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Ion beam analysis of three dimensional (3D) structures for applications in nanotechnology

Abstract : With the aim of optimizing the performances of integrated circuits (ICs), the nanotechnology industry is carrying out intense research activities on the miniaturization at the sub-22 nm scale of their main constituents: the MOS transistors. Nevertheless, the shrinking of the gate size has reached the limits that make the control of the channel problematic. One of the most promising approaches to circumvent this dilemma and thus further the miniaturization of the future technological nodes, is the development of transistors of 3D architecture (Trigate or FinFET). The elaboration of such nanostructures requires increasingly fine characterization tools precisely at a key stage of their fabrication, namely the ion implantation doping. Given the ultra-shallow implantation depths, the medium energy ion scattering (MEIS) analysis technique is suitable for quantifying the implants and evaluating the doping conformity thanks to its good depth resolution (0.25 nm). However, the dimensions of the beam (0.5×1 mm2) being by far larger than those of the patterns, we had to develop an analysis protocol dedicated to such architectures. The samples studied in the framework of this thesis are considered as model systems. They are constituted of 3D silicon (Si) Fin – shaped line gratings, etched on the 300 mm wafers of silicon on insulator (SOI) types by using the electron beam (e-beam) lithography. The doping has been carried out at an energy of 3 keV by using the conventional (or beam line) and plasma immersion ion implantation (PIII) methods.The analyses s of the MEIS spectra of the dopants implanted into each part of the patterns were possible thanks to the 3D Monte-Carlo simulations performed with the PowerMEIS software. We have thus developed a new method suitable for the characterization of the 3D doping. The measurements have shown that, contrarily to the PIII method, the dose implanted by the conventional method is as targeted. However, the distribution of the dopants inserted within the nanostructures by using the two doping methods is not uniform. In the PIII implanted samples, a large dopants' focusing at the tops of the patterns and low sidewalls' doping have been observed. This is less marked in the one implanted by the conventional method. By correlating the Transmission Electron Microscopy (TEM), synchrotron x – ray analyses and MEIS, we have also determined the dimensions of the implanted and crystal areas of the line gratings.The exploitation of the MEIS technique in channeling mode has permitted the full assessment of the impacts of the implantation in the non-etched layers. The investigations of the crystal qualities in the non-implanted areas were carried out with the same technique. The results show that the temperature conditions have a considerable influence on the defects and lattice deformations. The origin of the anomalies in the samples has thus been identified by correlating the MEIS and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) measurements.
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Lucien Penlap Woguia. Ion beam analysis of three dimensional (3D) structures for applications in nanotechnology. Materials Science [cond-mat.mtrl-sci]. Université Grenoble Alpes, 2019. English. ⟨NNT : 2019GREAY015⟩. ⟨tel-02443991⟩

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