" Electrical and physicochemical characterization of metal gate processes for work function modulation and reduction of local threshold voltage variability in 14FDSOI technologies "
Thursday, February 4, 2016 at 10:30
This Ph.D. thesis is focused on the fabrication and the electrical and physicochemical characterization of metal gates in 14 nm high-K based FDSOI MOSFET devices, manufactured at STMicroelectronics. These metal gates are composed of TiN, lanthanum and aluminum layers, deposited by RF sputtering. Test structures and a simplified integration scheme allowing C-V measurements, have been implemented in order to characterize the modulation of the effective work function of TiN metal gates with the incorporation of dopants such as lanthanum or aluminum. These additives are incorporated in a sacrificial gate-first approach. Furthermore, a new methodology based on X-ray fluorescence was proposed and validated for accurate in-line characterization of the diffusion of dopants. This methodology enables to prove that the effective dose of the species incorporated into dielectrics after diffusion annealing may be modeled as a function of the thickness of the pedestal TiN in the sacrificial gate and the annealing temperature. Moreover, the variation of the thickness of the interfacial oxide along the wafer (bevel oxide) authorizes the identification of the origin of the modulation of the effective work function, which is explained by a dipole that evolves with the effective dose of the incorporated dopant. Accordingly, empirical equations of the diffusion of dopants into the gate dielectrics and their impact on the effective work function of metal gates have been proposed to precisely modulate the threshold voltage (VTH) of the 14 nm FDSOI devices. In addition, the influence of the high-K oxide on both the diffusion of dopants and the modulation of the effective work function was highlighted. Lastly, an innovative process for metal deposition, allowing the modification of the microstructure of TiN, was developed in order to further reduce the local VTH variability in FDSOI devices.
Keywords: metal gate, work function, dopants diffusion, lanthanum, aluminum, X-Ray spectroscopy, local VTH variability, RF-PVD sputtering.
Members of the jury : Catherine DUBOURDIEU, Director of Researcher, INL Lyon : Chairman Nathalie MALBERT, Professor, IMS Université de Bordeaux: Rapporteur Brice GAUTIER, Professor, INSA de Lyon: Rapporteur Florian DOMENGIE, Engineer, STMicroelectronics: Examiner Charles LEROUX, Engineer, CEA-LETI-MINATEC: Examiner Gerard GHIBAUDO, Director of de Researcher, IMEP-LAHC: Supervisor
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Thesis preparedin the laboratory IMEP-LaHC and CEA-LETI supervised by M. Gérard GHIBAUDO .