Er <sub> 2 </ Sub> O <sub> 3 </ Sub> High-k Gate Dielectric Materials, Molecular Beam Epitaxial Growth, Structure And Physical Properties

The industry's demand for higher integrated circuit density and performance has forced the gate dielectric layer thickness to decrease rapidly. As a consequence, static leakage power due to direct tunneling through the gate oxide has been increasing at an exponential rate. The use of conventional SiO₂ films as gate oxide is reaching its limit due to the rapid increase in tunneling current. Therefore, a variety of alternative high-k materials are being investigated as possible replacements for SiO₂. The higher dielectric constants in these materials allow the use of physically thicker films, potentially reducing the tunneling current while maintaining the gate capacitance needed for scaled device operation.In recent years, many kinds of high-k materials such as HfO₂, Y₂O₃ and Pr₂O₃, have been widely studied as potential replacements of SiO₂ layer in CMOS devices. It has been reported that Er₂O₃ may be one of the most promising alternative dielectrics. However, the Er₂O₃ films epitaxially grown on Si and their properties have not been reported. In this thesis, we have studied the growth and characterization of high k Er₂O₃ films on Si substrates.The epitaxial growth of Er₂O₃ films on Si(001) and Si(111) have been investigated. The epitaxial relationship between Er₂O₃ and Si(001) substrate is as follows: Er₂O₃(110) // Si(001), Er₂O₃[001]//Si[110] or Er₂O₃[110] // Si[110]. The epitaxial relationship between Er₂O₃ and Si(111) is Er₂O₃(111)//Si(111). ErSi₂ silicide is found apparently in the films grown at lower temperatures and/or in lower oxygen ambient pressures. Both the effects of oxygen pressure and growth temperature on epitaxial growth of Er₂O₃ on Si(001) substrates are discussed based on the possible chemical reactions. In addition, the oxidized Si surface can also suppress the formation of the silicide phase. The surface roughness and crystallinity of the Er₂O₃ films grown on oxidized Si (111) and Si (001) surfaces are improved as compared to those grown on the clean Si surfaces.The experimental data on band alignments of high-k Er₂O₃ films epitaxially grown on Si substrates are obtained. By using x-ray photoelectron spectroscopy, the valence and the conduction band offset of Er₂O₃ to Si are determined to be 3.1± 0.1eV and 3.5±0.3eV, respectively, showing a roughly symmetrical offset at the conduction and the valence band. And the energy gap of Er₂O₃ is determined to be 7.6 ±0.3eV. From the band offset viewpoint, those obtained numbers indicate that Er₂O₃ could be a promising candidate for high-k gate dielectrics.In order to investigate the interface of Er₂O₃, synchrotron radiation photoemission spectroscopy was used to study the intial growth of Er₂O₃ films on Si at O₂ pressures of 7×10^-6 Torr. Because the occurrence of interface layers such as SiO_x and silicate at the atternative high k dielectric / Si is a major issure, which may lower the overall dielectric constant. In our experiments, an interface layer was observed enen for a very thin Er₂O₃ film at a very low temperature (room temerature), which is supposed to attributed to the effect of the Er atom catalytic oxidation effect.In this letter, we also studied the FN tunneling of holes in metal/Er₂O₃/ p-Si structures. The advent of FN tunneling is a fundamental process in the description of current-voltage characteristic of a metal/dielectric/semiconductor structure. At large fields, the carriers may tunnel through the forbidden region of the insulator into the allowed states of insulator. And we confirmed occurrence of FN hole tunneling in metal/Er₂O₃ p-Si capacitor structures. The effective mass for holes in the oxide is found to be 0.05m, where m is the free electron mass.