Fraunhofer Institute for Microstructure of Materials and Systems IMWS
Fraunhofer Institute for Microstructure of Materials and Systems IMWS

Ultrathin layers – methodological expertise in the analysis of quantum nanolaminates and lithography optics

With its focus on high-resolution thin-film analysis, Fraunhofer IMWS offers comprehensive methodological expertise in the characterization of ultra-thin layers in optical coating systems. This can be used, for example, to evaluate nanolaminates (quantum-well structures). The combination of microstructure analysis, chemical characterization, and process understanding helps to shorten development times and offer customers tailor-made solutions.

© Fraunhofer IMWS
HR-TEM image of ultrathin Si layers and SiO2 layers. The sample was provided by the Fraunhofer Institute for Thin Films and Surface Technology IST and is used to compare different deposition parameters with the resulting layer thicknesses [K. Kreuzer, et al., "A-Si/SiO2 nanolaminates for tuning the complex refractive index and band gap in optical interference coatings,” Appl. Opt. 63, 1641–1647 (2024).].
© Fraunhofer IMWS
3D reconstruction of a ToF-SIMS measurement of the Si/SiO2 nanolaminate sample. Even the thinnest layers can still be displayed and evaluated separately in the depth profile.
© Fraunhofer IMWS
HR-STEM bright field image of HfO2 layers (nominal thickness: 2 nm, 1 nm, 0.5 nm) separated by SiO2 (thickness approx. 5 nm). The sample was provided by the Laser Zentrum Hannover (LZH) as part of a project (SHARP) funded by the BMBF.

Analysis of quantum nanolaminates (QNLs) – high-precision multi-layer architectures

Quantum nanolaminates consist of sequences of extremely thin, alternating high- and low-refractive index layers with single-layer thicknesses of less than 1 nm in some cases. They are used to specifically control band gaps and refractive indices, thereby enabling customized optical properties. Important fields of application include optoelectronics (multiple quantum well structures in LEDs, laser diodes, detectors), photonics and integrated optics (mirror systems, filters, resonators), sensor technology, and the development of structured coatings.

In the field of lithography optics, the use of very short wavelengths (13.5 nm for EUV) also requires layer thicknesses and layer thickness accuracies in the sub-nm range. These optics require extremely thin, homogeneous layer packages with atomically smooth interfaces and minimal contamination. They typically consist of multi-layer systems (e.g., Mo/Si periods) in which the layer thicknesses must be precisely controlled in the nanometer range. Fraunhofer IMWS can provide support for the quality control of such structures using a variety of methods.

Insights into layer thicknesses, homogeneity, crystal structure, and interface quality

Working with us, our partners can gain direct insights into layer thicknesses, homogeneity, crystal structure, and interface quality, as well as information on interdiffusion and contamination. Our microstructure-based understanding of processes reduces development times and supports the improvement of the design and manufacture of nanolaminates and lithography optics.

Our customers benefit from our methodological expertise in the following ways:

  • Precise control of layer thickness and microstructural quality of the nanolaminate, separation of individual layers, and detection of diffusion processes
  • In-depth understanding of the relationship between microstructure and optical properties, enabling better design options for refractive index control and bandgap tuning
  • Directly derivable process and manufacturing knowledge that shortens development cycles

The methods used at Fraunhofer IMWS for quality control of ultra-thin layers include:

  • Scanning electron microscopy, including precise cross-section preparation using focused ion beams (FIB-SEM), also combined with energy-dispersive X-ray analysis (EDX), enables imaging of surfaces and cross-sections (cross-section imaging) of stack structures as well as chemical mapping (elemental analysis).
  • High-resolution (scanning) transmission electron microscopy (HR-(S)TEM) provides information about absolute thicknesses, homogeneity, and crystallinity, as well as recognizable interface structures within the stack and, in combination with EDX, element distributions with sub-nm resolution.
  • ToF-SIMS depth profiling identifies contamination and diffusion processes.
  • X-ray photoelectron spectroscopy (XPS) provides information on chemical composition and bonding states and complements the chemical characterization of the boundary layers.

Customized solutions for sample preparation

In addition, extensive expertise in individual sample preparation (grinding, polishing, embedding, sawing, broad ion beam-based cross-section preparation) is available, including FIB-based sample preparation for TEM.

Based on excellent equipment, the highest scientific competence, and an understanding of the needs of industry, we offer a holistic, microstructure-based approach: We not only provide measurement data and evidence, but also reliable statements about structure and chemistry. An added value for our partners is the targeted combination of macro- and microscopic as well as chemical analyses to answer specific questions about nanolaminates and lithography optics – always in close coordination with our project partners to develop individual testing and diagnostic plans and deliver fast, practical results.

(January 14, 2026)