||For MOCVD-TiO2/Si MOS structure, oxygen vacancy and grain boundary are the main defects of polycrystalline TiO2 films. They are the main mechanisms for the leakage current. In order to improve the problems, oxygen annealing treatment is often used for filling oxygen vacancies. The electrical characteristics of as-grown MOCVD-TiO2 films can be improved. However, it is from the lattice mismatch between the TiO2 film and Si substrate. In order to release the stress, the TiO2 film will produce a lot of defects and degrade its stoichiometry. Besides, the thermal ionic emission is due to lower conduction band offset between TiO2/Si than that of SiO2/Si. These problems need further improvement.|
In order to solve the above mentioned problems, fluorinated liquid phase deposition (LPD) SiO2 deposited upon polycrystalline MOCVD-TiO2/Si. Higher barrier height (Eg = 9 eV) of fluorinated LPD-SiO2 could avoid the thermal ionic emission from lower conduction band offset of TiO2/Si. Moreover, the LPD-SiO2 film can provide fluorine (F-) from the hydrofluosilicic acid (H2SiF6) aqueous solution. Fluorine could passivate grain boundaries of poly-crystalline MOCVD-TiO2 films and interface state density (Dit) of the MOCVD-TiO2/Si interface. The main leakage current of polycrystalline MOCVD-TiO2 films could be .effective to reduce. Furthermore, nitrogen (N2) annealing was used to enhance fluorine passivation of LPD-SiO2/O2-annealed MOCVD-TiO2 films. Therefore, it can be expected that higher dielectric constant and lower leakage current density will be obtained from
LPD-SiO2/O2-annealed MOCVD-TiO2/Si MOS structure. Therefore, MOSFET with fluorinated MOCVD-TiO2 gate oxide can have lower off state leakage current, smaller subthreshold swing, higher transconductance, and higher field effect mobility.
On the other hand, LPD-SiO2/MOCVD-TiO2 film on (NH4)2Sx-treated GaAs not only can lower leakage current but can lower interface state density. The leakage current densities are 2.3×10-7 A/cm2 and 3.6×10-7A/cm2 under positive and negative electric fields at 10V, respectively. The lowest interface state density is 4.7×1011 cm-2eV-1 in the band gap. Moreover, the dielectric constant can reach 62. Therefore, LPD-SiO2/MOCVD-TiO2/(NH4)2Sx-treated GaAs structure is a high dielectric constant and low leakage current film. This structure has high potential for the further development of GaAs MOSFETs.