lecture 14: introduction to thin film characterization...
TRANSCRIPT
Lecture 14: Introduction to Thin Film
Characterization: Structural and Chemical Characterization (SEM,
TEM, FIB)
Scanning electron microscopy
INCIDENTELECTRON
STEP 2L electron fallsto fill vacancy
K
L1
L2
L3
FERMILEVEL
FREEELECTRONLEVEL
CONDUCTION BAND
VALENCE BAND
1s
2s
2p
STEP 1Ejected electron
STEP 3KLL Auger electronemitted to conserveenergy released instep 2
STEP 3 (alternative)an x-ray is emittedto conserve energyreleased in step 2
THE AUGER PROCESS
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).
-or-
1O primary e-beam0.5-30 keV
backscattered electrons
secondary electrons<50 eV
Auger electrons
characteristic &bremsstrahlung x-rays
1 µm
Scanning electron microscopy
Reactive ion etching of Al/Si(001)secondary electron image
Scanning electron microscopy SnBi alloysecondary electron image
SnBi alloybackscattered 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
SEM
composite
550 nm
The strongest yellow emission comes from the apex of the elongated hexagonal structure.
CL Image
550 nmCL imaging of cross-sectional view
SEM
Results courtesy of Xiuling Li , Paul W. Bohn, and J. J. Coleman, UIUC
Electron Backscattered Diffraction (EBSP)
Phosphor Screen
Low Light CCD Camera
Camera Control Electronics
Forward Scatter Electron Detector
To SEM
Vacuum Window
Specimen (tilted ~ 70 o to e- beam)
Orientation Mapping and Microtexture
Forward Scattered Electron Image –strong orientation contrast (e--channeling)
Crystal Orientation Mapping
Surface Normal
Local Texture Determination
True Grain ID and Grain Size Determination
Determination of Boundary Character (Misorientation)
Results courtesy of Dan Lillig and Ian Robertson, UIUC
Nickel Alloy
1O primary e-beam0.5-30 keV
backscattered electrons
secondary electrons<50 eV
Auger electrons
characteristic &bremsstrahlung x-rays
1 µm
Scanning electron microscopy (SEM)primary e-beam
100-300 keV
characteristic &bremsstrahlung x-rays
Scanning transmissionelectron microscopy (STEM)
“Coherent”Scattering
(i.e. Interference)“Incoherent”Scattering
i.e. Rutherford
0.18 nm
Analytical Electron Microscopy (STEM/TEM)Analytical Electron Microscopy (STEM/TEM)
“Coherent”Scattering
(i.e. Interference)
“Incoherent”Scattering
i.e. Rutherford
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 bymeasuring energy spectrum of inelascticly scattered electrons.
•• VG HB501 STEMVG HB501 STEM* Cold Field Emission Gun* Gatan PEELS and DigiScan* Oxford ISIS EDS (Low Z)
•• JEOL 2010F (S)TEMJEOL 2010F (S)TEM* Schottky FEG* Image Filter / EELS* EDS (Low Z)
Z contrast, HAADF
G. Håkansson et al, Surface and Coat. Technology, 1991
XTEM/STEM/EDS analysis of interfaces
Advanced analytical TEM/STEM
110n
m
O K-Edge
Ni L2,3-Edge0 10 20 30 40 50 60 70 80 90 100 110
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Ni/O Ratio
Ni/O
Rat
io
Position (nm)
BG
Sub
tract
ed C
ount
s (A
.U.)
525 530 535 540 545 550 555 560 565 570
Energy (eV)
20nm20nm20nm
855 860 865 870 875 880
Energy (eV)
BG
Sub
tract
ed C
ount
s (A
.U.)Ni/O Atomic Ratio
Bulk
Surface
Bulk
Surface
35nm
Nano-area electron diffraction
Front Focal Plane
Back Focal Plane
Specimen Plane
FEG Source200kV
Cond 2
Mini Lens
Upper ObjectiveField
Lower ObjectiveField
Projector System
Cond 1
C1 ApertureFixed
C2 Aperture10µm
e-
nm
0
200
400
600
800
e-
0 10 20 30 40nm
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
M. Gao, J.M. Zuo, R.D. Twesten, I. Petrov, L.A. Nagahara & R. Zhang, Appl. Phys. Lett. 82, 2703 (2003)
6,20~108 e/st~10 sL~50 nmI~10 e
d=1.4 nm
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, orThe dual-beam focused ion beamElectron 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
• 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.
• Layout of the focused ion beam 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 growthnucleation 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.