| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 95 === Hafnium oxide (HfOx), niobium oxide (NbOx) and hafnium-niobium oxide (HfNbxOy) gate dielectrics were prepared on Si wafers by electron-beam evaporation from Hf and Nb sources, followed by rapid thermal annealing in N2 ambient at 500°C~800°C for 20s. Aluminum (Al) or hafnium nitride (HfN) gate electrodes were deposited on the dielectrics subsequently to form the metal-oxide-semiconductor (MOS) capacitors. Electrical properties of the different dielectrics, before and after rapid thermal annealing, are investigated with Al gate electrode. The stability of the MOS capacitors is investigated by annealing the capacitors in forming gas at 500°C with HfN electrode.
The composition of dielectric thin films was defined by X-ray photoelectron spectroscopy (XPS). The thickness of dielectric thin films was determined by high-resolution transmission electron microscopy (HRTEM). The crystal structure of thin films was identified by glacing incident angle x-ray diffraction (GIAXRD). Ellipsometry was used to measure and simulate the percentage of void in the films. For electrical properties, the C-V curves were obtained by LCR meter (HP4284), and picoampere meter/DC voltage source (HP4140B) was used to measure the leakage current.
By tuning the power of electron beam, we are able to fabricate the HfNbxOy composite oxide dielectric films of various compositions. The dielectric films are non-stoichiometric and are deficient in oxygen. HfNbxOy thin films have a thinner interlayer than HfOx and NbOx, the thinnest interlayer is less than 1 nm. The as-evaporated HfOx, NbOx, and HfNbxOy films are amorphous. After rapid thermal annealing at 500°C, the dielectric films become crystallized and the interlayer thickness increases. Low niobium content (<5%) in the HfNbxOy compositite oxide could increase the crystallization temperature to 600°C and the film also shows a less increase of interlayer thickness.
Compared to pure HfOx, the dielectrics containing niobium have less oxide trap charges but show a greater leakage current. On the electrode materials, the MOS capacitor with HfN gate electrode exhibits a smaller leakage current and reduced oxide trap charges, than the capacitor with Al electrode thus shows a good stability during thermal treatment.
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