Carrier transport in HfO sub(2)/metal gate MOSFETs: physical insight into critical parameters

• Published in: IEEE transactions on electron devices 2006-01, Vol.53 (4)
• Main Authors: Casse, M, Thevenod, L, Guillaumot, B, Tosti, L, Martin, F, Mitard, J, Weber, O, Andrieu, F, Ernst, T, Reimbold, G, Billon, T, Mouis, M, Boulanger, F
• Format: Article
• Language: English
• Subjects: Devices; Gates; Hafnium oxide; MOSFETs; Phonons; Scattering; Silicon dioxide; Trapping
• ISSN: 0018-9383
• DOI: 10.1109/TED.2006.870888

Electron and hole mobility in HfO sub(2)/metal gate MOSFETs is deeply studied through low-temperature measurements down to 4.2 K. Original technological splits allow the decorrelation of the different scattering mechanisms. It is found that even when charge trapping is negligible, strong remote coulomb scattering (RCS) due to fixed charges or dipoles causes most of the mobility degradation. The effective charges are found to be located in the HfO sub(2) near the SiO sub(2) interface within 2 nm. Experimental results are well reproduced by RCS calculation using 710 super(13) cm super(-2) fixed charges at the HfO sub(2)/SiO sub(2) interface. We also discuss the role of remote phonon scattering in such gate stacks. Interactions with surface soft-optical phonon of HfO sub(2) are clearly evidenced for a metal gate but remain of second order. All these remote interactions are significant for an interfacial oxide thickness up to 2 nm, over which, these are negligible. Finally, the metal gate (TiN) itself induces a modified surface-roughness term that impacts the low to high effective field mobility even for the SiO sub(2) gate dielectric references.