Auger Electron Spectroscopy (AES)

Auger Electron Spectroscopy (AES)/Scanning Auger Microscopy (SAM)

Introduction to Auger Analysis

Scanning Auger microscopy (SAM) is also known as Auger electron spectroscopy (AES).  In this technique, the sample surface is bombarded with a primary electron beam (3 to 25 keV), which results in the emission of secondary, backscattered and Auger electrons from the area of bombardment, and these can be readily detected and analyzed.  The secondary and backscattered electrons are used for imaging purposes similar to scanning electron microscopy (SEM).  The Auger electrons are emitted at discrete energies that are characteristic of the elements present on the sample surface.  The characteristic energies of the Auger electrons are such that only the electrons from the outer 0.5 to 5 nm can escape and be detected.  This makes SAM an extremely surface sensitive technique and, combined with high spatial resolution, the analysis volume is typically 106 to 108 times smaller than that excited in SEM/EDX analysis.  All elements in the periodic table, except hydrogen and helium, can be detected and their concentration can be determined.  The detection limit is typically 500 to 2000 ppm depending on the element.

Using an Ar+ ion beam to sputter or etch away the outer surface layers in a controlled manner, the freshly exposed surface can be analysed and its composition can be determined.  By repeating this process, a plot of concentration versus sputter depth (known as depth profiling) can be created.  Depth profiles can be used to estimate the thicknesses of the oxide layers and thin films, and to determine the variations in composition through thickness.  By monitoring intensity distributions for selected elements over the area of interest, surface-sensitive elemental intensity distribution maps can be obtained.  Other types of Auger analyses include single and multi-point analysis, line scans and acquisition of spectra in high-resolution mode so that chemical state information can be determined from the high-resolution spectra.

Applications of SAM include small-spot, surface-sensitive materials characterization, determination of the composition and the thickness of the corrosion products and thin films, evaluation of fracture surface morphology and chemistry, analysis of thin stains, small particles, and other features on semiconductor component surfaces, analysis of polymeric and other organic materials, and evaluation of the surface chemistry on mineral samples.

Instrument:

Physical Electronics Model 710 Field Emission Scanning Auger Nanoprobe

System Capabilities:

  • High-resolution secondary electron imaging, < 4 nm spatial resolution
  • Small-spot Auger analysis, < 8 nm spatial resolution
  • Floating ion gun enables fast sputtering with least damage and charge neutralization.
  • Survey scan analysis of elements from Li to U at outer 0.5 – 5 nm of the surface
  • Depth profiling (Ar+ ion gun, 50 ev to 5 kV)
  • Surface-sensitive mapping to determine the presence and spatial distribution of elements at the very outer surface
  • Single and multi-point analysis
  • Can accommodate samples of 50 mm in diameter and 1 cm tall
  • Auger analysis can be conducted on metals and alloys, semiconductors, minerals, polymers and glasses.
  • Charge neutralization can be utilized for analyzing insulating samples

Selected Applications in Industry:

  • Small spot surface-sensitive analysis to determine surface composition and chemical state of the elements present
  • Determination of the composition through the thickness of oxide layers and thin films
  • Determination of their thickness
  • Morphology of oxides on nickel-alloy sample
  • Composition of a multi-layered structure
  • Stain on gold-plated lid
  • High contact resistance in relay contacts (Ag-Sn-In alloy)
  • Hazy region found on a chrome-plated part
  • Stain found on Inconel 690 sample
  • Dark-coloured contaminants on aluminum wire bond pads