High-resolution medium energy ion scattering analysis of semiconductor devices

In the context of the efforts to develop more densely packed and more energy-efficient semi-conductor devices, one recognizes the need for analysis methods to probe the composition with atomic monolayer resolution. Rutherford backscattering spectrometry (RBS) is an established approach in which MeV high-energy ions are incident on the target and the intensity and energy of the scattered particles allow to determine the compositional depth profile of the sample. Yet, the best attainable depth resolution in RBS is of the order of 10 nm, and the sensitivity is of the order of a percentage of a monolayer. A substantially improved resolution and sensitivity in ion beam analysis is therefore sought.

The strategy will be to concentrate on using medium energy ions (of several hundreds of keV for which the energy loss per nanometer is maximized), and on employing a detector with a better energy resolution than is commonly used for RBS.

Essentially, high-resolution Rutherford backscattering spectrometry (HR-RBS) will be pursued by employing a magnetic sector analyzing magnet. It will bring together the resolving power of a magnetic spectrometer and the energy stability of the van de Graaff accelerator at KU Leuven to demonstrate high depth resolution. As a novel approach, the magnetic spectrometer will be equipped with a silicon strip detector to reach high accuracy and superior sensitivity. The study will involve developing the instrument and investigating physics underlying the resolution and quantification capabilities of high-resolution RBS. The unique capabilities of the new approach will be demonstrated by comparison with established analysis methods like RBS, SIMS, XPS and others. The method and its improved capabilities will be first developed and demonstrated on planar thin films and ultra-thin films of technological relevance, and then to study the area-selective deposition of Ru in periodic nanostructures [1].

The study will be elevated by comparing on the same samples the results obtained using the described method and the results obtained with an electrostatic analyzer. For the latter, you will perform experiments at the ion beam center of Helmholtz Zentrum Dresden-Rossendorf (HZDR), Germany [2]. By analyzing the same samples, you will for the first time make a fair comparison of the sensitivity, the background, the measurement speed and the resolution of different high-resolution detection schemes. Ultimately, the comparison may also be made with time-of-flight medium-energy ion scattering (ToF-MEIS), as is for example available in Uppsala, Sweden [3].

Finally, you will also consider phenomena that affect the absolute quantification capability of HR-RBS (besides high depth resolution and sensitivity). For example, the stopping cross section and the charge state equilibrium are known to be energy dependent and to affect the quantification accuracy if not properly modeled.

The study will expose you to the research in a professional semiconductor materials characterization laboratory and give you insights into the physics of beam-solid interactions. You will acquire various experimental skills as well as learn about advanced computational methods for data-analysis including uncertainty estimations.

[1] N. Claessens, et al., Scientific Reports 12 (2022) 17770               
[2] https://www.ionbeamcenters.eu/RADIATE-project-partners/hzdr/
[3] https://www.uu.se/en/centre/tandemlab/infrastructure/