| Summary: | 碩士 === 國立暨南國際大學 === 電機工程學系 === 100 === In this thesis, we studied the reliability of HfO2 film under static stress and dynamic stress. The research topics are: (1) Effects of the surface pre-treatment； (2) Effects of the gate-electrode area.
First, we used atomic layer deposition (ALD) HfO2 film with different deposition thicknesses and various surface pre-treatments to measure the electrical properties and reliability of the metal-oxide-semiconductor capacitor (MOSC). Experimental results indicate that HfO2 film with ozone (O3) pre-treatment has best performance in the leakage current, flat-band voltage, hysteresis, and charge trapping. On the other hand, the HfO2 films without RCA standard clean present the worst electrical characteristics. For the reliability performance, irrespective of the deposition thickness, the HfO2 film with O3 pre-treatment has better breakdown field and lifetime due to a lower generation of interface traps during stress as compared with other surface pre-treatments. In addition, the improvement in lifetime of the HfO2 capacitors with various pre-treatments under dynamic stress is different. The HfO2 capacitor with O3 pre-treatment under dynamic stress has the best improvement of lifetime. It can improve the lifetime by 6.65 times. While the HfO2 capacitor without RCA standard clean only improve the lifetime by 5.97 times. This difference is due to the less accumulated charges of the HfO2 capacitors with O3 pre-treatment during dynamic stress.
Second, we compared the electrical properties and reliability of HfO2 capacitors with different gate-electrode areas. Experimental results indicate that the HfO2 capacitor with a larger area has more charge and traps during stress and results in the worst electrical performance. However, the HfO2 capacitor with a larger area under dynamic stress behaves the better electrical improvement because the effect of charge detrapping becomes effective. Compared to static stress, the HfO2 capacitor with a larger area under dynamic stress can improve the leakage current by 2.14 times and this improvement is reduced as the gate area decreases. For the reliability performance, as the area of HfO2 capacitor decreases, the phenomenon of soft breakdown is increased and the breakdown time increases. This is due to the soft breakdown represents the charge trapping-detrapping in the gate dielectrics. Additionally, a higher frequency and lower duty cycle in the dynamic stress resulted in a longer lifetime enhancement. Irrespective of the static and dynamic stress, the breakdown distributions of HfO2 capacitors with various areas can be merged to a single Weilbull plot, suggesting that the dielectric breakdown is intrinsic for both cases. Additionally, increasing the stress time and voltage of the opposite polarity in the dynamic stress enhanced the dielectric breakdown lifetimes. We also found that an increase in the dielectric breakdown time is observed as the stress at the opposite polarity above 10-3 s, indicating that there is a critical time for enhancement in charge detrapping.
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