Interfacial Control and Modulation of Band Alignment of Atomic Layer Deposition-Derived HfO2/Si Gate Stack by Rapid Thermal Annealing
High-k gate dielectric HfO2 thin films have been deposited on Si substrates by atomic layer deposition. Postdeposition annealing temperature dependent optical properties and band alignment of HfO2/Si gate stacks are investigated via X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). XPS measurements have confirmed that annealing from 500 to 700 °C leads to the complete oxidation of the as-deposited film from the adsorption of oxygen in Si substrate and free oxygen in HfO2. However, the formation of Hf–Si–O layer has been detected after annealing at 800∼900 °C. Analysis from SE based on Cauchy mode has indicated that increases in refractive index (n) and extinction coefficient (k), with increasing annealing temperature, are observed due to the formation of higher packing density and the enhancement of scatting effect in HfO2 films. Meanwhile, red shift in band gap with the increase in annealing temperature has been observed. Additionally, the annealing temperature dependent valence band and conduction band offset relative to Si have been determined in detail.
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Document Type: Research Article
Publication date: December 1, 2014
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