PhD thesis (Université de Toulouse, spécialité Nanophysique) entitled:
"Compréhension de la modulation du travail de sortie de métaux de grilles pour l'intégration à bas budget thermique du CMOS 20-14 nm"
The thesis will be held Friday, November 21 2:00 p.m. in CNRS Grenoble Bâtiment administratif - salle de séminaires - Tour A - 2e étage 25, rue des Martyrs – BP 166, 38042 GRENOBLE CEDEX 9
Mme Catherine DUBOURDIEU - DR CNRS - INL - Lyon - Rapporteur
M. Christophe VALLEE - Professeur UJF - LTM - Grenoble - Rapporteur
Mme Elisabeth BLANQUET DR CNRS - SIMAP - Grenoble - Examinateur
M. Frédéric MORANCHO Professeur UPS - LAAS - Toulouse - Examinateur
Mme Sylvie SCHAMM-CHARDON - DR CNRS - CEMES - Toulouse - Directeur de thèse
M. Remy GASSILLOUD - Docteur-Ingénieur - CEA-Leti - Encadrant de thèse
M. Pierre CAUBET - Ingénieur - STMicroelectronics - Co-encadrant
M. Daniel BENSAHEL - Conseiller Scientifique - CNRS-INSIS - Co-encadrant
Since the 45nm CMOS technological node, the microelectronics industry replaced the historical SiO2/polysilicon gate stack by the high permittivity oxide HfO2/metal couple. However, because of the use of integration schemes with a high thermal budget, the uncontrolled interdiffusion of elements in these new gate stacks is not favorable for obtaining the electrical parameters required by the ITRS (International Technology Roadmap for Semiconductors) roadmap, in particular the effective work function (EWF) and the equivalent oxide thickness (EOT). One solution to overcome this difficulty is to use an integration scheme with a lower thermal budget (≤400°C).
In the frame of this approach, the aim of this thesis work was to propose and study metals compatible for the sub-20nm complementary MOS (CMOS) technological nodes with an adapted subnanometric EOT and EWFs compatible with a nMOS (4.1-4.4 eV) and pMOS (5.1-4.8 eV) co-integration scheme. For this, we decided to determine the physico-chemical mechanisms responsible for the EWF and EOT values of chosen gate stacks. We performed a systematic study of the elementary distributions and the chemical bonding within the nanometric sized stacks investigating HRTEM/EDX nanoanalyses and mesocopic methods like XPS (ToF-SIMS). The interpretation of the results based on thermodynamics was correlated to the electrical measurements of the EWF and EOT parameters, which allowed finding innovative solutions.
The TiAlNx electrode directly deposited on HfO2 appeared as one potential solution. By modulating the nitrogen content in the metal, we demonstrated a subnanometric EOT and for the first time a 0.8eV shift between a TiAlNx<1 electrode with a low N content (4.2 eV) and a TiAlNx>1 electrode with a high N content (5.0 eV). These results were obtained after understanding how nitrogen and oxygen are redistributed within the stacks. In particular, their solid solubility, high in Ti and nearly zero in Al, is used to justify the remote scavenging of oxygen from the interfacial silicon oxide (EOT) and the formation of a TiAlNx metal with a TiN character (high EWF) or a Ti-rich character (low EWF).
Even the dual character of TiAlNx was demonstrated, it is not stable for further integrations with post-annealing up to 500°C. We proposed thus to consider two simpler metallic systems obtained by alloying two single metals with complementary properties. They are both based on nickel, a high WF metal stable regarding the oxygen of the interfacial oxide. The TaNix alloy gives a pMOS character to the stack, complementary to the nMOS character of HfO2/Ta (4,75-4,35eV). The NiTix alloy gives an nMOS character to the stack, complementary to the pMOS character of HfO2/Ni (4,2-5,0eV). These alloys appear promising for current MOSFET technologies.