Abstract
A comprehensive study of the electrical and physical characteristics of Lanthanum Aluminate (LaAlO3) high-dielectric-constant gate oxides for advanced CMOS devices was performed. The most distinctive feature of LaAlO3 as compared with Hf-based high-k materials is the thermal stability at the interface with Si, which suppresses the formation of a low-permittivity Si oxide interfacial layer. Careful selection of the film deposition conditions has enabled successful deposition of an LaAlO3 gate dielectric film with an equivalent oxide thickness (EOT) of 0.31 nm. Direct contact with Si has been revealed to cause significant tensile strain to the Si in the interface region. The high stability of the effective work function with respect to the annealing conditions has been demonstrated through comparison with Hf-based dielectrics. It has also been shown that the effective work function can be tuned over a wide range by controlling the La/(La + Al) atomic ratio. In addition, gate-first n-MOSFETs with ultrathin EOT that use sulfur-implanted Schottky source/drain technology have been fabricated using a low-temperature process.
Highlights
High-k gate dielectrics have been widely researched over the last decade and are currently being used in practical devices [1]
The stability of the effective work functions for p-metals on La-based high-k materials is studied in detail for various annealing ambients and gate dielectric structures, because it has been widely reported that φeff for p-metals on Hf-based high-k materials depends strongly on the annealing ambient [26,27,28]
The reported φeff instability of Hf-based high-k materials, in which oxygen vacancies probably form as a result of FGA or high-temperature annealing at around 1000 °C, may have the same mechanism as that observed in the Pt/LHO/SiO2/Si stack in this study
Summary
High-k gate dielectrics have been widely researched over the last decade and are currently being used in practical devices [1]. In the as-deposited state, no peak derived from an interfacial layer could be observed on either film, indicating that a direct LAO/Si structure was achieved, irrespective of the deposition temperature. In the as-deposited RT-LAO film, an asymmetrical spectrum was obtained, indicating that multiple bonding states of oxygen exist in the film This inhomogeneity in the bonding in the RT-LAO film is thought to be closely related to interfacial layer formation during vacuum annealing. The spectra for mass (H2O) (not shown) were similar to those for mass (H2O) These results suggest that RT-LAO contains a large amount of the OH group and H2O, which could diffuse into the film during annealing and cause interfacial layer formation. The HT deposition process can suppress the incorporation of these oxygen-related components during deposition and inhibit subsequent interfacial layer formation during annealing
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