Scanning Electron Microscopy - Cathodoluminescence (SEM-CL)

Cathodoluminescence (CL) is electromagnetic radiation, or light, ranging from visible (VIS) to near-infrared (NIR) created by the interaction of high-energy electrons (cathode rays) with a luminescent material. The light that is emitted carries very specific information about the optical and electronic properties of the sample.

Using a specialized Scanning Electron Microscope (SEM) that has visible light collection, corresponding sample structure (SE) and CL emission maps can be acquired simultaneously with sub-micrometer resolution. In some cases, the CL spatial resolution can be as good as 30-50 nm. CL mapping can be performed on both cross-sections (XS) or in plan-view (PV) to characterize a sample’s localized composition, doping, structure and defects, all with very high spatial resolutions.

Ideal Uses of SEM-CL

  • Materials characterization – crystalline defects, bandgap determination, intra-bandgap trap states, composition, dopants
  • Semiconductor failure analysis – defect localization within devices for deeper failure analysis (FA)

Strengths of Cathodoluminescence

  • Provides highly localized information about materials optical and electronic properties
  • Does not require electrical connections

Limitations of Cathodoluminescence

  • Requires a luminescent material – semiconductors, polymers, insulators, metal photonic structures
  • Smaller samples required, no full wafers larger than 1” dia – 3 mm height restriction
  • Large amounts of topography, especially non-uniform surface roughness, can make CL collection and contrast interpretation more difficult. Smooth samples are preferred
  • Thick (μms) metal contacts on the surface of a device must be removed before analysis. This can be often done by careful chemical etching or in specific regions by Focused Ion Beam (FIB)
  • Localized dopant characterization is possible but requires careful choice of standards

SEM-CL Technical Specifications

  • Signals Detected: Simultaneous Secondary Electrons (SE) and Cathodoluminescence (CL)
  • Wavelengths Detected: 250-1500 nm
  • Imaging/Mapping: Yes
  • Lateral Resolution: Typically varies from 20-500 nm depending on SEM conditions and sample composition/topology

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