Interaction Electron-Matter
When the electron beam interacts with a sample in a scanning electron microscope (SEM), multiple events happen. In general, different detectors are needed to distinguish secondary electrons, backscattered electrons, characteristic x-rays or induced current. Depending upon the accelerating voltage and sample density, the signals come from different penetration depths.
Auger Electron Spectroscopy (AES) is the best tool for surface contamination analysis (top 50A). The tool provides identification of elements with sensitivities on the order of 0.1% from Lithium through Uranium.
After Auger electrons, the secondary electrons come from the next most shallow penetration depth. A secondary electron detector (SED) collects low-energy (<50 eV) secondary electrons is used to produce a topographic SEM image.
SED images have high resolution that are independent of the material and are acquired from inelastic scattered electrons close to the surface. No material composition information is available.
A backscattered electron detector (BSD) detects elastically scattered electrons. These electrons are higher in energy from atoms below the sample surface. A four-quadrant solid state BSD provides both topography and materials contrast (composition) imaging.
Electron Backscatter Diffraction (EBSD) is an SEM technique used to analyse the diffraction patterns generated when an electron beam interacts with a crystalline sample. The diffraction patterns are imaged on a phosphor screen and analyzed by software to determine the orientation of the crystal structure.
Multi detectors mounted inside a SEM chamber
Electron-beam-induced current (EBIC) is a semiconductor analysis technique useful for evaluating minority carrier properties and defect populations. The inelastic interactions between the electron beam and the semiconductor sample result in the generation of electron-hole pairs. Probe needles are placed in contact with a junction to measure the induced current.
The EBIC system amplifies the point probe measurements and synchronizes them to the electron beam position.One of the limitations of the conventional EBIC technique is that it requires charge collecting junctions which may not be readily available in junctionless samples. In order to measure all those signals, multiple Add-on detectors have to be fitted on the specimen chamber of the Electron Microscope. It is important that these detectors can be installed together on the electron microscope, but do not interfere.
Multi detectors mounted outside a SEM chamber
Most of the detectors are usually mounted on retractable mechanisms featuring high accuracy in repositioning, preventing collisions, and ensuring good reproducibility of the results.
HORIBA Scientific offers a range of Add-on detectors covering panchromatic CL imaging, monochromatic CL imaging, assorted with hyperspectral CL imaging, and/or Raman spectroscopy imaging.