High-κ Complex Oxides for Advanced Gate Dielectric Applications Grown by Atomic Layer Deposition

  • Author / Creator
    Ahadi, Kaveh
  • As conventional SiO2 gate dielectric thickness shrank to a few atomic layers, gate dielectric tunneling increased dramatically. The primary way to reduce tunneling is to increase film thickness, which decreases capacitance. High-dielectric-constant (high-κ) oxides were introduced to maintain capacitance density while film thickness was increased. A reliable interface between the high-κ oxide and semiconductor is crucial for good transistor performance. High-κ oxides suffer from lower carrier mobility, degraded reliability and threshold voltage instability compared to silicon dioxide. High-κ binary oxides (HfO2, ZrO2 and Al2O3) have been have been studied extensively for high-κ gate dielectric applications. Complex oxides offer a higher degree of flexibility to tackle the major shortcoming of high-κ oxides. In this work, hafnium zirconate, hafnium aluminate and zirconium aluminate thin films were grown on silicon, gallium nitride and indium phosphide for advanced gate dielectric applications using plasma enhanced atomic layer deposition. Metal-oxide-semiconductor capacitor devices were fabricated to study dielectric properties, device performance and semiconductor-gate dielectric interfacial quality. All the devices revealed very low density of interfacial traps and small capacitance-voltage hysteresis. Hafnium zirconate had the best performance with ultra-low Dit of 2.61x1010 cm-2 eV-1 on silicon and 8.62x1011 cm-2 eV-1 on indium phosphide mainly due to the combination of low growth substrate temperature (100°C) and high post-fabrication heat treatment temperature (510°C). Furthermore, very low density of interfacial traps proved that there was a reliable interface between the high-κ complex oxide and the semiconductor. The hafnium zirconate dielectric also had the highest capacitance density and lowest leakage current. The leakage current was dominated by direct tunneling in hafnium zirconate. The conduction and valence band offsets of the hafnium zirconate gate dielectrics on InP were measured and compared to pure zirconia using an x-ray photoelectron spectroscopy method. Hafnium zirconate structures showed wider band gap and larger conduction band offset but smaller valence band offset compared to pure zirconia. This was attributed to the increase in valence band width with hafnia addition, which in turn reduced the hafnium zirconate gate dielectric’s valence band offset. The band structure line-up is type I with band offsets of 3.53 eV for electrons and 1.03 eV for holes in Hf0.25Zr0.75O2/InP heterojunctions.

  • Subjects / Keywords
  • Graduation date
    Spring 2016
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.