Study On The Leakage Current Transport Mechanism And The Energy Band Offsets Of The Amrorphous La₂O₃ Films

Recently, with continuous scaling down of the feature size of complementary metal-oxide-semiconductor(CMOS) devices, the traditional silicon oxide gate dielectric approaches its fundamental limit. In order to reduce the leakage current and maintain the capacitance, dielectrics with high dielectric constants(high-k) have to be investigated to replace traditional SiO2 gate dielectrics. Rare earth(RE) metal oxide films, such as Er2O3, Tm2O3 and Y2O3, have been actively investigated as the secondary generation high-k gate dielectric material for future CMOS transistors devices because of high dielectric constants, wide band gaps and thermal stability with Si. In particular, La2O3 is considered as a promising high-k candidate due to its higher dielectric constant(~30) and lower bulk trap density. Although there are some reports on the determination of the band gap of La2O3, the valence-band offset(VBO) and conduction-band offset(CBO) of La2O3 to Si substrates have been discussed rarely. To be determined that La2O3 is a promising candidate in the field of microelectronics as high-k material, the band offsets value and symmetry of the La2O3 films to different substrates is very important factors. This paper will study on the leakage current transport mechanism and the energy band offsets of the amorphous La2O3 on Si substrates. In addition, there are discussed with applications of Raman spectroscopy method.La2O3 films were deposited on Si substrates(100) by radio frequency magnetron sputtering with a La2O3 target at room temperature. X-ray diffraction(XRD) shows that the films are amorphous structure. Auger electron spectroscope(AES) was employed to investigate the composition of the films. The results show that the La2O3 films are stoichiometric. Atomic Force Microscopy(AFM) was used to observe the surface of La2O3 films.Based on the I-V measurement experimental results of leakage current characteristics at 298 K and Fowler-Nordheim tunneling characteristics at 77 K, we have extracted the energy band diagrams and current transport mechanisms for metal/La2O3/Si structures. The characterization reveals that the dominant conduction mechanisms in the region of low field under substrate injection and gate injection are Schottky emission and Frenkel-Poole conduction, respectively. The barrier height of La2O3/Si, Pt/La2O3, Al/La2O3 are 1.78±0.1 eV, 2.85±0.1 eV and 1.7±0.1 eV, respectively. The electron effective mass in La2O3 is 0.2 m0, where m0 is the free electron mass.The band gap of the La2O3 films was analyzed by X-ray photoelectron spectroscopy(XPS) and optical spectrum in vacuum ultra-violet region. The result of XPS that the energy gap of La2O3 films is 5.18±0.2 eV, the result is confirmed by the optical spectrum which reveals that the value of the Eg is 5.20 eV.XPS can be used to determine the band alignment. According to XPS measurements, the VBO and CBO of La2O3 to Si are determined to be 2.43±0.1 and 1.66±0.1eV. The results show the corresponding larger VBO value and CBO value of La2O3 to Si substrates. From the viewpoint of band alignment, those results indicate that La2O3 could be a promising candidate in the field of microelectronics as high-k material.Finally, we also Raman spectrum method was used to study the preparation of 90- nm magnetron sputtering Er2O3 thin film, and some conclusions are drawn, prove that this method can be applied in the research of rare earth oxide microstructure.