**2. Formation of sol-gel-derived HfO2 on Si(001) wafers fired in air**

A Hitachi HF-3000 transmission electron microscope (HRTEM) equipped with a cold type field-emission-gun (C-FEG) was used to obtain cross-sectional views of HfO2 films on Si(001) wafers fired at 450 oC (amorphous state) and 700 oC (crystallized) [Figure 1 (a) and 1(b)]. The film fired at 700 oC did not show Moire patterns, indicating that the film consisted of single-crystal grains. Some subgrain boundaries or defects such as dislocations and twins were present, so overall the HfO2 film fired at 700 oC was poly-crystalline.

Sol-gel-derived HfO2 films on Si(001) wafers were evaluated by X-ray photoelectron spectroscopy (XPS). The XPS spectra of the Hf 4f [Figure 2(a)] and O 1s emissions [Figure 2(b)]

HfO2 and ZrO2 thin films are the most promising candidates as alternative high permittivity (high-*k*) oxides for replacing the SiO2 gate dielectric material used in CMOS devices (Gusev, 2005, Wilk et al., 2001). Because of the higher permittivity, the dielectric gate insulator thickness can be increased for a given capacitance, resulting in reduced tunneling leakage current. HfO2 has promising properties such as high permittivity (25~40) (Oniki et al. 2009, Wilk et al., 2000, 2001), a conduction band offset as high as 1.5 eV (Lucovsky, 2002), and a

In device fabrication processes, HfO2 and ZrO2 thin film layers are deposited by chemical vapor deposition (CVD) or physical vapor deposition (PVD) or sputtered onto Si substrates (Gao et al., 2000, Wang et al., 2005) using argon (Ar) and O2 mixed gases. A sol-gel process offers various advantages for fabricating ZrO2, HfO2, ZrO2–Y2O3 (YANG, 1996) and HfO2 – Y2O3 (Nishide et al., 2000) thin films. The properties of a sol-gel-derived thin film depend on the composition of the sol solution, and residual H2O may affect the performance of the film. Investigations of the basic structural and optical properties of sol-gel-derived HfO2 films have shown that HfO2 films formed on quartz substrates begin to crystallize at a firing temperature of 550 oC as determined from X-ray diffraction (XRD) patterns (Nishide et al., 2000). From the interplanar spacing they derived from the XRD patterns and a comparison of their data with data from a Joint Committee on Powder Diffraction Standards (JCPDS) card, they determined the crystalline phase of the sol-gel-derived HfO2 film to be monoclinic. Recently, on the basis of high-resolution transmission electron microscopy (HRTEM) measurements in combination with results of electron beam nanodiffraction analyses, sol-gel-derived HfO2 thin films on Si(001) wafers were found to crystallize in a monoclinic face-centered cubic (fcc) structure (Shimizu et al., 2004). Sol-gel-derived ZrO2 thin films fired in air at 350 and 450 °C on Si(001) wafers are reported to be amorphous and around 9-10 nm in thickness. Crystallization occurs first at 550 °C as amorphous/tetragonal (011), and finally at 700°C, the ZrO2 film crystallizes into tetragonal (011)/monoclinic (111) and (111) structures (Shimizu et al., 2009). Electrical characteristics have been evaluated using capacitors with an Al/ZrO2 and/or HfO2/Si sandwich structure. The leakage current and dielectric constant of the films have been examined using current-voltage (*I-V*) and capacitance-voltage (*C-V*) methods. On the basis of *C-V* characteristics, the dielectric constant (relative permittivity: *ε*ZrO2 and *ε*HfO2) of sol-gel derived ZrO2 and HfO2 thin films fired in air were shown to be far higher than that of silicon dioxide (SiO2: 3.9) (Shimizu et al., 2009, 2010). This chapter summarizes the characterizations of sol-gel-derived HfO2, ZrO2 and ZrO2-Y2O3 thin films on Si(001) wafers with the aim of showing their suitability as

wide band gap (~5.68 eV) (Robertson & Chen, 1999, Robertson, 2000).

alternative gate insulator materials in advanced CMOS devices.

**2. Formation of sol-gel-derived HfO2 on Si(001) wafers fired in air** 

were present, so overall the HfO2 film fired at 700 oC was poly-crystalline.

A Hitachi HF-3000 transmission electron microscope (HRTEM) equipped with a cold type field-emission-gun (C-FEG) was used to obtain cross-sectional views of HfO2 films on Si(001) wafers fired at 450 oC (amorphous state) and 700 oC (crystallized) [Figure 1 (a) and 1(b)]. The film fired at 700 oC did not show Moire patterns, indicating that the film consisted of single-crystal grains. Some subgrain boundaries or defects such as dislocations and twins

Sol-gel-derived HfO2 films on Si(001) wafers were evaluated by X-ray photoelectron spectroscopy (XPS). The XPS spectra of the Hf 4f [Figure 2(a)] and O 1s emissions [Figure 2(b)]
