rutherford backscattering spectrometry (rbs)
**Rutherford Backscattering Spectrometry (RBS)** is a quantitative, non-destructive ion beam analysis technique that determines elemental composition, depth distribution, and film thickness by directing a beam of light ions (typically 1-3 MeV He⁺) at a sample and measuring the energy spectrum of ions backscattered from atomic nuclei. The energy of backscattered ions depends on the target atom mass (kinematic factor) and depth (energy loss), providing simultaneous composition and depth information without reference standards.
**Why RBS Matters in Semiconductor Manufacturing:**
RBS provides **absolute, standards-free quantification** of thin-film composition and thickness with ±1-3% accuracy, making it the reference technique for calibrating other analytical methods used in semiconductor process control.
• **Film thickness measurement** — RBS determines thickness in atoms/cm² directly from the peak area, convertible to nanometers using bulk density; accuracy of ±1-2% without reference standards makes it the primary calibration technique for ellipsometry and XRF
• **Composition quantification** — Backscattered energy identifies elements by mass with no matrix effects; peak height ratios give absolute stoichiometry (e.g., HfₓSiᵧOᵤ films) without sensitivity factors or reference materials
• **Depth profiling** — Energy loss through the film creates a continuous depth profile with ~5-10 nm depth resolution; no sputtering required, preserving the sample for additional analysis
• **Channeling (RBS/C)** — Aligning the beam with crystal axes dramatically reduces the backscattered yield from lattice atoms; displaced atoms (dopants, damage) at interstitial sites remain visible, enabling quantification of crystal damage, dopant substitutionality, and epitaxial quality
• **High-k dielectric characterization** — RBS quantifies Hf, Zr, Al, and La content in gate stacks with absolute accuracy, determining stoichiometry and interfacial layer composition without assumptions about film density
| Parameter | Typical Value | Notes |
|-----------|--------------|-------|
| Beam | 1-3 MeV He⁺ (⁴He²⁺) | Standard analysis beam |
| Beam Current | 10-50 nA | Higher current = faster analysis |
| Spot Size | 1-2 mm | Millimeter-scale average |
| Depth Resolution | 5-10 nm | Surface; degrades with depth |
| Accuracy | ±1-3% | Absolute, no standards needed |
| Sensitivity | ~0.1 at% (heavy in light) | Poor for light elements in heavy matrix |
**RBS is the semiconductor industry's primary reference technique for absolute thin-film composition and thickness measurement, providing standards-free quantification with unmatched accuracy that calibrates all other analytical methods and ensures reliable process control for critical gate dielectric, barrier, and electrode films.**