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Localized ion beam mixing using a focused Neon beam for future SET applicatons

Xu, X.; Hlawacek, G.; Wolf, D.; Engelmann, H.-J.; Prüfer, T.; Hübner, R.; Bischof, L.; von Borany, J.; Facsko, S.; Heinig, K.-H.


The increased use of personal computing devices and the Internet of Things (IoT) is accompanied by a demand for a computation unit with extra low energy dissipation. The Single Electron Transistor (SET), which uses a Coulomb island to manipulate the movement of single electrons, is a candidate device for future low-power electronics. However, so far its development is hindered by low-temperature requirements and the absence of CMOS compatibility. By combining advanced top-down lithography with botom-up self-assembly of Si nano dots (NDs) we will overcome this barrier.
In this work, Si NDs—suitable as RT Coulomb islands—are formed via ion beam mixing followed by thermally stimulated phase separation. Spatial control over the ND formation is achieved by using the highly focused Neon beam with a diameter of only 2 nm available in the helium ion microscope (HIM).
The impinging energetic ions will locally mix excess Si from a top Si-layer and into a buried SiO 2 layer which is grown on a Si wafer. This results in a mixing volume small enough for restricted Ostwald ripening and successful single ND formation. The formation of spatially controlled single NDs with a diameter of only 2.2 nm is confrmed by comparing the energy fltered transmission electron microscopy (EFTEM) Si plasmon-loss intensity with simulated plasmon loss images. The conditions for ND formation, namely the dependence on primary energy, irradiation fuence, layer thickness and thermal budget during rapid thermal annealing (RTA), are optimized based on an extensive survey of this multidimensional parameter space. The investigation is guided by TRIDYN simulations of the Si excess in an SiO 2 layer due to ion beam mixing and 3D Kinetic Monte-Carlo (3DkMC) simulation for the phase separation during the thermal treatment. To achieve a CMOS compatible mass fabrication of individual NDs the results are than transferred to Si + broad beam irradiation and cross checked by EFTEM. In this case localization will be achieved by pre-structuring the sample into narrow pillars using lithography.
This work has been funded by the European Union’s Horizon 2020 Research and Innovation Program under grant agreement No. 688072 “IONS SET”.

Keywords: HIM

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