| Summary: | 博士 === 國立交通大學 === 電子工程系 === 91 === According to the continuous scaling of device, the thickness of gate oxide has to be reduced. However, the high leakage current degrades the performance of transistors and enlarges the power consumption of the devices. Therefore, the replacement of conventional thermal oxide with high k dielectrics is inevitable. Although utilizing high k dielectrics reduced the gate leakage current effectively, there are still some issues that we have to overcome. We have developed a approach to deposit high k dielectrics. We deposited the ultra thin metal film using PVD followed by oxidation and annealing. Using this method, we can deposit Al2O3 under the other high k dielectrics. This Al2O3 layer can not only prevent from the formation of interface oxide, but also provide Al-doping into high k dielectrics to reduce the high temperature crystallization. In this study, we deposited both Al2O3 as well as AlTiOx on Si substrate and fabricate the capacitors suitable for RF measurement. To investigate the characteristics of them used as gate dielectric at RF region, we measured the S-parameters and the noise figure. Using the simulation software, the capacitance of the device at different frequencies was extracted. The result indicates that Al2O3 and AlTiOx having some thickness ratio of Al to Ti, exhibits the similar capacitance reduction rate with SiO2. Form the point of view of noise figure, Al2O3 exhibits the similar noise figure with SiO2, but AlTiOx shows the higher noise figure than others. After constant voltage stress, the increase of leakage current tends to increase the noise figure. We can deduce the mechanism of noise generation. Besides, we also fabricated RF capacitors using Al2O3 and AlTiOx. The measurement results suggest that capacitors using AlTiOx exhibits higher capacitance density, but this merit is compensated by the capacitance reduction at high frequency. However, this issue can be overcome by tuning the thickness ratio of Al2O3 and TiO2. Therefore, using this approach, we can fabricate the high k dielectric that is suitable in RF application. More important, this approach is simple and fully compatible with current VLSI technology.
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