Characterise thin films using large-area reciprocal-space mapping. With the Bruker EIGER2 R 500K XRD detector, you can map large areas in a realistic timeframe, collecting multiple substrate and film reflections and accurate peak intensities.
Characterise Structural Properties
Even minute variations in epitaxial thin films can significantly affect semiconductor performance. It’s therefore important to accurately measure film properties during manufacturing. Reciprocal space mapping (RSM) with XRD is an ideal technique for characterising the structural properties of thin films:
- Perpendicular and lateral strain
- Composition
- Domain effect
Challenges of Analysing Epitaxial Films
Epitaxial films can be difficult to characterise because of various interrelated structural effects. For example, strain from lattice mismatch can cause peak shifts, but these shifts can also be caused by variations in alloy composition. Peak broadening can be a sign of finite crystallite size, misorientation between domains, strain relaxation with thickness or all three.
While coupled scans and rocking curves provide some of this information, the only way to gain a complete picture is to build a map over reciprocal space. You can also distinguish diffraction peaks from instrumental effects (eg monochromator streaks), avoiding incorrect interpretation of data.
Faster Mapping
To capture a large area of reciprocal space, you need a large detector. The Bruker EIGER2 R 500K can cover a much wider region than would usually be feasible.
The example below consists of 2,061,030 data points, collected by the EIGER 2 in just half an hour. With a standard 0D detector taking 1 second per point, this map would take 572 hours to collect. Even a 1D detector would take 3 hours, so the EIGER2 reduces this time dramatically, making RSM a much more practical option.
The example above is a map of a functional blue LED, taken using the Bruker D8 Discover diffractometer and EIGER2. It consists of a complex quantum well structure with a large mismatch between the substrate and film structure. At close detector-to-substrate distance, multiple substrate and film reflections are observed, allowing measurement of the relaxation of the initial GaN layer relative to the substrate. Pushing the distance back then provided higher resolution, improving peak separation.
Example: Relaxation of Single-Layer Films
In the example below, large-area reciprocal-space maps of two single-layer films were collected with both on-axis and off-axis reflections to determine the degree of relaxation.
Collecting multiple reflections in the same map enables you to easily recognise strain, composition, and tilt effects, without errors caused by variations in sample alignment.
Benefits of Large Area Mapping
With the Bruker EIGER2 R 500K XRD detector, you can cover a wide region of reciprocal space in a realistic timeframe. This means you can fully characterise complex device structures, with multiple substrate and film reflections, even with lattice mismatch.
By changing the sample-to-detector distance, you can balance coverage and resolution to resolve narrowly-spaced film peaks. Capturing on-axis and off-axis reflections simultaneously enables distinguishing between effects that cause peak shifts and broadening, including layer tilt, relaxation, composition, and finite domain size.
You can also perform multiple analyses on each data set to obtain the best possible data. In the example above, Si1-xGex Si1-xGex 113 was used to determine composition and strain, while thickness was measured more accurately from the Si1-xGex x 004 fringes with higher specular intensity.
In addition, the EIGER2’s high dynamic range accurately records intensities, so sections of the map can be extracted for further modelling and fitting.
EIGER2 R 500K XRD Detector
- Versatile hybrid photon counting detector
- Large active area
- Fast RSM collection
- Acquire multiple substrate and film reflections and accurate peak intensities
Further Information
Blue Scientific is the official Nordic distributor of Bruker X-Ray Diffraction systems and detectors. We’re available to answer all your questions and provide quotes – just get in touch:
Contact us on +44 (0)1223 422 269 or info@blue-scientific.com