Scanning Electron Microscopy (SEM) is a powerful imaging technique that provides detailed, high-resolution images of the surface structures of integrated circuits.
It is widely used in the analysis and quality control of microchip fabrication, allowing engineers to detect defects and verify design patterns at nanometer scales.
SEM is crucial in reverse engineering, failure analysis, and process development. It helps ensure reliability in increasingly miniaturized semiconductor devices.
With SEM, engineers can visualize via structures, metal lines, and dielectric layers with exceptional clarity.
Successful SEM imaging of integrated circuits begins with careful sample preparation. This may involve delayering — a process of sequentially etching away layers of the chip to expose different features. Focused ion beam (FIB) tools are often used in conjunction to achieve high-precision layer removal.
Another key technique is charge mitigation. Because ICs are often made from non-conductive materials, samples may be coated with a thin layer of gold or platinum to prevent charging and enhance image contrast.
Adjusting the accelerating voltage can dramatically affect the level of surface detail captured. Lower voltages (~1–5 kV) are typically preferred for high-resolution surface inspection, while higher voltages are used for cross-sectional imaging.
Keep the working distance short to maximize resolution. Most SEMs will offer the best resolution at working distances between 3–8 mm depending on the lens system. Calibrate your detector settings frequently, and use secondary electron detection for surface morphology and backscattered electrons to highlight material differences.
Drift correction is crucial for long imaging sessions or when observing minute details. Allow the sample stage to stabilize thermally, and consider using image averaging tools for reducing noise.
For automated inspection, use SEM software that supports pattern recognition and overlay features. This enables side-by-side comparison with original layout data, making it easier to spot pattern deviations or missing features.
Energy Dispersive X-ray Spectroscopy (EDX or EDS) is a powerful analytical technique often coupled with SEM to provide elemental composition data. When the SEM’s electron beam interacts with a sample, it generates characteristic X-rays unique to each element, allowing precise identification of materials.
In integrated circuits, EDX is used to detect contamination, identify unknown materials, or verify the elemental makeup of thin films and interconnects. It’s especially valuable during failure analysis when examining residues, corrosion, or unexpected material migration.
Ensure that the sample is properly grounded and has a clean, flat surface to prevent artifacts during EDX mapping. Using lower beam currents can help reduce beam damage, especially when analyzing sensitive or layered materials.
When targeting sub-micron features, minimize interaction volume by operating at lower accelerating voltages and take care to align the detector angle to maximize X-ray collection efficiency.
For layered materials or small regions, consider performing line scans or area maps rather than spot analysis. This provides a clearer understanding of how elements are distributed across specific structures like vias, contacts, and interconnect lines.
