| Summary: | 碩士 === 國立清華大學 === 電子工程研究所 === 90 === N-channel metal-oxide-semiconductor field effect transistors (MOSFETs) using HfO2 gate oxide were fabricated successfully. The HfO2 films were deposited by RF magnetron sputtering. The C-V, ID-VD and ID—VG characteristics are measured. The minimum threshold voltage was 0.67 V. The minimum subthreshold swing was 78.5 mV/dec. The ION/IOFF ratio is about 106 at VD=0.05 V, which indicates that the HfO2 MOSFETs have good current switch capability. Since St=2.3(kT/q)[1+(CD+Cit)/Cox], the interface trapped charge density Dit is extracted to be about 3.16x1012 cm-2-eV-1. The dielectric constant measured from a separate metal-HfO2-silicon capacitor is 18.9.
Au/HfO2/p-Si metal-insulator-silicon (MIS) capacitors were also fabricated to characterize the electrical properties of the HfO2 dielectric. The electrical conduction mechanisms of HfO2 thin film as functions of temperature were studied. The temperature range is from 300 to 425 K. The leakage current density is -6.5×10-3A/cm2 when the applied voltage is -1 V and the HfO2 thickness is 133.4 nm. At low electrical field (<0.8 MV/cm) and with the Au electrode biased negative, the conduction mechanism of Au/HfO2 interface is Schottky Emission. The SIMS, XRD and SEM analyses were made.
The interface trapped charge density, the surface recombination velocity, and the minority carrier lifetime in the field-induced depletion region measured from gated diodes were 5.3x1013 cm-2-eV-1, 4310 cm/s, and 2.2x10-8 sec, respectively. A comparison with MOSFETs using SiO2 and Ta2O5 gate oxides was made. The HfO2/Si interface is generally inferior compared with that of the SiO2/Si interface. But the HfO2/Si interface is comparable to that of the Ta2O5/Si interface. The thermodynamic stability of HfO2 gate oxide is much better than that of Ta2O5 date oxide. In the future, MOSFETs with HfO2 gate oxide will be a promising candidate for sub-0.1 um MOSFETs.
|
|---|
