energy dispersive x-ray spectroscopy (eds/edx)
**Energy Dispersive X-ray Spectroscopy (EDS/EDX)** is an **analytical technique that identifies the elemental composition of materials by detecting characteristic X-rays emitted when a specimen is bombarded with an electron beam** — integrated into SEMs and TEMs as the most accessible and widely used chemical analysis tool in semiconductor failure analysis and process development.
**What Is EDS?**
- **Definition**: When a high-energy electron beam strikes a sample, it ejects inner-shell electrons from atoms. As outer-shell electrons fill the vacancy, characteristic X-rays are emitted with energies unique to each element. An energy-dispersive detector measures these X-ray energies and intensities to identify and quantify the elements present.
- **Range**: Detects elements from beryllium (Z=4) to uranium (Z=92) — covering all elements relevant to semiconductor manufacturing.
- **Detection Limit**: Typically 0.1-1 atomic percent — sufficient for major and minor constituent identification but not trace analysis.
**Why EDS Matters**
- **Contamination Identification**: When a defect or contamination is found on a wafer, EDS immediately identifies which elements are present — pointing to the contamination source.
- **Interface Analysis**: Composition profiling across interfaces (metal/dielectric, gate stack, barrier layers) reveals interdiffusion, reaction products, and composition gradients.
- **Process Verification**: Confirms correct material deposition — verifies that the intended elements are present in the right proportions.
- **Failure Analysis**: Identifies anomalous materials at failure sites — corrosion products, void fillers, foreign materials, and contamination.
**EDS Capabilities**
- **Point Analysis**: Focus beam on a specific location — identify all elements present.
- **Line Scan**: Sweep beam across a line — generate composition profiles showing how elements vary with position.
- **Element Mapping**: Raster beam across an area — create color-coded maps showing spatial distribution of each element.
- **Quantitative Analysis**: Calculate atomic and weight percentages of each element using ZAF or Phi-Rho-Z corrections.
**EDS Specifications**
| Parameter | Modern Silicon Drift Detector (SDD) |
|-----------|-------------------------------------|
| Energy resolution | 125-130 eV at Mn Kα |
| Detection elements | Be (Z=4) to U (Z=92) |
| Detection limit | 0.1-1 at% |
| Spatial resolution | 0.5-2 µm (SEM), 0.1-1 nm (STEM) |
| Analysis speed | 1-60 seconds per spectrum |
| Mapping speed | Minutes to hours per map |
**EDS vs. Other Analytical Techniques**
| Technique | Strengths over EDS | When to Use Instead |
|-----------|-------------------|-------------------|
| WDS (Wavelength Dispersive) | Better resolution, lower detection limit | Overlapping peaks, trace analysis |
| EELS | Better light element, bonding info | TEM thin foil analysis |
| XPS | Surface-sensitive, chemical state | Surface chemistry, oxidation state |
| SIMS | ppb detection limit | Trace contamination, dopant profiling |
EDS is **the first-line chemical analysis tool in semiconductor failure analysis** — providing rapid, non-destructive elemental identification that guides every investigation from contamination source identification to interface characterization and process verification.