Silicon-based High-¦Ê Materials, Molecular Beam Epitaxy

For continued technology scaling, high k materials are required to replace SiO₂ as gate dielectric in the next generation metal oxide field effect transistors (MOSFET). Two kinds of materials are most promising. One is Group IVB metal oxides such as HfO₂ and ZrO₂; the other is Group IIIA and Group IIIB metal oxides including Al₂O₃, Y₂O₃ and some other rare earth oxides. In this thesis, we have studied the growth and characterization of high k materials HfO₂ and Er₂O₃.Here, the first two chapters introduce the research background and experimental equipments.In Chapter 3, the MBE growth and characterization of HfO₂ films are discussed. HfO₂ films were grown by electron beam evaporation using a metallic Hf source. Firstly, the basic physical and chemical properties of the as-grown films were characterized by using the corresponding methods. The as-deposited films are stoichiometric and polycrystalline, as verified by X-ray spectroscopy (XPS) and transmission electron microscopy (TEM) results, respectively. Atomic force microscopy (AFM) images show an extremely smooth surface obtained, with a root-mean-square (rms) roughness of about 0.16 nm for a 12 nm thick HfO₂ film. The films exhibit the overall dielectric constant of 18.Chapter 4 includes the following four sections. Firstly, the thermal stability of HfO₂ films on Si substrates. For the HfO₂ films upon rapid temperature annealing (RTA) at 900℃ in 1 atm N₂ for 30 s, both scan electron microscopy (SEM) and AFM results show a flat surface, and no voids or pits are found, indicating a good thermal stability of HfO₂ films upon annealing in the N₂ ambient. However, HfO₂ films begin to decompose at about 750℃ under the ultrahigh vacuum (UHV) condition, as verified by synchrotron radiation photoemission spectroscopy (SRPES) results. Secondly, band offset of HfO₂ films on Si(001). The photoemission based method proposed by Kraut et al. is used to determine the band offset of HfO₂ with Si. Accordingly, the valence band offset of HfO₂ with Si is 3.46 eV. Thirdly, the band gap of HfO₂. By using the O 1s energy loss spectrum, the band gap of HfO₂ films is roughly measured to be about 5.0 eV. The relatively small value obtained mainly arises from the lower energy resolution due to the non-monochromatic Mg ka x-ray used. The last section concerns in situ photoemission study on initial growth of HfO₂ films on Si(001) is also included in Chapter 4. Interfacial layers between HfO₂ and the Si substrate are observed even for very thin HfO₂ films and confirmed to be Si-rich...