nuclear reaction analysis (nra)
**Nuclear Reaction Analysis (NRA)** is an ion beam technique that quantifies light elements (H, D, ³He, Li, B, C, N, O, F) in thin films and at surfaces by bombarding the sample with an accelerated ion beam and detecting the characteristic nuclear reaction products (protons, alpha particles, gamma rays) produced when projectile ions undergo nuclear reactions with specific target isotopes. Unlike RBS which relies on elastic scattering, NRA exploits resonant or non-resonant nuclear reactions that are isotope-specific, providing unambiguous identification and quantification of light elements.
**Why NRA Matters in Semiconductor Manufacturing:**
NRA provides **isotope-specific, quantitative analysis of light elements** that are difficult or impossible to measure accurately by other techniques, addressing critical needs in gate dielectric, barrier film, and interface characterization.
• **Hydrogen quantification** — The ¹⁵N resonance reaction ¹H(¹⁵N,αγ)¹²C at 6.385 MeV provides absolute hydrogen depth profiling with ~2 nm near-surface resolution and sensitivity of ~0.1 at%, essential for understanding hydrogen in gate oxides, passivation, and a-Si:H films
• **Nitrogen profiling** — The ¹⁴N(d,α)¹²C reaction quantifies nitrogen in oxynitride gate dielectrics (SiON) and silicon nitride barriers with absolute accuracy, calibrating SIMS and XPS measurements
• **Oxygen measurement** — The ¹⁶O(d,p)¹⁷O reaction profiles oxygen through gate stacks and barrier layers, complementing RBS by providing enhanced sensitivity for oxygen in heavy-element matrices (HfO₂, TaN)
• **Boron quantification** — The ¹⁰B(n,α)⁷Li or ¹¹B(p,α)⁸Be reactions measure boron concentration in p-type doped layers, BSG films, and BN barriers with absolute accuracy independent of matrix effects
• **Fluorine profiling** — The ¹⁹F(p,αγ)¹⁶O reaction quantifies fluorine incorporated during plasma processing, ion implantation, or trapped in gate oxides, with sensitivity below 10¹³ atoms/cm²
| Reaction | Target | Projectile | Product Detected | Sensitivity |
|----------|--------|------------|-----------------|-------------|
| ¹H(¹⁵N,αγ)¹²C | Hydrogen | ¹⁵N (6.385 MeV) | 4.43 MeV γ | 0.01 at% |
| ²H(³He,p)⁴He | Deuterium | ³He (0.7 MeV) | Protons | 10¹³ at/cm² |
| ¹⁶O(d,p)¹⁷O | Oxygen | d (0.85 MeV) | Protons | 0.1 at% |
| ¹⁴N(d,α)¹²C | Nitrogen | d (1.4 MeV) | Alpha particles | 0.1 at% |
| ¹⁹F(p,αγ)¹⁶O | Fluorine | p (0.34 MeV) | γ rays | 10¹³ at/cm² |
**Nuclear reaction analysis is the definitive technique for absolute quantification of light elements in semiconductor thin films, providing isotope-specific, standards-free measurements of hydrogen, nitrogen, oxygen, boron, and fluorine that calibrate all other analytical methods and ensure precise compositional control of critical gate, barrier, and passivation films.**