超薄高介電係數介電層金氧半元件之特性分析及可靠度與靈敏度改善

Abstract

With the aggressive downscaling of MOS devices in semiconductor industry, the high-k gate dielectrics continuously play significant roles to achieve small equivalent oxide thickness for high-performance logic technology. The low manufacturing cost and low-temperature process of high-k dielectrics are also of practical interests for display and solar cell industry. In this dissertation, the Al2O3 MOS devices using room-temperature sputtering followed HNO3 compensation technique were demonstrated. After HNO3 compensation, the surface roughness, interface trap density, flatband voltage, and leakage current would also be effectively improved. The better reliability performance was also observed in dielectric breakdown tests and ten-year lifetime projections. Moreover, the positive bias current of Al2O3 MOS devices without HNO3 compensation showed the irregular temperature response at temperature above 70 ℃, which is corresponding to Frenkel-Poole emission. In contrast, the generation-recombination current is the dominant component for the Al2O3 MOS devices with HNO3 compensation. Using the temperature-sensitive current characteristics, we successfully demonstrated the Al2O3 MOS tunneling temperature sensors with enhanced temperature sensitivity and improved power consumption in comparison with SiO2 and HfO2 sensors. Subsequently, the electrical nonuniformity of ultrathin SiO2 and HfO2 gate dielectrics was investigated. The effective uniform area ratio regarded as an indication of gate oxide quality can be extracted from the deep depletion of C-V characteristics. In our cases, the effective uniform area ratio increases with SiO2 thickness, whereas decreases with increasing equivalent oxide thickness of HfO2, which was also reconfirmed by the same trend of leakage current fluctuations and the constant field stress measurements. Furthermore, a particular edge-dependent inversion current behavior resulting from edge fringing effect was observed for MOS tunneling diodes. The inversion current would increase with increasing tooth spacing for comb-shaped MOS tunneling diodes. The results suggested that the current conduction would be controlled by the electron diffusion current between the teeth and hole tunneling current affected by Schottky barrier height lowering. Finally, the photosensitivity can be improved by reducing SiO2 thickness and selecting smaller tooth spacing for SiO2 comb-shaped MOS tunneling photodiodes. In addition, the HfO2 photodiodes demonstrated high and steady photosensitivity owing to the current conduction dominated by electron only and smaller conduction band offset. In appendix of this dissertation, the electrical transport and photoconductive characteristics of CdTe nanowire transistors were investigated, which cooperated with the NANI group in University of Southern California. The Sb doped CdTe nanowire transistors exhibited p-type conductivity. Two acceptor levels existing in energy bandgap of CdTe nanowire were found via low-temperature electrical measurements, which is exactly in agreement with the photoluminescence measurement results. In addition, the Sb doped CdTe nanowire transistors demonstrated significant photoresponse to visible-near-infrared irradiation.