lecture 14: introduction to thin film characterization...

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


1 µm

Scanning electron microscopy (SEM)primary e-beam

100-300 keV


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


6,20~108 e/st~10 sL~50 nmI~10 e

d=1.4 nm

Electron Nanodiffraction


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.

lecture 14: introduction to thin film characterization...

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