows a color overlay of elemental silicon, silicide and silicon oxynitride images. 20 µm 20 µm 20 µm 20 µm 20 µm 20 µm 21

22 PHI 710: Thin Film Analysis World s best Auger sputter depth profiling Floating column ion gun for high current, low voltage sputter depth profiling Compucentric Zalar Rotation minimizes sputtering artifacts and maximizes depth resolution Image registration maintains field-of-view 22

23 PHI 710: Low Voltage Depth Profiling Improved Interface Definition with use of Ultra Low Ion Energies 500 ev Depth Profile 100 ev Depth Profile Al Al Intensity Ga Intensity Ga As As Sputter Time (min) Sputter Time (min) AlAs/GaAs Super Lattice Thin Film Structure 23

24 PHI 710: Nanoscale Depth Profiling SEI 60 nm Diameter Si Nanowire Surface Spectrum of Nanowire 1 Intensity P O Φ FOV: 2.0 µm 0.5 µm P from the growth gas is detected on the surface of a Si nanowire Si C Atom % Si 97.5 P Kinetic Energy (ev) 20 kv, 10 na, 12 nm Beam 24

25 PHI 710: Nanoscale Depth Profiling 500 V Ar sputter depth profiling shows a nonhomogeneous radial P distribution The data suggests Vapor- Solid incorporation of P rather than Vapor-Liquid- Solid P incorporation Depth Profile of the Si Nanowire Phosphorous (atom %) Sputter Depth (nm) 25

26 PHI 710: Compucentric Zalar Rotation Compucentric Zalar Rotation Axis of Rotation at the Analysis Area Rastered Ion Beam Sample Compucentric Zalar rotation depth profiling defines the selected analysis point as the center of rotation. This is accomplished by moving the sample in X and Y while rotating, all under software control. Zalar rotation is used to reduce or eliminate sputtering artifacts that can occur when sputtering at a fixed angle. Micro-area Zalar depth profiling is possible on features as small as 10 µm with the 710 s automated sample stage. 26

27 PHI 710: Compucentric Zalar Rotation Compucentric Zalar Depth Profile of 10 µm Via Contact Atomic Concentration (%) O Al (metal) Al (oxide) Si Secondary Electron Image (Before Sputtering) Sputter Time (min) 27

28 PHI 710: Compucentric Zalar Rotation Atomic Concentration (%) 100 Depth Profile Comparison With and Without Zalar Rotation Al (metal) 80 O Al (oxide) Si Atomic Concentration (%) Al (metal) O Al (oxide) Si Sputter Time (min) With Zalar Rotation Sputter Time (min) Without Zalar Rotation 28

29 PHI 710: Compucentric Zalar Rotation SE Images of 10 µm Via Contacts after Depth Profiling With Rotation Without Rotation 29

30 PHI 710: Chemical State Depth Profiling Intensity (kcps) Large Area Elemental Depth Profile Ni LMM Si KLL Chemical State of Si? Chemical State of Ni? Sample: Ni deposited on Si substrate Annealed at 425 C Analysis Conditions: As Received 0.1% Energy Resolution 10 kv-10 na 20 µm Area Average Sputter Conditions: 500 V Argon 1 x 0.5 mm raster Sputter Time (min) No Zalar Rotation 10 Sample Tilt 30

31 PHI 710: Chemical State Depth Profiling Si basis spectra extracted from depth profile data set Large area Si chemical state depth profiles created with Linear Least Squares (LLS) fitting Normalized Intensity Si KLL From Si Substrate ev (metal) From Ni layer ev (silicide) Intensity (kcps) Si KLL Si from Ni layer Si from substrate 0 nickel silicide Kinetic Energy (ev) 0.1% Energy Resolution Sputter Time (min) 31

32 PHI 710: Chemical State Depth Profiling Normalized Intensity Ni basis spectra extracted from depth profile data set Ni LMM Ni from Si substrate ev (Ni-silicide) Ni from Ni layer ev (Ni-metal) Intensity (kcps) Large area Ni chemical state depth profiles created with LLS fitting Ni LMM Ni from Ni layer Ni from Si substrate 0 nickel silicide Kinetic Energy (ev) 0.1% Energy Resolution Sputter Time (min) 32

33 PHI 710: Chemical State Depth Profiling Microstructure observed in SEM image after depth profile Φ FOV: 5.0 µm kev 1.0 µm Fe3C 2/16/ Ni Si 1.5 SEM 20kV - 1nA Kinetic Energy (ev) Intensity (Mcps) C Si C Nano-area spectra from selected areas showing islands of nickel silicide Survey Spectra Ni Point 1 Si Si Point 2 22 nm beam size Normalized Intensity Point 2 Si from Substrate ev (metal) Si KLL Spectra Point 1 Si from Microstructure ev (silicide) Kinetic Energy (ev) 0.1% Energy Resolution 33

34 PHI 710: Chemical State Depth Profiling New area on Ni/Si sample with 12 nm removed microstructures visible FOV: 5.0 µm kev 1.0 µm Φ Ni/Si 425C 3/30/2010 SEM 20 kv - 10 na Nano-areas selected for analysis Auger Image Color Overlay 20 kv - 10 na Compositional images show presence of silicide microstructures 34

35 PHI 710: Chemical State Depth Profiling Intensity (kcps) Chemical state depth profile from point #1 - on film (off microstructure) Created with LLS fitting in PHI MultiPak Ni metal Si silicide Ni silicide Si metal Ni/Si film chemical state depth profiling summary: The large area depth profiles unknowingly included heterogeneous distributions of nickel silicide microstructures that grew through imperfections in the Ni film The nano-area depth profile on the Ni film (off microstructures) shows nickel silicide only at the nickel / silicon interface Sputter Depth (nm) 10 kv 10 na 22 nm beam size 35

36 PHI 710 Scanning Auger Nanoprobe Multi-Technique options Energy Dispersive Spectroscopy (EDS or EDX) Backscatter Electron Detector (BSE) Electron Backscatter Diffraction (EBSD) Focused Ion Beam (FIB) The Complete Auger Solution 36

37 PHI 710 Chamber Layout for Options 37

38 PHI 710 Scanning Auger NanoProbe Complete Auger Compositional Analysis for Nanotechnology, Semiconductors, Advanced Metallurgy and Advanced Materials 38