RBS routine testing (Rutherford Backscattering Spectrometry) is a non-destructive ion beam analysis technique used to quantitatively determine the elemental composition, film thickness, and depth distribution of thin film materials without the need for reference standards. Our professional laboratory provides fast, accurate, and cost-effective RBS routine testing services for semiconductors, coatings, metals, and advanced materials, supporting R&D, quality control, and failure analysis across industries.
Technical Overview
RBS routine testing refers to the regular, standardized application of Rutherford Backscattering Spectrometry for materials characterization and quality control. RBS is a quantitative ion beam analysis technique in which a monoenergetic beam of light ions, typically 1.5 to 3 MeV helium ions (He⁺ or He²⁺), is directed at a sample surface. A small fraction of these ions undergo elastic collisions with the nuclei of atoms in the sample and are backscattered at a known angle, typically 160 to 170 degrees. By measuring the energy spectrum of the backscattered ions, the masses of the target atoms and their depth distribution can be determined simultaneously.
The technique is distinguished by several key characteristics that make it ideal for routine inspection programs. The backscattered ion energy depends on the mass of the target nucleus, which allows elemental identification, while the gradual energy loss of ions traveling through the sample provides depth information. RBS is inherently quantitative because the scattering cross sections are well known from Rutherford physics, meaning that compositional results can be obtained without matrix-matched calibration standards. The measurement is non-destructive, requires minimal sample preparation, and delivers excellent reproducibility, which is essential for ongoing process monitoring and lot-to-lot quality assurance.
Typical analytical capabilities of routine RBS testing include depth profiling down to approximately 1 to 2 micrometers, depth resolution of roughly 10 to 30 nanometers near the surface, sensitivity in the range of 0.1 to 1 atomic percent for heavy elements, and film thickness measurements with accuracy better than 3 percent. RBS is particularly powerful for detecting heavy elements on light substrates, such as metal films on silicon, and for verifying the stoichiometry of compound films.
Testing Samples
RBS routine testing accommodates a wide variety of solid samples. Because the technique probes only the top few micrometers of material, the sample must have a reasonably flat and smooth surface for optimal depth resolution. Common sample categories submitted for routine RBS inspection include:
Semiconductor Thin Films and Wafers
Silicon wafers, GaAs, InP, SiC, and GaN substrates with deposited or grown layers such as silicides, high-k dielectrics, gate stacks, barrier metals, and epitaxial films. Full wafers and wafer fragments can typically be accommodated up to the chamber size limits of the instrument.
Metal and Alloy Films
Sputtered or evaporated metal layers, multilayer metallization stacks, diffusion barriers such as TiN and TaN, noble metal catalysts, and reflective metal coatings where thickness and interfacial reaction need routine monitoring.
Optical and Protective Coatings
Dielectric multilayers, transparent conductive oxides such as ITO, oxide and nitride hard coatings, and anti-reflective stacks where layer thickness and composition consistency are critical to optical performance.
Compound and Functional Materials
Ferroelectric and piezoelectric films, battery electrode coatings, photovoltaic absorber layers, ceramic films, glass and quartz substrates with functional layers, and ion-implanted materials requiring dose verification.
Sample requirements generally include a flat surface area of at least a few millimeters by a few millimeters, a total sample size compatible with the sample holder (typically pieces up to several centimeters), and dry, vacuum-compatible materials. Powder samples can be analyzed after pressing into pellets or mounting on adhesive carbon tabs.
Testing Items
Standard routine RBS inspection covers the following measurement deliverables:
- Elemental composition and stoichiometry of thin films, reported in atomic percent with quantification traceable to fundamental scattering physics
- Film thickness in nanometers, calculated from areal density (atoms per square centimeter) combined with film density, or directly in areal density when density is unknown
- Depth profiles of individual elements, revealing composition gradients, interdiffusion, and interface mixing
- Ion implantation dose and range verification in semiconductor process control
- Multilayer structure analysis, including individual layer thicknesses and interface sharpness
- Detection of heavy element contamination or inclusion at interfaces and surfaces
- Atom density and areal density measurements for process qualification
- Crystalline quality assessment via ion channeling measurements, including minimum yield determination for epitaxial layers, when requested
Testing Methods
Routine RBS testing at our laboratory follows internationally recognized procedures, including ASTM E2224, the standard guide for elemental analysis depth profiling with RBS, along with internally validated work instructions that ensure consistent, repeatable results. The standard workflow is as follows:
- Sample intake and visual inspection, with documentation of sample history, layer structure expectations, and analytical objectives
- Sample mounting on a clean holder and loading into the high-vacuum analysis chamber, typically at a pressure below 10⁻⁶ torr
- Beam alignment and incidence at normal or near-normal geometry, with backscattered ions detected at a fixed scattering angle using a silicon surface barrier detector or passivated implanted planar silicon detector
- Spectrum acquisition using a 1.5 to 3 MeV helium ion beam, with typical accumulation of sufficient counts for good statistics within 10 to 30 minutes per point
- Spectrum simulation and fitting using recognized analysis software such as SIMNRA or RUMP, applying known stopping powers and scattering cross sections to extract composition, thickness, and depth profiles
- Report generation including the measured energy spectrum, simulation overlay, quantitative composition table, layer thicknesses, depth profiles, and an interpretation of results with measurement uncertainties
Optional enhancements include variable detector geometry for improved depth resolution, glancing-angle geometry for ultra-thin films, heavier probe ions for improved mass separation of light elements, and hydrogen analysis by elastic recoil detection when the light-element content is of interest.
Applications
RBS routine testing is widely deployed across advanced industries where thin film composition and thickness must be verified repeatedly and reliably:
- Semiconductor manufacturing: monitoring silicide formation, high-k dielectric stoichiometry, barrier layer integrity, metal stack thickness, and implanted dose control
- Thin film research and development: validating deposition process recipes, comparing sputtering and evaporation targets, and confirming transfer from lab scale to production
- Optical coating production: verifying layer thickness and composition uniformity across batches for filter and mirror performance
- Photovoltaics and energy storage: characterizing absorber layers, transparent conductors, electrode coatings, and interface diffusion after thermal cycling
- Surface engineering and plating: quality control of plated coatings, anodized layers, nitrided and carburized surfaces
- Academic and materials research: quantitative benchmarking for publications, thesis work, and cross-technique validation of results
- Failure analysis: identifying interdiffusion, oxidation, interfacial reactions, or unexpected contamination as root causes of device or coating failure
FAQ
What is RBS routine testing?
RBS routine testing is the regular use of Rutherford Backscattering Spectrometry to measure the elemental composition, thickness, and depth distribution of thin films and surface layers. It is non-destructive, standardless, and quantitative, making it well suited to recurring quality control and process monitoring.
What elements can RBS detect?
RBS can detect all elements heavier than the probe ion, which means helium-beam RBS is sensitive to elements from carbon and nitrogen upward, with best sensitivity for heavy elements. Hydrogen cannot be measured by conventional RBS but can be quantified using the related ERD technique.
What are the detection limits of RBS?
Detection limits depend on the element and matrix. Heavy elements in a light matrix can be detected down to approximately 0.1 atomic percent, while light elements in a heavy matrix may have limits around 1 to 10 atomic percent due to signal overlap with the substrate.
Is RBS a destructive technique?
No. RBS is essentially non-destructive. The helium ion beam deposits very little energy in the sample, causes negligible sputtering, and leaves the sample intact for subsequent analysis or return to production. Some beam-sensitive organic materials should be evaluated case by case.
What sample size and surface finish are required?
A flat, smooth area of a few square millimeters is typically sufficient. Samples should be vacuum compatible and not outgas. Larger pieces and full wafers can usually be handled within the instrument chamber limits. Rough surfaces degrade depth resolution but can still yield composition data.
How deep can RBS analyze?
With standard helium beams, the analyzable depth is approximately 1 to 2 micrometers. Depth resolution is best at the surface, typically 10 to 30 nanometers, and degrades gradually with depth due to energy straggling.
How does RBS compare with SIMS or XPS?
RBS offers absolute quantification without standards and excellent thickness accuracy, whereas SIMS provides much higher sensitivity for trace impurities and lighter depth profiling capability, and XPS offers superior surface sensitivity and chemical state information. The three techniques are complementary, and combining them gives the most complete picture of a thin film structure.
How long does a routine RBS test take?
A single-point measurement typically requires 10 to 30 minutes of data acquisition, with same-day or next-day reporting available for routine submissions. Multilayer, multi-point, or channeling analyses may require additional time for simulation and interpretation.