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Etude des défauts induits par recuit laser excimère dans le silicium

Richard Monflier 1
1 LAAS-MPN - Équipe Matériaux et Procédés pour la Nanoélectronique
LAAS - Laboratoire d'analyse et d'architecture des systèmes
Abstract : The micro-electronic domain is constantly evolving in response to the continuous emerging of new application fields as well as new users' needs. The fabrication of heavily-doped regions for ultra-shallow junctions is a major issue to ensure its evolution. In this context, new doping techniques allowing to obtain ultra-shallow junctions have been developed. Nanosecond laser annealing in "melt mode" is one of these techniques. Indeed, it allows a very strong local activation (on surface and in depth) and a uniform distribution of doping. This process used in laboratory since the 1980s for the realization of solar cells offers also new technological possibilities such as the development of 3D architectures. However, degradation of several parameters sensitive to laser-induced defects were observed, such as carrier mobility and reverse current in MOS transistors or carrier lifetime in the case of photovoltaic cells. In this context, this thesis proposes a rigorous study of the defects generated by laser annealing in two parts. The first part analyses the impact of the laser annealing on the physical properties, thanks to infrared and photoluminescence spectroscopy characterizations of bare silicon samples submitted to different annealing conditions. The study highlights the formation of defects following the laser process. Their identification allowed to confirm the introduction of oxygen and carbon impurities during the annealing. From this identification, the impurities were followed in depth by secondary ion mass spectrometry allowing to reveal an increase of their concentration and diffusivity when increasing the laser energy density and/or the number of laser pulses. At high energy, the oxygen concentration profiles show the presence of an immobile peak (in agreement with the known solubility limit value in liquid silicon) which are related to silicon cavities observed by transmission electron microscopy. The origin of these impurities is also discussed and the characterization of dedicated test vehicles allowed to identify the native oxide as the source of the impurities. The objective of second part is to evaluate the impact of laser annealing on the electrical properties of silicon devices thanks to the characterization of PN and Schottky diodes. The obtained results provide an additional mean to localize the electrically active defects but also to identify them. The current-voltage characteristics of diodes systematically show an impact of the annealing on the leakage current, which is a strongly defect-sensitive parameter. More specifically, the leakage current deteriorates with increasing the laser energy. These measurements have allowed also to highlight the presence of defects at the liquid/solid interface, defects which also have a strong impact on diodes electric properties. The results are in agreement with the literature which suggests the presence of vacancies at the interface. To go further on this study, DLTS measurements have been carried out and reveal, depending on their localization (melt zone or liquid/solid interface), singular signatures suggesting several types of defects.
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Richard Monflier. Etude des défauts induits par recuit laser excimère dans le silicium. Micro et nanotechnologies/Microélectronique. Université Paul Sabatier - Toulouse III, 2019. Français. ⟨NNT : 2019TOU30067⟩. ⟨tel-02162058v2⟩

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