SEM/TEM (Page 2 of 2)

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When performing SEM inspection, the following must be observed:

   
1) The EHT must be high enough to provide a good image but low enough to prevent specimen charging.

 
2) To maximize contrast due to material differences, use as low an EHT as possible.

3) If possible, sputter-coat the specimen to prevent specimen charging. Sputter-coating is considered destructive. Never sputter-coat units that still need to undergo electrical testing, curve tracing, EDX analysis, inspection, etc.

4) The probe current must be set to its default value, unless a higher probe current is needed to focus the point of interest properly.

Fig. 2.  Two examples of Scanning Electron Microscopes

Failure Mechanisms/Attributes Used For: Die/Package Cracks, Die Attach Failures/Defects, Bonding Failures/Defects, Wire Defects/Fractures, Lead Defects/Failures, Foreign Materials on Die/Package, Die Surface Defects, Seal Cracks/Defects, etc.

Transmission Electron Microscopy (TEM)

Transmission Electron Microscopy (TEM) is a technique used for analyzing the morphology, crystallographic structure, and even composition of a specimen. TEM provides a much higher spatial resolution than SEM, and can facilitate the analysis of features at atomic scale (in the range of a few nanometers) using electron beam energies in the range of 60 to 350 keV. 

Unlike the SEM which relies on dislodged or reflected electrons from the specimen to form an image, the TEM collects the electrons that are transmitted through the specimen.  Like the SEM, a TEM uses an electron gun to produce the primary beam of electrons that will be focused by lenses and apertures  into a very thin, coherent beam.  

This beam is then controlled to strike the specimen. A portion of this beam gets transmitted to the other side of the specimen, is collected, and processed to form the image. 

For crystalline materials, the specimen diffracts the incident electron beam, producing local diffraction intensity variations that can be translated into contrast to form an image.  For amorphous materials, contrast is achieved by variations in electron scattering as the electrons traverse the chemical and physical differences within the specimen. 

The greatest consideration when performing TEM analysis is sample preparation.  The quality of sample preparation contributes greatly to whether the micrograph will be good or not, so analysts are required to exercise the necessary diligence in preparing the sample for TEM analysis.

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See Also:  Failure Analysis;  All FA Techniques;  Optical Inspection;  EDX/WDX Analysis

Auger Analysis;  EBIC;  FA Lab Equipment;  Basic FA Flows;  Package Failures;  Die Failures