Growth and characterization of hafnium oxide for future transistor gate dielectrics

During the period of this thesis (1998–2003), there has been a growing effort by researchers to identify a high permittivity dielectric to replace SiO₂ in the transistor (Si MOSFET) gate stack of future nano-electronic devices. Developing a fundamental understanding of physical and chemical properties of the gate stack, and their relation to MOSFET electrical behavior is critical if high-K materials are to be integrated. The studies done within the framework of this thesis aim to address or contribute towards these efforts.; High-quality, ultra-thin films of HfO₂ are deposited on Si(100) using a simple thermal chemical vapor deposition (CVD) process, and studied by a variety of techniques. The films display structural, physical and electrical properties appropriate for use as a gate oxide. Films are stable with respect to reaction with the substrate at temperatures as high as 1000C. Films with an equivalent oxide thickness of 11Å were produced using this CVD technique, while still exhibiting low leakage currents.; The thermal decomposition behavior of the HfO₂/SiO₂/Si gate stack in a reducing environment is investigated. The decomposition time is found to be strongly dependent on the HfO₂ film thickness, but appears nearly independent of the SiO₂ bottom layer thicknesses. The sequence of events (during decomposition) as a function of time and temperature are discussed.; Combined photoemission and inverse photoemission studies are employed to study the band alignment of HfO₂ on silicon. It is found that HfO₂ is a viable dielectric from a band alignment perspective, satisfying the minimum barrier height requirements. The presence, energy and spatial location of charge present in the films are also discussed.; Photoemission and inverse photoemission spectroscopic studies on HfO ₂/Hf and HfO₂/Pt systems are reported. It is found that the effective workfunction of metals are different than their vacuum workfunctions and that Hf and Pt metals when in contact with HfO₂ are suitable metals for NMOS and PMOS applications respectively from a work function perspective. The results obtained are consistent with the electrical measurements reported here and elsewhere. The electronic alignment can be rationalized within charge neutrality based models of interface dipole formation.