Abstract
Abstract N-channel metal-oxide-semiconductor field effect transistors (MOSFETs) using ZrO2 gate oxide were fabricated successfully. The ZrO2 films were deposited by RF magnetron sputtering. The C-V, ID-VD and ID–VG characteristics are measured. The minimum threshold voltage was 0.32 V. The minimum subthreshold swing was 107 mV/dec. The ION/IOFF ratio is about 105 at VD=0.1 V, which indicates that the ZrO2 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 3.03x1012 cm-2-eV-1. The dielectric constant measured from a separate metal-ZrO2-silicon capacitor is 18.1. Au/ZrO2/p-Si metal-insulator-silicon (MIS) capacitors were also fabricated to characterize the electrical properties of the ZrO2 dielectric. The electrical conduction mechanisms of ZrO2 thin film as functions of temperature were studied. The temperature range is from 300 to 475 K. The leakage current density is -7.8×10-3 A/cm2 when the applied electric field is 1MV/cm and the ZrO2 thickness is 17.4 nm. At high electrical field (1.44~3.24 MV/cm) and high temperatures (425K~475K) with the Al electrode biased negative, the conduction mechanism of Al/ZrO2 interface is Schottky Emission. The intercept of fit provides an estimate of barrier height, which value is . At low electrical field (0.25~0.9 MV/cm) and high temperatures(425K~475K) with the Al electrode biased negative, the conduction mechanism of Al/ZrO2 interface is Poole-Frenkel Emission. The value of tap energy barrier is . Although the Schottky equation gives a good fit to the data, the extracted parameter such as barrier high, but thermal electrons transport thought ZrO2 thin films, thermal electrons may be suffered from trap and interface state, which is formed by oxygen vacancy and thermal stability between ZrO2 and Si, respectively. Also, the thickness of thin film would affect the behavior of Schottky emission. In insulating crystalline ZrO2, the mobility is attributed to trap limited mechanism. For above reasons, which cause electron mean-free path less than the insulator thickness. In this work, a modified Schottky emission equation is applied. At medium electrical field (1~1.96 MV/cm) and high temperatures (425K~475K) with the Al electrode biased negative, the conduction mechanism of Al/ZrO2 interface is modified Schottky Emission. The electronic mobility in ZrO2 thin films is at 425K. The SIMS and XRD analyses were made. Mean-free-path in ZrO2 bulk is between 16.2nm and 17.4nm at 425k~475K。 A comparison with MOSFETs using SiO2 and Ta2O5 gate oxides was made. The ZrO2/Si interface is generally inferior compared with that of the SiO2/Si interface. But the ZrO2/Si interface is comparable to that of the Ta2O5/Si interface. The thermodynamic stability of ZrO2 gate oxide is much better than that of Ta2O5 date oxide. In the future, MOSFETs with ZrO2 gate oxide will be a promising candidate for sub-0.1 um MOSFETs.