Surface morphology
Secondary electrons are generated near the surface and are useful for pattern shape, edges, and surface roughness.
SEM Principles
How an electron beam becomes an SEM image
SEM is a system where the electron gun, vacuum system, electron lenses, scan coils, detectors, and image processing electronics work together. A focused electron probe scans the sample surface, and generated signals are mapped to position information to form an image.
Beam generation
The electron gun creates a stable emission current, while acceleration voltage determines the electron energy reaching the sample.
Probe reduction and scanning
Condenser and objective lenses reduce the beam into a small probe, while scan coils move it sequentially across the sample surface.
Signal-position mapping
Signal intensity detected at each X-Y position becomes brightness and contrast, revealing surface morphology and composition differences.
System Components
Core modules of an SEM system
Electron gunEmits electrons using source types such as tungsten, LaB6, or FE. Semiconductor inspection requires a stable beam and high resolution even at low landing energy.
Vacuum systemPrevents electron scattering by gas molecules and supports source stability while reducing sample contamination.
Electron lensesCondenser and objective lenses reduce and focus the beam. Probe size affects resolution, signal amount, and depth of focus.
Scanning and image systemScan coils move the beam by position, while signal integration and image processing reduce noise and form the observation image.
Signals
Main signals generated from the sample
Composition and deeper information
Backscattered electrons include relatively deeper information and can show contrast based on atomic number differences.
Elemental analysis
Analyzing characteristic X-rays helps identify elemental information at a defect location or selected area.
Image Formation
How an SEM image is formed
Probe scanning
The electron probe scans X-Y positions on the sample surface sequentially.
ConsultSignal generation
Electron-sample interaction generates signals such as SE, BSE, and X-ray.
TechDetection and amplification
Detectors collect and amplify target signals, then send them to image processing.
ProductsContrast mapping
Signal intensity at each position is converted into pixel brightness to create image contrast.
AppsResolution & Focus
Resolution and depth of focus should be reviewed together
Improving resolution requires a smaller probe size and high-magnification conditions, but signal amount and depth of focus can decrease. For samples with large steps or uneven surfaces, securing enough depth of focus and signal may be more important.
Therefore, SEM review should cover not only required resolution but also sample geometry, step height, observation magnification, signal type, and repeat inspection conditions.