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The Ion Beam Preparation and Characterization of Hafnium-based Gate Dielectric Doped Tantalum

Author: YuTao
Tutor: ZhuGeLanJian；WuXueMei
School: Suzhou University
Course: Materials Physics and Chemistry
Keywords: dual ion beam Ta2O5 thin film HfTaO-based capacitor structure electrical characteristics
CLC: TB383.2
Type: Master's thesis
Year: 2011
Downloads: 13
Quote: 1
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Abstract


In order to solve a remarkable increase in tunneling leakage current through the ultra-thin gate dielectrics, materials with a high dielectric constant （high k） have been introduced as gate dielectrics alternative to conventional SiO2, Hf-based high-k materials have been drawn attention for a long time because of its high dielectric constant and crystallization temperature, excellent interfacial properties and thermal stabilities, low frequency dispersion and leakage current density.In this letter, Ta2O5 and HfTaO thin films were deposited on p-type Si substrate with a resistively of 38 cm using an dual ion beam sputtering deposition technique （DIBSD） at a base pressure of 5×10-4 Pa and work pressure of 3.2×10-2 Pa. A special focus of the study is to reveal the association between the structure, dielectric properties and the various ion beam energy of the assisted ion source as well as the content of doping elements. Besides, influence of the different metal electrodes （Ag、Au、Pt） on the leakage currents, capacity, reliable characteristics and conduction mechanism of HfTaO-based capacitor have been studied.The experimental results indicated that: （a） the Ta2O5 film prepared under 200eV have the smallest surface roughness and excellent interfacial characteristics. C-V and I-V characteristic curves indicate that the Ta2O5 MOS has the minimum value of flat voltage offset, density of oxides charges and leakage current. Eventually we found the appropriate assisted source energy can effectively improve the film’s growth mechanism and makes the film growth type from the island into a layered, which will improve the uniformity of crystalline grain and the film’s roughness and compactness. （b）We significantly improved the physical and electrical characteristics of HfTaO gate dielectrics by incorporating Ta into HfO2 films. Especially, Hf0.54Ta0.46O sample exhibited the highest k value（22） and crystallization temperature of 900℃, the smallest flat-band voltage, oxide-charge density and leakage current. （c） It is proved that the Pt-electrode capacitor still has the smallest leakage current value at a high electric field even though its Eot is lower than that of the Ag, Au-electroded. The result is mainly due to Pt with a high enough work functionφms（Pt）=5.65eV. In a word, it is thus proposed that Pt electrode has a strong potential for future nano MOS devices.

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