Metrology & Inspection Equipment
Film & Composition Metrology
Ellipsometry, XRF, XPS, and SIMS for film characterization
Film Thickness and Composition
Film Thickness and Composition
Key techniques for characterizing deposited films:
- Spectroscopic Ellipsometry (SE): Measures how polarized light changes upon reflection from a film stack. Extracts thickness and optical constants for multiple layers simultaneously. The primary production tool for film thickness (1–10,000 nm range).
- X-Ray Fluorescence (XRF): X-rays excite atoms in the film, which emit characteristic fluorescence. Provides composition and thickness for metal films. Non-destructive and fast.
- X-Ray Photoelectron Spectroscopy (XPS): Measures the binding energies of photoelectrons to determine chemical composition and bonding states of surface layers. Critical for understanding gate stack chemistry.
- SIMS (Secondary Ion Mass Spectrometry): Sputters the surface with an ion beam and analyzes ejected atoms with a mass spectrometer. Gives depth profiles of composition with ppb sensitivity. Destructive but uniquely powerful for dopant profiling.
AFM, TEM, and XRD — When You Need More Than a Spectrum
AFM, TEM, and XRD — When You Need More Than a Spectrum
Spectroscopic techniques give you film thickness and composition averaged over a spot. For the hardest characterisation questions — atom-scale geometry, lattice strain, true surface topography — three workhorse techniques take over:
| Technique | What it measures | Resolution | Throughput | Typical vendor |
|---|---|---|---|---|
| AFM (Atomic Force Microscopy) | 3D surface topography, roughness | ~0.1 nm Z, ~1 nm XY | Slow (offline) | Bruker, Park Systems |
| TEM (Transmission Electron Microscopy) | Cross-section structure, atomic columns | <0.1 nm | Destructive, lab tool | JEOL, Thermo Fisher (Titan) |
| XRD (X-Ray Diffraction) | Lattice spacing, strain, crystallinity, texture | Lattice constants to ~10⁻⁴ | Inline-friendly | Bruker, Rigaku, Jordan Valley |
| XRR (X-Ray Reflectivity) | Film thickness (0.1–200 nm), density, roughness | ~Å thickness | Inline-friendly | Bruker, Rigaku |
Where each is used in a modern fab flow
- AFM — CMP step-height verification, line-edge roughness (LER) for FinFET fins, post-etch sidewall profile checks
- TEM — failure analysis and process development. Focused-ion-beam (FIB) lift-out preps a ~50 nm cross-section that a TEM images at single-atom resolution. Indispensable for the first lots at a new node.
- XRD — measure Ge fraction in SiGe (from peak shift) or strain in epitaxial layers; high-resolution XRD (HRXRD) is the inline tool for epi alloy composition
- XRR — ultra-thin (1–5 nm) film thickness and density; complements ellipsometry where film optical properties are unknown
Key Concept: Why TEM Hasn't Gone Inline
TEM needs an electron-transparent sample, which means a destructive FIB lift-out. Sample prep alone takes hours per site. That's why TEM lives in failure-analysis labs while ellipsometry / OCD / XRR do the inline work on every wafer.
Knowledge Check
Knowledge Check
1 / 2Which technique provides non-destructive film thickness measurement for production monitoring?