Introduction to Auger Electron Spectroscopy AES MATSE 305 November 23, 1998

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Introduction to Auger Electron Spectroscopy
(AES)MATSE 305 - November 23, 1998

• Center for Microanalysis of Materials
• Frederick Seitz Materials Research Laboratory
• University of Illinois at Urbana-Champaign

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What is Auger?
Auger Electron Spectroscopy (AES) is a widely
used technique to investigate the chemical
composition of surfaces.
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Why the Odd Name?
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Surface Sensitivity
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The Auger Process
STEP 3 KLL Auger electron emitted to
conserve energy released in step 2
STEP 1 Ejected electron
FREE ELECTRON LEVEL
CONDUCTION BAND
FERMI LEVEL
Auger Transition Named KLL
VALENCE BAND
STEP 3 (alternative) an x-ray is emitted to
conserve energy released in step 2
E(Auger)E(K)-E(L2)-E(L3) E(X-ray)E(K)-E(L2)
L3
L2
2p
L1
2s
STEP 2 L electron falls to fill vacancy
Incident Electron
K
1s
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Auger Energy Scale
The AES instrument measures the kinetic energy
of all collected electrons.
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AES Electron vs. X-ray Photon
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Auger Stats

• Primary Beam 3 - 20 KeV electrons
• Detection Sensitivity 1 atomic
• Sampling Distance (depth) 2 to 4 nm
• Analysis Diameter 80nm to several mm
• Elements Detectable Li and above

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Auger Data Formats
Raw Data
Differentiated Data
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AES Can Identify Elements
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AES Sensitivity Factors
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Peak Height / Quantitation
For quantitation the derivative form of the data
is used. Sensitivity Factors are used to adjust
the peak heights of all elements present in
the sample. The composition is normalized to
100 to determine the amount of each element.
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Additional Capabilities of Auger

• Identify surface contaminants and composition.
• Study composition as a function of depth.
• Analyze sample features as small as 80nm. Using
  an electron gun for the primary beam allows small
  analysis spot sizes.

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Why UHV for Surface Analysis?

Pressure Torr
Degree of Vacuum

• Remove adsorbed gases from the sample.
• Eliminate adsorption of contaminants on the
  sample.
• Prevent arcing and high voltage breakdown.
• Increase the mean free path for electrons, ions
  and photons.

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10
Low Vacuum
-1
10
Medium Vacuum
-4
10
High Vacuum
-8
10
Ultra-High Vacuum
-11
10
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AES Instrument Configuration

• Elements of Typical Auger System
• Electron Gun
• Analyzer
• Secondary Electron Detector
• Ion Gun
• Sample Stage
• Introduction System

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Significance of Primary Beam
The Electron Beam is functioning both as the
imaging beam and the primary beam for analysis.
This means that the area of interest on the
sample can be directly aligned for analysis.
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MRL Instrumentation
PHI Model 660 Scanning Auger Microprobe
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Sputtering Samples
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Al/Pd/GaN Thin Film Example
(cross section)
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Al/Pd/GaN Profile Data
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Al/Pd/GaN Atomic Concentration Data
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Area Specific Depth Profile Example
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Summary of Surface Techniques