Fabrication of advanced La-incorporated Hf-silicate gate dielectrics using physical-vapor-deposition-based in situ method and its effective work function modulation of metal/high-k stacks

Abstract

Lanthanum (La) incorporation into Hf-silicate high-permittivity (high-k) gate dielectrics was conducted using a physical-vapor-deposition (PVD)-based in situ method. PVD-grown metal Hf, La, and Hf–La alloys on base SiO2 oxides received in situ annealing to form high-quality HfLaSiO dielectrics, and subsequent deposition of metal gate electrodes was carried out to fabricate advanced metal/high-k gate stacks without breaking vacuum. The in situ method was found to precisely control La content and its depth profile and to tune the effective work function of metal/high-k stacks. Remarkable leakage current reduction of almost seven orders of magnitude compared with conventional poly-Si/SiO2 stacks and excellent interface properties comparable to an ideal SiO2/Si interface were also achieved at an equivalent oxide thickness of around 1.0 nm. Our x-ray photoelectron spectroscopy analysis revealed that, as previously suggested, effective work function modulation due to La incorporation is attributed to the interface dipole (or localized sheet charge) at the bottom high-k/SiO2 interface, which is crucially dependent on the La content at the interface. Moreover, it was found that high-temperature annealing causing interface oxide growth leads to redistribution of La atoms and forms the uppermost La-silicate layer at the metal/high-k interface by releasing the dipole moment at the bottom high-k/SiO2 interface. Based on these physical and electrical characterizations, the advantages and process guidelines for La-incorporated dielectrics were discussed in detail.

Detrimental Hf penetration into TiN gate electrode and subsequent degradation in dielectric properties of HfSiO high-k film

“…[4][5][6] Our previous study, focusing on the La-induced interface dipole in TiN/HfLaSiO/SiO 2 /Si gate stacks, showed the upward diffusion of La at temperatures above 900 C, at which point the SiO 2 underlayer thickness increased. 7 On the basis of this result, we speculated that the upward diffusion is driven by SiO 2 growth and can thus be suppressed by hampering this growth. Since a metal inserted polycrystalline silicon (poly-Si) stack (MIPS) structure can suppress SiO 2 growth during high-temperature annealing, 8,9 we considered MIPS structure as an enabler to suppress the upward diffusion.…”

“…The thickness of the deposited metal Hf was 0.5 nm and PDA treatments were carried out in a vacuum (base pressure was less than 5.0 Â 10 À4 Pa) followed by FGA. 7 Figure 3(a) shows the relationship between EOT and J g after PDA treatments (at 600, 700, 800, and 900 C) for the samples with 5-nm-and 100-nm-thick TiN gate electrodes together with their linear fit. For both TiN thicknesses, the EOT increased as annealing temperature increased.…”

Electronic Structure Characterization of La Incorporated Hf-Based High-<I>k</I> Gate Dielectrics by NEXAFS

“…The physical and electrical properties of La-incorporated Hf-based oxides, such as HfLaO and HfLaSiO, are crucially dependent on their La concentration and thermal treatment condition. Actually, one of the current authors (Arimura) toward the SiO 2 underlayers under moderate annealing condition, and the anomalous La outer-diffusion toward the high-k surfaces caused by high-temperature annealing over 900 C. 12 In addition to the threshold voltage control, the electronic structure of Hf-based oxides ought to be affected by La addition. The band-edge electronic structure of the dielectric material is important for predicting and designing the band diagrams of high-k gate stacks.…”

La Induced Passivation of High-k Bulk and Interface Defects in Polycrystalline Silicon/TiN/HfLaSiO/SiO2 Stacks

“…4) Incorporating lanthanum (La) into Hf-based oxides is effective in V th tuning for n-type metal-oxide-semiconductor field-effect transistors (nMOSFETs) due to the dipole formation at the high-k/SiO 2 interface. [6][7][8] Recent firstprinciples calculations revealed that La incorporation is beneficial for suppressing V O formation in Hf-based oxides. 9) Previously, La-incorporated high-k transistors have been demonstrated in the aim for low-V th high-performance nMOSFETs with the gate-first process.…”