Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis The Effects of Prior Nitridation Process of Silicon Surface and Different Metal Gates on the Capacitance Voltage Characteristics of Metal-Ta2o5 Mos Capacitor(Izmir Institute of Technology, 2007) Özben, Eylem Durğun; Güneş, Mehmet; Güneş, Mehmet; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyAccording to the 2004 International Technology Roadmap of Semiconductor (ITRS), for sub-micron technology, an equivalent oxide thickness (EOT) less than 1 nm is required. However, for such thickness levels, the native oxide SiO2 is unacceptable since it does not posses its inherited physical properties and results in high leakage current density resulting in reduced device performance. The replacement of SiO2 with high dielectric constant material (high-k) may eliminate such problems since it will allow the usage of thicker dielectric material. The leakage current will be reduced while maintaining the same levels of inversion charge. In this study, the electrical properties of metal-Ta2O5-Si MOS capacitor were investigated for devices prepared with different conditions. A prior nitridation process of silicon surface in N2O and NH3 gas before Ta2O5 was carried out to improve interface quality. In addition, different metal gates formed on the Ta2O5 oxide layer were also used in order to see the effects of top oxide-metal gate on the electrical properties of MOS capacitors. The metal gates used are Al, TiN and W. High frequency (1MHz) Capacitance-Voltage Spectroscopy was used to understand the effects of prior nitridation process and metal gates on the Ta2O5 high-k oxide properties. From the analysis of high frequency C-V curves, oxide capacitance, dielectric constant, EOT, leakage current density, conductance, flat band voltage VFB shift, mobile charge density, effective oxide charge and interface trap density Dit were obtained and compared with those of reference samples. Reference sample -1 has native oxide SiO2 and Al metal gate and Reference sample-2 has Ta2O5 oxide layer with unnitrided silicon surface. It has been found that, the replacement of SiO2 gate oxide with Ta2O5 oxide layer results in an increase in dielectric constant by several factors and using nitridation process prior to Ta2O5 oxide layer improves the interface properties. Many promising results were obtained for samples with W metal gates and nitrided silicon surface prior to formation of Ta2O5 oxide layer. It is potentially applicable to future MOS devices.Master Thesis Capacitance-voltage spectroscopy in metal-tantalum pentoxide (Ta-O)-silicon mos capacitors(Izmir Institute of Technology, 2005) Özdağ, Pınar; Güneş, Mehmet; Güneş, Mehmet; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe electronic properties of Al-Ta2O5-Si MOS capacitors with oxide layers prepared by RF magnetron sputtering with or without a prior nitridation process in N2O or NH3 gas environments at temperature ranges between 700 °C to 850 °C were investigated using Capacitance-Voltage (C-V) Spectroscopy to determine the quality of oxide layer and oxide-silicon interface. The theoretical ideal capacitance-voltage calculations were compared with the experimental capacitance-voltage results in order to evaluate effective oxide charges, Qeff , present inside Ta2O5 insulating layer and density of interface trap states, Dit, present at the Ta2O5-Si interface. In addition,dielectric constant, doping concentration, flat band voltage values were determined by using the experimental data. Finally, the effects of deposition conditions on Ta2O5 MOS capacitors were compared by using a reference sample of a MOS capacitor with native oxide SiO2. It has been found that dielectric constant value up to 12 have been reached for Ta2O5 insulating layers which increases the capacitance value several times than that of MOS capacitor with native oxide SiO2. The density of interface trap states, Dit, for unnitrided Ta2O5 MOS capacitors, values around 1.6x1012 cm-2 eV-1 have been detected which is much higher than that of MOS capacitor with native oxide SiO2. However, prior nitridation process enhances the interface properties and Dit values down to 2-5x1011 cm-2 eV-1 have been reached for the nitrided samples which is in the limits for MOS capacitors with high quality insulating layers. In addition, the effective oxide charges, Qeff, for unnitrided samples, values as high as 3x1012 cm-2 were detected. Even though nitridation process enhances interface properties, the effective oxide charges are found to be higher for nitrided samples. Best electrical and interface properties are obtained by nitridation process at 800 °C in N2O and NH3. It can be inferred that samples nitrided in N2O gas at 800 °C improves the dielectric constant above the level of SiO2 and decreases both Qeff and Dit levels to that of native oxide SiO2. These results show that a prior nitridation of p-silicon surface is a promising approach to improve both oxide and interface properties of Al-Ta2O5-Si MOS devices. However, further investigation is necessary to understand the nature of these oxide charges and interface properties of MOS devices with high dielectric constant oxide layers before integration into large scale fabrication.