Lecture 14: Introduction to Thin Film Characterization: Structural and Chemical Characterization (SEM, TEM, FIB)

Lecture 14: Introduction to Thin Film Characterization: Structural and Chemical Characterization (SEM, TEM, FIB)

Scanning electron microscopy

Scanning electron microscopy secondary electrons <50 ev 1 O primary e-beam 0.5-30 kev backscattered electrons Auger electrons characteristic & bremsstrahlung x-rays 2p THE AUGER PROCESS STEP 1 Ejected electron CONDUCTION BAND VALENCE BAND -or- STEP 3 KLL Auger electron emitted to conserve energy released in step 2 FREE ELECTRON LEVEL FERMI LEVEL L3 L2 STEP 3 (alternative) an x-ray is emitted to conserve energy released in step 2 2s 1s L1 STEP 2 L electron falls to fill vacancy K INCIDENT ELECTRON 1 µm The emitted Auger electron is designated the (core hole) (step 2 level) (step 3 level) transition ie. (KLL) transition. The kinetic energy of the emitted Auger electron is : E(Auger) = E(K) - E(L2) - E(L3). The energy of the emitted X-ray is : E(X-ray) = E(K) - E(L2).

Scanning electron microscopy SnBi alloy secondary electron image SnBi alloy backscattered electron image Reactive ion etching of Al/Si(001) secondary electron image

X-ray Microanalysis in the SEM Qualitative elemental analysis From boron up on periodic table Sensitivities to 0.1 wt. % Depending on matrix and composition Quantitative analysis Standardless With standards Digital elemental distribution imaging and linescans

Cathodoluminesence Imaging and Spectroscopy Optical spectroscopy from 300 to 1800 nm Panchromatic and monochromatic imaging (spatial resolution - 0.1 to 1 micron) Enhanced spectroscopy and/or imaging with cooled samples (liq. He) Applications include: Semiconductor bulk materials Semiconductor epitaxial layers Quantum wells, dots, wires Opto-electronic materials Phosphors Diamond and diamond films Ceramics Geological materials Biological applications

Cathodoluminesence of GaN Pyramids CL Image composite SEM 550 nm 550 nm CL imaging of cross-sectional view SEM The strongest yellow emission comes from the apex of the elongated hexagonal structure. Results courtesy of Xiuling Li, Paul W. Bohn, and J. J. Coleman, UIUC

Electron Backscattered Diffraction (EBSP) Low Light CCD Camera Vacuum Window Phosphor Screen Forward Scatter Electron Detector To SEM Specimen (tilted ~ 70 o to e - beam) Camera Control Electronics

Orientation Mapping and Microtexture Nickel Alloy Crystal Orientation Mapping True Grain ID and Grain Size Determination Local Texture Determination Determination of Boundary Character (Misorientation) Forward Scattered Electron Image strong orientation contrast (e - -channeling) Surface Normal Results courtesy of Dan Lillig and Ian Robertson, UIUC

Scanning electron microscopy (SEM) 1 O primary e-beam 0.5-30 kev Scanning transmission electron microscopy (STEM) primary e-beam 100-300 kev secondary electrons <50 ev backscattered electrons Auger electrons characteristic & bremsstrahlung x-rays characteristic & bremsstrahlung x-rays 0.18 nm 1 µm Coherent Scattering (i.e. Interference) Incoherent Scattering i.e. Rutherford

Analytical Electron Microscopy (STEM/TEM) Coherent Scattering (i.e. Interference) Incoherent Scattering i.e. Rutherford VG HB501 STEM * Cold Field Emission Gun * Gatan PEELS and DigiScan * Oxford ISIS EDS (Low Z) JEOL 2010F (S)TEM * Schottky FEG * Image Filter / EELS * EDS (Low Z) EDS (Energy Dispersive Spectrometry)- Quantitative compositional information by measuring energy and number of x-rays emitted from the specimen. Best for higher Z elements. EELS (Electron Energy-Loss Spectrometry) - Both quantitative compositional, and local bonding and coordination information by measuring energy spectrum of inelascticly scattered electrons.

Z contrast, HAADF

XTEM/STEM/EDS analysis of interfaces G. Håkansson et al, Surface and Coat. Technology, 1991

Advanced analytical TEM/STEM

20nm 35nm 110nm O K-Edge BG Subtracted Counts (A.U.) Bulk Surface 525 530 535 540 545 550 555 560 565 570 Ni/O Ratio 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 Ni/O Atomic Ratio Ni/O Ratio 0 10 20 30 40 50 60 70 80 90 100 110 Ni L 2,3 -Edge BG Subtracted Counts (A.U.) Energy (ev) Bulk Surface 855 860 865 870 875 880 Energy (ev) Position (nm)

Nano-area electron diffraction FEG Source 200kV Cond 1 Cond 2 C1 Aperture Fixed C2 Aperture 10µm Mini Lens Upper Objective Field Lower Objective Field Projector System Front Focal Plane Specimen Plane Back Focal Plane e- 800 600 400 200 0 0 10 20 30 40 nm M. Gao, J.M. Zuo, R.D. Twesten, I. Petrov, L.A. Nagahara & R. Zhang, Appl. Phys. Lett. 82, 2703 (2003)

Determination of Individual CNT Structure ~10 8 e/s t~10 s L~50 nm I~10 e 6,20 d=1.4 nm M. Gao, J.M. Zuo, R.D. Twesten, I. Petrov, L.A. Nagahara & R. Zhang, Appl. Phys. Lett. 82, 2703 (2003)

Electron Nanodiffraction M. Gao, J.M. Zuo, R.D. Twesten, I. Petrov, L.A. Nagahara & R. Zhang, Appl. Phys. Lett. 82, 2703 (2003)

CNT atomic structure and super-resolution J.M. Zuo, I. Vartanyants, M. Gao, R. Zhang and L.A. Nagahara, Science, 300, 1419 (2003)

The dual-beam electron/ion microscope, or The dual-beam focused ion beam Electron column Ion column Pt doser The FEI Dual-Beam DB-235 Focused Ion Beam and FEG-SEM has a high resolution imaging (6nm) Ga + ion column for site-specific cross-sectioning, TEM sample preparation, and nano-fabrication. It also has a high resolution (<1.5 nm) Scanning Electron Microscope (SEM) for imaging prior to, during, and after milling with the ion beam. It is also equipped with beam activated Pt deposition and an Omniprobe in-situ nanomanipulator.

Ion Microscopy: Ions and Electrons Layout of the focused ion beam system The gallium ion beam hits the substrate thereby releasing secondary electrons, secondary ions and neutral particles. The detector can build an image from the secondary electrons. For deposition and etching: gases can be injected to the system.

Transmission electron microscopy sample preparation Step 1 - Locate the Area of Interest Step 2 - FIB-deposit a Protective Tungsten or Platinum Layer Step 3 - Mill Initial Trenches & Rough Polish Step 4 - Thin the Central Membrane Step 5 - Perform "Frame Cuts" on Central Membrane Step 6 - "Polish Mills" to Near Nominal Thickness Step 7 - Polish for Electron Transparency of Membrane Step 8 - FIB-mill to Free Membrane from Trenches

Transmission electron microscopy sample preparation (cont.) An in-situ micromanipulator Omni-probe - allows the TEM sample to be extracted (top left), mounted (bottom left) and thinned (bottom right) on a grid for analysis in the TEM.

Photonic Array: A seed layer for photonic cell crystal growth nucleation fabricated with the FIB Cross sectional views can be easily created using the FIB allowing subsurface observation. This corrosion experiment shows the extent of the subsurface corrosion in an aluminum alloy. Pt Dot: This Platinum dot is used as an etch mask in porous silicon experiments.