PhD researcher on ion-scattering based compositional tomography

Leuven - PhD
Meer dan twee weken geleden

Quantitative analysis of thin films and nanostructures is a cornerstone in the development of future nanoelectronic devices. For this, Imec is using a high-energy (2 MV) ion accelerator, to perform Rutherford Backscattering Spectrometry (RBS) and other ion scattering techniques. A high energy ion beam impinges on the sample whereby the intensity of the scattered particles and their energy contains information about the elements, their concentration and their depth distribution. Whereas ion scattering techniques are routinely used to characterize nanoelectronic films,  the recent trends towards thinner layers, complex alloys and laterally confined nanostructures, has stimulated fundamental research and developments in order to reach a better depth resolution, unique solutions and ways to characterize 3D-nanostructures.

The first aspect of the PhD will be to explore novel concepts for particle detection such as a magnetic spectrometer in combination with a segmented energy detector (Si based). You will address the underlying physics which affect the depth resolution and quantification accuracy (energy loss, straggling, ...) and assess the uncertainty budget (reduction) by quantifying and minimizing the effects of angular divergence of the incoming beam and backscattered beam, accelerator ripple, energy straggling, sample roughness etc. Your success criteria will to demonstrate a 1-dimensional compositional depth profile with sub-nm resolution in material systems of high importance to the micro-electronics industry.

As for complex systems, the reconstruction of a compositional depth profile from a single RBS spectrum is not unique, a solution can be found by combining (“hybrid metrology”) spectra recorded under different geometries and with various excitation (primary particle backscattering, elastic recoils) and detection (particles, x-rays) schemes. Based on a proper understanding of the underlying physics (HR-RBS, ERD, PIXE), you will parametrize the uncertainties that the various approaches hold with respect to the composition profile and build a framework (minimization process based on maximum entropy?) generating the most probable solution.

As 3D nanostructures become the elemental building block of advanced electronic devices, your goal will also be to realize the first ion-scattering based 3-dimensional composition tomography of a confined nanostructure. The tomography data are derived from a series of RBS spectra that are recorded under varying geometry (primary beam as well as detector positions).  For the reconstruction, you will build upon your experience from hybrid metrology and develop a reconstruction approach based on a generalized 3D-representation of the sample, the scattering geometry in the RBS and methodologies from other tomography fields.  Experimentally, your results will be compared to results on the same nanostructures obtained with atom probe microscopy and TEM tomography.

Required background: engineering technology, engineering science, computer science or equivalent

Type of work: The PhD requires strong mathematical and analytical capabilities, impeccably structured programming, and a swift understanding of the physical principles of the experimental techniques.

Supervisor: Wilfried Vandervorst

Daily advisor: Johan Meersschaut

The reference code for this PhD position is STS1712-51. Mention this reference code on your application form.


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