The measurement method LAwave, developed at the Fraunhofer IWS, allows non-destructive characterization of films and material surfaces. It uses short laser pulses to create surface acoustic waves. Their propagation velocity is then measured over frequency. The so-called dispersion curve depends on the elastic modulus (Young’s modulus), density, and thickness of the film. After measurement, the dispersion curve is fitted with a physical model to obtain the desired material parameters.
It is also possible to characterize non-coated surfaces, for example gradients of the micro-structure such as machining layers and porosity.
- film thickness from a few nanometers to several hundred micrometers
- film properties from polymer to diamond
- test time less than one minute
- high reproducibility
- easy to use
- simple arrangement
- dimensions of the test area: minimum 5 × 5 mm
- few requirements for the sample geometry
- low effect of surface roughness
- complies with EN 15042-1
In general, all coating and surface properties that affected the propagation of surface acoustic waves can be measured.
Young’s modulus, thickness and density of
- PVD coatings, e.g. DLC, nitrides, carbides, oxides, other ceramics
- CVD coatings and CVD diamond
- thermal-sprayed coatings
- low-k films
- Si, GaAs semiconductors
- polymeric sensor films
- bulk materials, e.g. steel, brass
- cemented carbide
- subsurface damage from silicon wafer processing
- work hardening zone after metal finishing
- surface hardening
The Fraunhofer IWS looks back on many years of experience in developing LAwave measurement systems and software that are used for R&D as well as for quality control throughout the world. Based on a modular designed standard table-top unit, the device can be adapted to customer-specific tasks and sample geometries.
We have distributing partners for Japan, USA, China, and Taiwan, providing sales, service and consulting for LAwave measuring systems to many international customers directly.
Examples of application
- Amorphous carbon coatings (DLC): Young’s modulus correlates with hardness and wear resistance of the coating
- Thermal-sprayed coating: Young’s modulus correlates with crack and pore density, and delamination can be detected. Quality of the coating can be measured on rough, as sprayed surfaces.
- Depth of subsurface damage can be measured, for example on processed silicon wafers after sawing, grinding and polishing. Dispersion curve slope directly correlates with damage depth.
- High-porous low-k films can be measured on suitable substrates: Young’s modulus correlates with resistance against chemical activated polishing process.