| Summary: | 碩士 === 國立臺灣大學 === 電子工程學研究所 === 104 === In this thesis, we use Oxide MBE system to deposit oxide layers (HfO2) on InAs substrates to fabricate the Metal-oxide-semiconductor capacitor (MOSCAP). Hafnium dioxide was grown by hafnium metal source with oxygen plasma. Before depositing high κ dielectric layers, we used hydrogen plasma to remove the native oxide and passivate the substrates, which effectively reduced C-V stretch-out and suppressed the gate leakage current density, which was about 1x10-6 A/cm2 at Vg = -1 V. We used X-ray photoelectron spectroscopy (XPS) to discuss interface properties with and without hydrogen plasma pretreatment. With hydrogen plasma treatment, the XPS spectra show that the treatment can effectively reduce As-related oxides. And then, we used Hf (4f) spectrum and O (1s) spectrum to calculate the ratio of Hf and O, which is 1: 1.95. It is very close to prefect ratio, which can justify quality of oxide layers. Without hydrogen plasma treatment, the data of XPS showed the signal of native oxides distinctly. The gate leakage current density was about 1x10-4 A/ cm2 at Vg = -1 V, two order higher than that of with hydrogen plasma pretreatment. We used Hf (4f) spectrum and O (1s) spectrum to calculate the ratio of Hf and O is 1: 1.79, some portion of oxygen combined with As- and In- is not close to perfect ratio. The results show that with post metallization annealing improve device performances exhibiting larger C-V modulation, unpinned Fermi-level. By bidirectional C-V sweep, we calculated hysteresis voltage difference(ΔV), which used to determine whether oxide layer traps increasing or decreasing. The problems of border traps due to accumulation frequency dispersion will be discussed later.
In this thesis, we also use deflector bias when growing HfO2. Using the deflector can effectively reduce ionic species and get high quality oxide layer. With deflector bias, we get larger capacitances and thinner oxide layers. The gate leakage current density is about 4x10-6 A/ cm2 at Vg = -1 V. With deflector bias at 750 V, the samples showed hysteresis voltage difference is 114 mV before Post Metallization Anealing (PMA) and 57 mV after PMA. Without deflector bias, the samples showed hysteresis voltage difference is 205 mV before PMA and 90 mV after PMA. With deflector bias, it can effectively improve device performances. Border trap density and accumulation frequency dispersion are also effectively reduced by post metallization annealing process.
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