Hafnium oxide (HfO 2 ) gate dielectric film was prepared by Hf sputtering in oxygen, and the thermal instability of HfO 2 was investigated by rapid thermal annealing ͑RTA͒ in nitrogen. X-ray photoelectron spectroscopy study reveals that the HfO 2 film is thermally unstable at postmetallization annealing temperatures (Ͼ500°C). The HfO 2 film decomposes and some oxygen atoms are released upon the RTA in nitrogen. In addition, the current-voltage characteristics of the Al/HfO 2 /Si capacitor are also highly unstable at temperatures higher than 300 K. These observations suggest that although HfO 2 has a much higher dielectric constant, it may not be suitable for the gate dielectric application because the postdeposition thermal treatment deteriorates both the physical and the electrical properties of the HfO 2 film.

Articles you may be interested inTemperature-dependent structural stability and optical properties of ultrathin Hf-Al-O films grown by facingtarget reactive sputtering Chemical states and electrical properties of a high-k metal oxide/silicon interface with oxygen-gettering titaniummetal-overlayer Appl.The interface properties of the hafnium gate oxide films prepared by direct sputtering of hafnium in oxygen with rapid thermal annealing have been investigated in detail. X-ray photoelectron spectroscopy reveals that the interface silicate layer is a random mixture of Hf-O, Si-O, Hf-Si, and excess Hf and Si atoms. The contributions of these bonds to the composition of silicate layer are governed by the Si/Hf ratio. At low Si/Hf ratio ͑Ͻ2͒, the silicate layer is a mixture of SiO 4 and HfO 4 phases. At higher Si/Hf ratio ͑2-5͒, the contribution of the HfO 4 phase decreases and Hf-Si ͑silicide͒ bonds become important. At very high Si/Hf ratio ͑Ͼ9͒ and close to the substrate, Hf-Si dominates and the high strain Hf-Si bonds govern the electrical properties of the interface. These results explain the observed high interface trap density at the HfO 2 /Si interface and the soft breakdown behavior which is different from the silicon oxide film.

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