[NanoIC topic] He backscattering analysis of 10B and 11B in a nanometric thin film

In semiconductor technology, boron-doped thin films have attracted significant attention due to their application in advanced CMOS technology. One of the current challenges in this context is the accurate quantification of the concentration of boron. We investigated the quantification of the amount of boron in thin films by combining Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA), and we have shown that the RBS-NRA hybrid approach allowed to quantify the 11B in a boron doped epilayer with a very high accuracy and sensitivity. See references [1] and [2].

It should be noted that natural boron has an isotopic ratio of 11B/ 10B = 4.0  0.1. However, some studies using APT and SIMS suggest that either the isotopic ratio of the supplied boron deviates from this ratio, or that the used analysis methods have mass fractionation effects. Clarifying this ambiguity will be the subject of the Master thesis and is essential to understand the results from various analysis techniques.

As a main technique, you will employ Rutherford backscattering spectrometry (RBS) on a substrate-less boron thin film at the Van de Graaff accelerator. RBS has an excellent mass resolving power and thanks to the removal of the substrate it can differentiate the two boron isotopes. You will build on recent improvements to the set-up to detect the signals of the two isotopes with a much-improved signal-to-noise ratio. Collecting RBS spectra at various energies will allow you to confront the measured backscattering cross section with the theoretical Rutherford equation and to determine the isotopic ratio in the samples. You will interpret the non-Rutherford cross-section behavior for the backscattering of He on boron (11B and 10B) in specific energy intervals in the context of the available literature [3]. If time permits, we will relate the measured isotopic ratio with other methods (e.g., APT, SIMS, ERD).

[1] Q. Bai, M. Dialameh, R.J.H. Morris, I. Vickridge, A. Vantomme, J. Meersschaut, Elastic backscattering during boron implantation in Si1-xGex, Vacuum 219 (2024) 112740

https://doi.org/10.1016/j.vacuum.2023.112740

[2] Q. Bai, M. Dialameh, A.H. Chakkunny, R.J.H. Morris, C. Porret, A. Vantomme and J. Meersschaut, “Quantification of boron in a SiGe epilayer using ion beam analysis”, Applied Surface Science  725 (2026) 165787 https://doi.org/10.1016/j.apsusc.2025.165787