What is SEM Inspection?

Although we mainly talk about climate testing on these pages , products and materials are also subjected to other types of investigations.

Among these, there are those that focus on sample shapes and sizes which we have analyzed in general in this article.

Today we are talking about one of these procedures: the SEM inspection or SEM test.

How SEM Inspection Works

The English acronym SEM stands for Scanning Electron Microscopy and is, simply put, a method of microscopic investigation.

We are all familiar with ordinary optical microscopes that work by amplifying light through convex lenses. 

But what if there was a much more precise way to obtain reliable data and measurements of very small objects? That's what SEM inspection is for.

In SEM inspection, instead of light we have an electron beam.

Imagine an object falling and leaving its imprint in the sand. The sand is electrons.

The sample being analyzed is struck by the electron beam , and when these electrons hit the surface of an object, they bounce back, providing extremely precise information that is then used to create a detailed image of the object's surface.

There are some caveats to using the SEM. It's not possible to monitor electrons in an ordinary atmosphere. For this reason, SEM testing is always performed in a small thermovacuum chamber.

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What is the SEM Inspection for?

Thanks to SEM, researchers can examine the structure and morphology of objects on a microscopic scale, with a precision and accuracy that is today indispensable in many fields.

Among the fields of application of SEM we can mention:

• Geology and Archaeology: Historical artifacts, rocks, and geological samples are good examples of samples that can be inspected using SEM, reaching a level of analysis that would otherwise be difficult to achieve.

• Medical Research: SEM inspection is also frequently used in medicine on biological tissues and cells, providing valuable information on the structure of cells and proteins and helping to study the effect of drugs and therapies at the cellular level.

• Pharmacological Research: Similarly, SEM is used extensively in pharmacological research to evaluate the form and structure of drugs and active ingredients, ensuring the quality and efficacy of the products.

Many of these procedures are outlined in a number of international standards that address the use of SEM inspection, including: ISO 14966:2002, ISO 13322-1:2014 , and IEC/TS 80004-9:2017.

Conditioning of Materials for SEM Test

Just as vacuum is an essential requirement for a successful SEM inspection, the same can be said for temperature and relative humidity. 

Indeed, substances and materials significantly alter their physical properties depending on environmental conditions. In both granular and microscopic investigations, it's crucial to know the starting conditions of the sample we're analyzing so deeply.

For this reason, it is advisable to climatically condition the sample before carrying out most of the SEM tests.

Climatic chambers, controlled environments in which the temperature and relative humidity can be controlled, are the perfect laboratory tool for this purpose.

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The FDM Climatic Chamber is the ideal professional tool for carrying out the complementary climatic conditioning necessary for a reliable SEM inspection.

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Reference Standards

• ASTM E766 — Standard Practice for Calibrating the Magnification of a Scanning Electron Microscope. Defines the procedure and reference materials (certified graticules) for calibrating magnifications from 10x to 200,000x.
• ASTM E986 — Standard Practice for Scanning Electron Microscope Beam Size Characterization. Methodology for measuring electron beam diameter and spatial resolution.
• ASTM E1508 — Standard Guide for Quantitative Analysis by Energy-Dispersive Spectroscopy (EDS/EDX). Reference for elemental microanalysis coupled to SEM.
• ISO 16700 — Microbeam analysis – Scanning electron microscopy – Guidelines for calibrating image magnification.
• ISO 22309 — Microbeam analysis – Quantitative analysis using energy-dispersive spectrometry (EDS) for elements with atomic number of 11 (Na) or above.
• MIL-STD-883 Method 2018 — Scanning Electron Microscope (SEM) inspection of metallization for military/aerospace semiconductor devices.
• ISO/IEC 17025 — General requirements for the competence of testing and calibration laboratories using the SEM as a certified instrument.

Authoritative Sources

• ASTM International. American standards body that publishes the ASTM E series on electron microscopy and quantitative microanalysis.
• ISO – International Organization for Standardization. Maintains the ISO 16700/22309 series on microbeam analysis and SEM calibration.
• NIST – National Institute of Standards and Technology. Provides certified standards (SRM) for SEM calibration and matrix correction software (DTSA-II).
• ACCREDIA. Italy's sole accreditation body, it oversees the accreditation of SEM laboratories according to ISO/IEC 17025.

SEM Inspection Frequently Asked Questions

What resolution does a modern SEM offer and what does it depend on?

Field emission beam SEMs (FE-SEMs) achieve resolutions of 0.6–1.5 nm at 15 kV and approximately 2–3 nm at 1 kV. Tungsten-filament SEMs stop at 3–5 nm, while Schottky FE-SEMs offer a compromise between 1.5 and 2.5 nm. Resolution depends on: accelerating voltage (higher = smaller beam diameter but greater interaction with the sample), probe current (typically 10–100 pA for high resolution), working distance (optimal 4–8 mm), chamber vacuum quality (≤ 10⁻⁴ Pa), and mechanical stability to prevent vibrations. Calibration according to ASTM E766 uses certified gratings with pitches from 500 nm to 10 μm.

What is the difference between conventional SEM and VP-SEM/ESEM?

The high-vacuum SEM operates at pressures ≤ 10⁻³ Pa, requiring conductive or metallized samples (5-20 nm Au/Pt sputter coating). The Variable Pressure SEM (VP-SEM) operates between 10 and 300 Pa, allowing the inspection of non-conductive samples without coating, thanks to the partial ionization of the gas that neutralizes the charges. The Environmental SEM (ESEM) reaches up to 2,600 Pa with controlled humidity, ideal for hydrated biological samples, pharmaceuticals, and polymers. The tradeoff is the loss of resolution: ESEM typically 3-10 nm versus 1 nm for the conventional SEM. The choice of operating mode depends on the nature of the sample and the type of analysis (morphological, compositional EDS, crystallographic EBSD).

How do you prepare a sample for SEM inspection according to MIL-STD-883?

MIL-STD-883 Method 2018 requires sectioning the device with chemical depassivation (dilute HF/HNO₃ acid) or plasma etching (O₂/CF₄) to expose the metallization. The sample is then mounted on an aluminum stub with conductive carbon tape, followed by 10-15 nm Au-Pd sputter coating if non-conductive. Inspection occurs at 15-20 kV with magnifications of 500x to 10,000x to detect: step coverage < 50%, via voids > 25% area, scratches, or corrosion. Acceptance criteria require photographic documentation with a calibrated reference grating and archived micrographs for the entire batch. The SEM camera must be qualified with a magnification uncertainty ≤ 2% according to ISO 16700.

Which EDS elemental analysis can be combined with SEM?

EnergyDispersive X-ray Spectroscopy (EDS/EDX) coupled to SEM detects elements from beryllium (Z=4) to uranium (Z=92) with detection limits of 0.1-1 wt% and typical energy resolution of 125-133 eV at Mn Kα. Quantitative analysis follows ISO 22309 with ZAF or PhiRhoZ corrections, accuracy of 2-5% relative for major elements (>10% wt) and 10-20% for minor ones. The interaction volume at 20 kV is approximately 1-3 μm³, limiting the spatial resolution with respect to topography. For analysis of thin layers <1 μm, the acceleration is reduced to 5-10 kV. Typical applications: contaminant identification, alloy composition verification, elemental mapping with acquisition time ranging from 30 minutes to several hours depending on the required statistics.