Electrical characterization of the hafnium oxide prepared by direct sputtering of Hf in oxygen with rapid thermal annealing

doi:10.1016/S0026-2714(03)00141-0

Microelectronics Reliability

Volume 43, Issue 8, August 2003, Pages 1289-1293

https://doi.org/10.1016/S0026-2714(03)00141-0 Get rights and content

Abstract

Electrical characterization of the hafnium oxide (HfO₂) gate dielectric films prepared by Hf sputtering in oxygen was conducted. By measuring the current–voltage (I–V) characteristics at temperature ranging from 300 to 500 K, several abnormalities in the I–V characteristics are recorded. For temperatures below 400 K, the current–voltage characteristics in high field region can be plotted with the Fowler–Nordheim law but a stronger temperature dependence was observed. Large flatband voltage shifts in the Al/HfO₂/Si capacitor were observed. The capacitance–voltage characteristics and flatband shifts are found to depend strongly on the post-deposition annealing temperature and duration. To study the reliability against high electric field, constant voltage stressing on the samples was conducted. We found that the trap energy levels are shallow and the oxide traps can be readily filled and detrapped at a low bias voltage.

Introduction

As the thickness of the silicon oxide has already been scaled down to its technological and direct tunneling (<3 nm) limit [1], [2], [3], searching for alternate gate dielectric materials with thicker physical thickness has become one of the major challenges for future 65-nm CMOS technology [2], [3]. Several high dielectric constant (high-κ) materials are being proposed to replace the silicon oxide [3]. Hafnium oxide (HfO₂) and zirconium oxide (ZrO₂), having potential to form a silicon oxide comparable interface, is considered as one of the potential candidates to replace the silicon gate oxide in future MOS devices [2], [3]. However, it was found that the ZrO₂/Si interface is thermally unstable and silicide can be formed at low temperature [4]. HfO₂/Si interface is more thermally stable and many investigations on the material properties and applications of HfO₂ have been conducted [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. However, many properties of this gate dielectric material are still unexplored. Several studies reported that the interface trap and oxide trap densities are significantly larger than the conventional thermal oxide [5], [6], [7]. Kim et al. [9] recently studied the time dependent dielectric breakdown (TDDB) of a very thin (∼4.5 nm) HfO₂ films and found that the soft and hard breakdown has different statistical distributions. Our recent X-ray photoelectron spectroscopy (XPS) study reveals that the HfO₂ film is thermally unstable during post-deposition thermal annealing [11]. Compared to the silicon oxide or silicon oxynitride [1], [2], indeed very little is known about the material and electrical properties of HfO₂ film and the HfO₂/Si interface. Hence considerable efforts are still indispensable for better understanding of the material properties, the interface structure, and the processing effects.

This work reports the thermal annealing effects, temperature-dependent current–voltage characteristics and the charge trapping properties. The details of sample preparation and electrical characterization will be given in next section and the experimental results will be presented in Section 3. Major emphases are placed on the temperature-dependent current–voltage (I–V) characteristics and the trapping and detrapping behaviors of the oxide traps based on high-frequency capacitance–voltage (C–V) measurements. The effects of post-deposition thermal annealing will also be explored.

Section snippets

Experiments

The starting materials are n-type $〈1 0 0〉$ Si wafers with a resistivity of about 20 Ω cm. The wafers were loaded into the ARC-12M chamber for Hf sputtering immediately after the standard RCA cleaning. Prior to sputtering, the chamber was vacuumed to 10⁻⁶ Torr, ionized Ar and oxygen gas (with O₂/Ar ratio of 8% or 16%) was then pumped into the chamber. The pressure is maintained at 10⁻³ Torr during the Hf sputtering and the sputtering power was 120 W. The distance between the substrate and Hf target

Results and discussion

Fig. 1 shows the Fowler–Nordheim (FN) plot of the leakage current behaviors of the Al/HfO₂/Si structure as a function of measurement temperature ranging from 325 to 500 K. The hafnium oxide was annealed in oxygen ambient at 700 °C for 10 min. It is noted that the leakage characteristics agree with the FN tunneling model for electric field higher than 2.7 MV/cm and temperature less than 400 K. However, the strong temperature dependencies in this plot cannot be explained with the weak

Conclusions

In summary, we have performed systematic experiments on the electrical characteristics of hafnium oxide (HfO₂) gate dielectric films prepared by Hf sputtering in oxygen with rapid thermal annealing. By measuring the current–voltage characteristics at temperature ranging from 300 to 500 K, several abnormal characteristics are recorded. For temperatures below 400 K, the current–voltage characteristics in the high electric field region can be plotted with the Fowler–Nordheim law but a much

Acknowledgements

The work described in this paper was supported by a UGC Competitive Earmarked Research Grant of Hong Kong (Project No: HKUST6174/01E).

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Electrical characterization of the hafnium oxide prepared by direct sputtering of Hf in oxygen with rapid thermal annealing

Abstract

Introduction

Section snippets

Experiments

Results and discussion

Conclusions

Acknowledgements

Microelectron. Reliab.

Microelectron. Reliab.

Thin Solid Films

Microelectron. Eng.

Solid-State Electron.

High-k gate dielectrics: current status and materials properties considerations

J. Appl. Phys.

Thermodynamic stability of binary oxides in contact with silicon

J. Mater. Res.

Charge trapping in ultrathin hafnium oxide

IEEE Electron Device Lett.