Hydrogen induced positive charge in Hf-based dielectrics

Hafnium dioxide (HfO 2) attracts attention because of its high dielectric constant, wide band gap, and also since it can be quite effortlessly grown on the surface of a silicon substrate. In this work, dense ceramics of hafnium oxide in the monoclinic phase was synthesised from a liquid precursor of hafnium tri-methyl-tetra-oxide (Hf [O(CH 3) 3 ] 4) and sintered by conventional techniques. The electrical properties of the sample were studied by broadband dielectric spectroscopy over a wide range of frequencies (10 − 1-10 6 Hz) and temperature range (300-670 K). The temperature and frequency dependencies of the dielectric response exemplify high stability of the material in the investigated temperature range. The dielectric constant of conventionally sintered ceramics at room temperature is ~13. The frequency dispersion of ceramics was revealed and analysed over the entire investigated temperature range. It is shown that the main contribution to the response is made by lowfrequency charge polarisation. DC conductivity of HfO 2 has a thermally activated character with an activation energy of 1.2 eV in the temperature range below 600 K and 0.9 eV above 600 K. The conductivity is determined by oxygen vacancies.

2004

Applied Physics Letters, 2004

High-resolution electron microscopy, electron energy-loss spectroscopy, and first-principles theory are used to investigate the composition and electronic structure of HfO2 dielectric layers deposited directly onto Si. A thin, nonstoichiometric, but Hf-free SiO2 layer forms between the HfO2 dielectric and the substrate, consistent with one-dimensional spinodal decomposition. Rapid thermal annealing crystallizes the HfO2, and the resulting grain boundaries within the HfO2 are found to be O-depleted, with localized states within the bandgap. These localized states are thought to act as significant leakage pathways, and may be responsible for Fermi-level pinning at the dielectric/contact interface.

Microelectronic Engineering, 2009

We have investigated electrical stress-induced positive charge buildup in a hafnium aluminate (HfAlO)/ silicon dioxide (SiO 2 ) dielectric stack (equivalent oxide thickness = 2.63 nm) in metal-oxide-semiconductor (MOS) capacitor structures with negative bias on the TaN gate. Various mechanisms of positive charge generation in the dielectric have been theoretically studied. Although, anode hole injection (AHI) and valence band hole tunneling are energetically favorable in the stress voltage range studied, the measurement results can be best explained by the dispersive proton transport model.

Applied Physics Letters, 2005

The atomic structure of HfSiO and HfSiON was investigated before and after thermal annealing using x-ray diffraction and x-ray absorption spectroscopy. In HfSiO, the Hf atoms are arranged in a monoclinic HfO 2 structure with Hf as second nearest neighbors, while Si is in a SiO 2 environment. Thermal annealing induces crystallization of HfSiO with subtle changes in Hf-Hf distances. In the case of HfSiON, a stable structure is observed around the Hf atoms, which remains unaffected after annealing. Nitrogen is present in the first coordination shell of the Hf atoms, with Si in a SiON environment.

Applied Physics Letters, 2004

High-resolution electron microscopy, electron energy-loss spectroscopy, and first-principles theory are used to investigate the composition and electronic structure of HfO 2 dielectric layers deposited directly onto Si. A thin, nonstoichiometric, but Hf-free SiO 2 layer forms between the HfO 2 dielectric and the substrate, consistent with one-dimensional spinodal decomposition. Rapid thermal annealing crystallizes the HfO 2 , and the resulting grain boundaries within the HfO 2 are found to be O-depleted, with localized states within the bandgap. These localized states are thought to act as significant leakage pathways, and may be responsible for Fermi-level pinning at the dielectric/ contact interface.

IEEE Electron Device Letters, 2000

Effects of nitrogen incorporation on suppression of electron charge traps in Hf-based high-κ gate dielectrics have been studied by first-principles calculations, focusing on interactions between N atoms and electrons trapped at oxygen vacancies (V O 's). Our total energy calculations revealed that the formation energy of a doubly occupied state of V O is significantly increased in HfO x N y compared to that in HfO 2 . This clearly indicates that the electron charge traps at V O 's are considerably suppressed by N incorporation.

Applied Physics Letters, 2002

A stoichiometric, uniform, and amorphous hafnium oxide thin film is deposited by an atomic layer deposition process. The as-deposited hafnium oxide films showed superior electrical properties compared to zirconium oxides, including a dielectric constant of 23, a flatband voltage shift of ϩ0.3 V, a hysteresis of 25 mV, an interfacial trap density of 1.8ϫ10 11 cm Ϫ2 eV Ϫ1 , and a leakage current density several orders of magnitude lower than SiO 2 at an equivalent oxide thickness of 9.3 Å, suitable for metal-oxide-semiconductor device applications. The thermal stability of hafnium oxide on silicon was determined to be better than that of zirconium oxide. Post-deposition annealing in oxygen and ammonia further improved the thermal stability of HfO 2 to 1000 and 1100°C, respectively.

Thin Solid Films, 2005

In this study, the hump in the capacitance-voltage (C-V) curves, variation of leakage current, interfacial layer increase, and electron trapping in non-surface treated hafnium oxide (HfO 2) samples were observed and investigated. From the results of the investigation, it was found that both rapid thermal oxidation and NH 3 surface treatments improved the C-V curves. In addition, it was observed that samples treated with ammonia exhibited a lower leakage current when compared with the others. From the results of the dielectric leakage current study, a severe electron trapping effect was exhibited under higher electric field stress. Finally, the conduction mechanism in the HfO 2 thin film was dominated by Frenkel-Poole emission in a high electric field.

2011

Bias temperature instability of metal-oxide-semiconductor field effect transistors (MOSFETs) with various concentrations of La incorporation in Hf-based dielectrics was characterized by varying the magnitude and polarity of the stress biases. Contrasting dependences of charge trapping on the magnitude of the stress biases are shown by changing the bias polarity. A model based on the distortion of asymmetric energy band diagrams and La-induced interface dipoles is suggested to explain this behaviour. Change of gate leakage currents according to La-incorporation, magnitude, and polarity of bias stresses supports the validity of the model. V