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 30-50nm. 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
- Material characterization – Crystalline Defects, Bandgap determination, Intra-bandgap trap states, Composition, Dopants
- Semiconductor Failure Analysis – Defect localization within devices for deeper failure analysis (FA)
Technical Specifications
- Signals Detected: Simultaneous Secondary Electrons (SE) and Cathodoluminescence (CL)
- Wavelengths Detected: 250nm – 1500nm
- Imaging/Mapping: Yes
- Lateral Resolution: Typically varies from 20nm-500nm depending on SEM conditions and sample composition/topology
Strengths
- Provides highly localized information about materials optical and electronic properties
- Does not require electrical connections
Limitations
- Requires a luminescent material – semiconductors, polymers, insulators, metal photonic structures
- Smaller samples required, no full wafers larger than 1” dia – 3mm 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 (ums) 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