Rutherford Backscattering Spectrometry (RBS) is a powerful, non-destructive ion beam analysis technique for quantitatively determining the elemental composition, thickness, and depth profiles of thin films and near-surface regions of solid materials. Our professional RBS testing solution delivers standard-free quantitative results with nanometer-scale depth resolution, serving semiconductor, coating, and advanced materials industries worldwide.
Technical Overview
Rutherford Backscattering Spectrometry (RBS) is an ion beam analysis technique that measures the energy distribution of high-energy ions, typically helium (He+) or helium ions (He2+), scattered back from the atoms within a sample. When a collimated beam of ions, accelerated to energies between 0.5 and 4.0 MeV, strikes the sample surface, a small fraction undergoes elastic collisions with the nuclei of the target atoms. By measuring the energy of these backscattered ions with a semiconductor detector positioned at a known angle, the technique provides simultaneous information about the mass of the scattering atoms, their concentration, and their depth distribution.
One of the most significant advantages of RBS is that it is an absolute, standard-free quantitative method. The scattering cross sections are well characterized through Rutherford physics, which allows elemental concentrations to be calculated directly from first principles without the need for external calibration standards. The technique offers detection limits ranging from 0.001 to 10 atomic percent depending on the element and matrix, a depth resolution of approximately 5 to 20 nanometers, and a probing depth of up to 1 to 2 micrometers for commonly used helium beams. RBS analysis is non-destructive in most cases, meaning the sample remains intact and suitable for subsequent measurements or continued use in production.
Testing Samples
Semiconductor Thin Films
Silicon-based device structures, silicon dioxide and silicon nitride dielectric layers, high-k gate dielectrics such as hafnium oxide and zirconium oxide, metal silicides including cobalt silicide and titanium silicide, and metal interconnect stacks are routinely analyzed. RBS accurately determines film stoichiometry, thickness uniformity, and interfacial mixing in these advanced electronic structures.
Metal and Alloy Coatings
Protective and functional metallic coatings such as titanium nitride, tantalum nitride, chromium nitride, aluminum oxide, and multilayer metallic stacks can be characterized for composition, thickness, and interdiffusion behavior after thermal processing.
Optical and Functional Thin Films
Transparent conductive oxides such as indium tin oxide (ITO) and aluminum-doped zinc oxide, antireflection coatings, and dielectric mirror stacks benefit from precise stoichiometry verification, since optical performance depends strongly on film composition and density.
Compound Semiconductors and Advanced Materials
Group III-V compound semiconductors such as gallium arsenide, gallium nitride, and indium phosphide, as well as ceramics, glass substrates, and ion-implanted materials, are suitable candidates for quantitative RBS depth profiling.
Testing Items
- Quantitative elemental composition of thin films and bulk near-surface regions
- Film thickness and areal density (atoms per square centimeter) determination
- Depth concentration profiles of individual elements
- Stoichiometry verification of compound films and oxides
- Interfacial reaction and interdiffusion analysis between adjacent layers
- Detection of heavy element impurities in light matrices
- Ion implantation dose and range verification
- Crystal quality and lattice disorder assessment via channeling RBS
- Hydrogen and deuterium content analysis using elastic recoil detection (ERDA/ERD)
Testing Methods
Our laboratory employs a tandem accelerator equipped with a high-precision goniometer and silicon surface barrier or passivated implanted planar silicon (PIPS) detectors. The standard RBS configuration utilizes a 2.0 MeV helium ion beam with the detector positioned at a backscattering angle of approximately 170 degrees to maximize kinematic energy separation between elements. Typical beam currents range from 10 to 50 nanoamperes, and the beam spot size is on the order of 1 to 2 millimeters, ensuring minimal sample damage and representative area-averaged results.
For enhanced sensitivity to light elements or improved mass resolution for heavy elements, the incident energy can be adjusted, or alternative geometries such as glancing-angle detection can be employed to improve depth resolution at the surface. Channeling RBS is performed by aligning the incident beam with a major crystallographic axis of single-crystal samples, which suppresses scattering from the bulk lattice and reveals the concentration of displaced or interstitial atoms, providing critical insight into implantation damage and epitaxial quality.
Acquired energy spectra are simulated and fitted using internationally recognized analysis software based on the SIMNRA algorithm framework, which applies known Rutherford scattering cross sections and stopping powers to model layer structures iteratively until calculated and measured spectra converge. This workflow yields absolute atomic concentrations, layer thicknesses, and interface profiles with a typical compositional accuracy of better than 3 to 5 percent relative.
Applications
RBS testing services support a wide spectrum of industries and research fields where accurate thin film characterization is essential:
- Semiconductor manufacturing: process qualification of deposited layers, silicide formation control, barrier layer integrity, and implant dose calibration
- Optical coating development: composition-optimized deposition processes for filters, mirrors, and antireflective coatings
- Photovoltaics: characterization of absorber layers, transparent electrodes, and interface diffusion in thin film solar cells
- Surface engineering: quality control of hard, wear-resistant, and corrosion-protective coatings
- Metallurgy and plating: coating weight, composition, and interdiffusion assessment for functional plated layers
- Academic and institutional research: quantitative benchmarking data for publications in materials science, physics, and nanotechnology
- Failure analysis: identification of compositional drift, contamination, or unexpected interfacial reactions in defective devices
FAQ
What elements can RBS detect? RBS is sensitive to all elements heavier than the projectile ion. With standard helium beams, this means elements from boron upward, with excellent sensitivity for medium and heavy elements. Hydrogen cannot be detected by conventional RBS but is measured using the related ERDA technique available in our facility.
What is the maximum analysis depth? The probing depth depends on beam energy and sample matrix, typically ranging from several hundred nanometers to approximately 2 micrometers for standard 2 MeV helium RBS.
Does RBS require calibration standards? No. Because scattering cross sections are known from fundamental nuclear physics, RBS provides absolute quantitative results without matrix-matched standards, which is a distinct advantage over many spectroscopic techniques.
Is the technique destructive? RBS is generally considered non-destructive for most inorganic materials. Radiation-sensitive polymers and biological samples may experience minor beam damage, which our engineers evaluate before testing.
What are the sample requirements? Samples should be flat, smooth, and at least several millimeters in lateral dimension, preferably 5 millimeters or larger. Vacuum compatibility is required since analysis takes place at a pressure of approximately 10 to the minus 6 torr. Both conductive and insulating samples can be measured, with charge compensation applied where necessary.
What is the typical turnaround time? Standard RBS analysis results are typically delivered within three to five working days, with expedited service available for urgent engineering or production support needs.