GROWTH OF AMORPHOUS AND EPITAXIAL ALTERNATIVE GATE DIELECTRICS ON SILICON BY MOLECULAR-BEAM EPITAXY AND THEIR CHARACTERIZATION

Open Access
Author:
Edge, Lisa Friedman
Graduate Program:
Materials Science and Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 27, 2006
Committee Members:
  • Darrell G Schlom, Committee Chair
  • Elizabeth C Dickey, Committee Member
  • Venkatraman Gopalan, Committee Member
  • Thomas Nelson Jackson, Committee Member
Keywords:
  • high-K
  • molecular-beam epitaxy
  • LaAlO3
  • LaScO3
  • Sc2O3
  • La2O3
  • molecular-beam deposition
  • alternative gate dielectrics
Abstract:
The continued scaling of SiO2 in metal-oxide-semiconductor field-effect transistors (MOSFETs) is approaching its fundamental limit and in the next few years will have to be replaced with an alternative gate dielectric if Moore’s law is to continue. In a search for suitable alternative dielectrics, I have investigated the growth of amorphous and epitaxial LaAlO3, LaScO3, La2O3, and Sc2O3 thin films by molecular-beam epitaxy (MBE) on silicon. A major challenge in the growth of alternative gate dielectrics on silicon is the formation of SiO2 at the interface between silicon and the high-K gate dielectric. In this dissertation, I have established deposition conditions that yielded abrupt interfaces (< 0.1 Å of SiO2) between amorphous LaAlO3 or LaScO3 thin films and silicon. These results demonstrate the thinnest gate dielectrics ever produced that are free of interfacial SiO2, despite exposure to air. The thermal stability between silicon and the abrupt amorphous LaAlO3 and LaScO3 thin films was established for the first time. By 900 °C, crystallization is clearly observed, but the LaAlO3/Si interface remains sharp with no detectable interfacial SiO2. The thermal stability results establish key processing windows for the integration of amorphous LaAlO3 and LaScO3 thin films into silicon-based MOSFETs. In this work, the following critical physical properties of amorphous LaAlO3 thin films deposited on silicon have been determined: dielectric constant (K = 16 ± 2), bandgap (Eg = 6.2 ± 0.1 eV), and band alignment (?Ec = 1.8 ± 0.2 for electrons and ?Ev = 3.2 ± 0.1 eV for holes). The following critical physical properties of amorphous LaScO3 thin films deposited on silicon have been determined: bandgap (Eg = 5.7 ± 0.1 eV) and band alignment (?Ec = 2.0 ± 0.1 eV for electrons and ?Ev = 3.1 ± 0.1 eV for holes). In this dissertation, epitaxial (0001) La2O3 thin films with the hexagonal crystal structure were grown on (111) Si for the first time. Epitaxial Sc2O3 thin films were grown directly on (111) Si with the following orientation relationship (111) Sc2O3 // (111) Si and [1-10] Sc2O3 // [-110] Si (B-type epitaxy). The epitaxial Sc2O3/Si interface was also prepared to be free of SiO2 and single-domain (free of in-plane rotational twinning).