RBS Testing Services: Professional Rutherford Backscattering Spectrometry Analysis

RBS (Rutherford Backscattering Spectrometry) testing is a non-destructive ion beam analysis technique that provides absolute, standards-free quantification of elemental composition, film thickness, and depth profiles in thin films and solid materials. Our professional RBS laboratory serves the semiconductor, coating, photovoltaic, and advanced materials industries with nanometer-scale depth resolution and trace-level detection capability for heavy elements. This article presents a complete overview of our RBS testing services, covering technical principles, sample types, test items, analytical methods, and typical applications.

Technical Overview

Rutherford Backscattering Spectrometry (RBS) is a quantitative ion beam analysis technique in which a collimated beam of light ions, most commonly 1.0 to 3.0 MeV helium ions (He+ or He2+), is directed onto a sample surface under high vacuum. A small fraction of these ions undergo elastic Coulomb scattering (Rutherford scattering) with atomic nuclei in the sample and are backscattered toward a charged-particle detector, typically a silicon barrier or PIPS detector positioned at a backscattering angle of 150 to 170 degrees.

The energy of each backscattered ion carries two pieces of information. First, the kinematic factor, which depends only on the masses of the projectile ion and the target atom, identifies the mass of the element present in the sample. Second, the continuous energy loss of the ion as it travels into and out of the sample provides depth information, enabling non-destructive depth profiling. Because the Rutherford scattering cross sections are known from first principles, elemental areal densities can be determined absolutely from the measured charge and detector geometry without calibration standards, making RBS one of the few truly standardless quantitative analytical techniques.

• Quantification accuracy: typically 1 to 5 percent for areal density and composition
• Depth resolution: approximately 10 to 20 nm with standard silicon detectors, down to a few nanometers with high-resolution magnetic spectrometers
• Analysis depth: approximately 1 to 2 micrometers for helium beams in typical solids
• Detection limits: down to 1E12 to 1E13 atoms per square centimeter for heavy elements in light matrices, approximately 0.01 to 1 atomic percent
• Beam spot size: typically 0.5 to 2 mm, with micro-beam options available for mapping
• Sample damage: negligible for most inorganic materials, classified as non-destructive

RBS is particularly powerful for detecting heavy elements in light matrices, verifying film stoichiometry, measuring absolute film thickness in atoms per square centimeter, and quantifying ion implantation doses. Its main limitation is reduced sensitivity for light elements such as carbon, nitrogen, oxygen, and especially hydrogen in heavy matrices, which can be addressed by complementary ion beam methods such as NRA, HFS, and ERDA described below.

Testing Samples

Semiconductor Wafers and Thin Films

Silicon, compound semiconductor, and other wafer substrates carrying gate oxides, high-k dielectrics (HfO2, ZrO2, La2O3), metal silicides (NiSi, CoSi2, TiSi2), barrier layers (TaN, TiN), and deposited thin metal films are the most common RBS sample type. Full wafer pieces and fragments are accepted, and multi-layer stacks up to the probing depth can be resolved layer by layer.

Metals, Alloys, and Metallization Stacks

Metal films, alloy coatings, plating layers, diffusion barriers, and solder or interconnect metallization can be analyzed for composition, thickness uniformity, and interfacial reaction or intermixing. RBS quantifies elements such as Cu, Al, Ti, W, Ta, Ni, Au, and Pt with high accuracy.

Optical and Protective Coatings

Dielectric and functional coatings including SiO2, TiO2, Ta2O5, Al2O3, Si3N4, ITO, and multilayer optical stacks can be characterized for stoichiometry, thickness, and depth uniformity, which directly govern optical and mechanical performance.

Magnetic Multilayers and Storage Media

Magnetic thin film structures containing Co, Fe, Ni, Pt, Pd, Ru, and rare-earth elements, such as spin valves, tunnel junctions, and perpendicular magnetic recording layers, are routinely measured to verify individual layer thicknesses and interface sharpness.

Ion-Implanted and Processed Materials

Ion-implanted wafers and engineered surfaces can be measured to determine retained dose, peak concentration, and junction depth distribution, and to compare as-implanted versus annealed or processed conditions.

Other Solid Samples

Ceramics, glasses, gemstones, archaeological artifacts, and certain polymers or biological materials can also be analyzed, provided they are vacuum compatible and sufficiently stable under the ion beam.

Testing Items

Our RBS testing services cover the full range of quantitative information that the technique can provide, from surface composition to buried interface structure.

• Quantitative elemental composition (atomic percent) of single layers and multilayer stacks
• Film thickness and areal density in absolute units of atoms per square centimeter, convertible to nanometers using assumed density
• Stoichiometry verification of compounds such as HfO2, TiN, Ta2O5, SiOxNy, Al2O3, IGZO, and perovskite films
• Non-destructive depth profiling of composition versus depth, typically over the top 1 to 2 micrometers
• Interfacial mixing, interdiffusion, and reaction layer quantification after thermal processing or reliability stressing
• Retained ion implantation dose and range verification for As, P, Sb, Ge, and other implanted species
• Heavy element surface contamination and ultra-thin film coverage measurement down to sub-monolayer sensitivity
• Crystalline quality assessment, lattice damage depth profiles, and impurity lattice site location via channeling measurements
• Hydrogen and deuterium content determination via HFS or ERDA configurations

Testing Methods

Standard RBS

The standard configuration uses a 1.5 to 3 MeV helium beam from a tandem or single-ended accelerator, a beam current in the nanoampere range, and a silicon particle detector at a fixed backscattering angle. Random orientation spectra are collected for a defined integrated charge, and the resulting energy spectrum is converted into quantitative depth profiles of all detectable elements heavier than helium.

Rutherford Channeling (RBS/C)

For single-crystal samples such as silicon, GaAs, or SiC wafers, the sample is mounted on a goniometer and aligned so that the ion beam travels along a major crystallographic axis. Comparing aligned and random spectra yields the minimum yield (chi-min), which quantifies crystal perfection, ion implantation damage, and the effectiveness of annealing processes. Channeling also reveals whether impurity atoms occupy substitutional or interstitial lattice sites.

Hydrogen Forward Scattering (HFS)

Because conventional RBS cannot detect hydrogen, the detector is relocated to a forward angle and a thin stopping foil removes scattered helium ions while allowing recoiled protons to pass. This configuration quantifies hydrogen concentration and depth distribution in materials such as silicon nitride, amorphous hydrogenated silicon, DLC coatings, and polymer films.

Elastic Recoil Detection Analysis (ERDA)

ERDA uses a heavier primary ion beam, often chlorine or gold, to recoil light target atoms toward a forward detector. It enables simultaneous depth profiling of hydrogen, deuterium, lithium, boron, carbon, nitrogen, and oxygen in a single measurement, complementing standard RBS for light element quantification.

Spectrum Simulation and Data Modeling

All spectra are fit using internationally recognized simulation software such as SIMNRA and RUMP, applying certified stopping powers and cross section databases. Layer models, interfacial mixing widths, and density assumptions are iteratively optimized to reproduce the measured spectrum, and reported results include estimated uncertainties.

Applications

RBS testing supports research, development, process control, failure analysis, and incoming material qualification across a broad range of advanced technology industries.

• Semiconductor process development: qualification of high-k gate stacks, metal gates, silicide formation, barrier and seed layer deposition, and etch residue analysis
• Ion implantation verification: absolute retained dose calibration for implanters and comparison of implant species distributions before and after annealing
• Thin film and coating manufacturing: stoichiometry and thickness control for optical, wear-resistant, decorative, and tribological coatings
• Photovoltaics and display technology: composition profiling of TCO layers, CIGS and CdTe absorbers, passivation layers, and thin film transistor stacks
• Advanced packaging and interconnects: evaluation of under-bump metallization, diffusion barrier integrity, and intermetallic compound growth
• Magnetic and spintronic devices: layer thickness and interface quality verification in multilayer stacks
• University and institute research: publication-grade quantitative data with full uncertainty analysis and spectrum files supplied for review
• Failure analysis and reliability: detection of interdiffusion, oxidation, contamination, and layer degradation in returned or stressed components

FAQ

Is RBS testing destructive?

For most inorganic materials, RBS is considered non-destructive. The MeV helium beam deposits very little energy in the sample, and wafers or components can generally be returned for further use. Some beam-sensitive organic materials may exhibit slight local modification, which we screen in advance during sample intake.

What elements can RBS detect?

RBS can detect all elements from beryllium upward, but sensitivity depends strongly on the mass difference between the analyte and the matrix. Heavy elements in light matrices are measured with the highest sensitivity, while light elements in heavy matrices have higher detection limits. Hydrogen is invisible to standard RBS and requires HFS or ERDA.

What are the typical detection limits?

Heavy elements in light matrices, for example gold on silicon, can be detected at approximately 1E12 atoms per square centimeter, corresponding to sub-monolayer coverage or roughly 0.001 atomic percent. In matched-mass or heavy matrices, practical detection limits are typically 0.1 to 1 atomic percent for heavy elements and 1 to 10 atomic percent for light elements.

What sample size and preparation are required?

Typical samples are fragments from 5 x 5 mm up to full wafer sections, with a reasonably flat and smooth surface for the best depth resolution. Insulating samples are acceptable and are measured using charge compensation. Samples must be vacuum compatible and free of volatile contamination; no special polishing or coating preparation is required.

How does RBS compare with SIMS, XPS, and EDS?

Compared with SIMS, RBS offers absolute quantification without standards but lower depth resolution and sensitivity. Compared with XPS, RBS probes much deeper and is truly non-destructive, while XPS offers superior surface sensitivity and chemical state information. Compared with EDS in SEM or TEM, RBS provides far better light element quantification and absolute depth information. These techniques are complementary, and we can recommend a combined protocol when needed.

How thick can the films be?

Helium beam RBS provides quantitative depth information over approximately the top 1 to 2 micrometers of a typical solid, depending on density. Hydrogen beam configurations can extend the probing depth, while thicker coatings require combining RBS surface data with cross-sectional microscopy or profilometry.

Can adjacent heavy elements be separated?

Mass resolution decreases with increasing atomic mass, so closely spaced heavy elements such as tantalum and tungsten may overlap in standard spectra. Our engineers apply high-resolution detectors, alternative beam energies, grazing geometries, and constrained simulation models to resolve such overlaps, and will advise if a complementary technique is more suitable.

What is the typical turnaround time?

Standard RBS analysis is completed within 3 to 7 working days after sample receipt, including data acquisition, spectrum simulation, and report issuance. Expedited service within 24 to 48 hours is available upon request, and all reports include spectra, layer models, quantified results, and uncertainty statements.