**4. Crystallinity of sol-gel-derived HfO2 thin films on Si(001) wafers**

The XRD patterns for HfO2 films on Si(001) wafers fired at 450, 550 and 700 oC were found to be in good agreement with previously reported results (Nishide et al., 2000) by using a spectrometer (Rigaku RAD-2 XRD) with CuKαradiation (Figure 4). Specifically, the film was still amorphous at 450 oC, and at 550 oC, new peaks appeared at 2θ = 28.4 and 31.8°, as well as small peaks in the region from 18 to 41°; these have been assigned to monoclinic crystalline HfO2 components (Nishide et al., 2000). At 700 oC, the HfO2 film was completely crystallized.

Fig. 4. XRD patterns obtained for HfO2 films on Si(001) wafers fired at 450, 550 and 700 oC. Open circles indicate monoclinic HfO2 (Shimizu et al., 2004).

In the electron beam (EB) nanodiffraction pattern for a cross section of the HfO2 film fired at 550 oC, the Debye ring indicates the beginning of crystallization [Figure 5(a) and 5(b)].

Characterization of Sol-Gel-Derived and Crystallized

(Shimizu et al., 2004).

interplanar spacing (Shimizu et al., 2004).

HfO2, ZrO2, ZrO2-Y2O3 Thin Films on Si(001) Wafers with High Dielectric Constant 321

Fig. 6. Electron beam nanodiffraction patterns: (a) diffracted pattern on (110) plane of Si crystal and (b) schematic diffraction spots. *r* is the distance between diffracted spots in (111), (220) and (004) in the diamond structure and *d* is the corresponding interplanar spacing

Fig. 7. Electron beam nanodiffraction patterns: (a) diffracted pattern from a cross section of the HfO2 film sintered at 700 oC and (b) schematic of the diffraction spots. *r* is the distance between diffracted spots in (111) and (220) in the HfO2 film and *d* is the corresponding

Le=542 mm, λ=0.001969 nm at 300 KV, spot size=1.0 nm (Debye ring: r1=3.7 mm d1=0.288 nm)

Fig. 5. Electron beam nanodiffraction pattern for the (110) plane of the HfO2 film fired at 550 oC. *r* is the distance between diffracted spots in (111) in the HfO2 film and *d* is the corresponding interplanar spacing (Shimizu et al., 2004).

The crystalline structure of the sample fired at 700 oC was determined by analyzing the EB nanodiffraction patterns as follows. First, the camera length (Le) of the HRTEM was determined on the basis of the EB nanodiffraction pattern for a cross section of the Si (110) substrate [Figure 6(a)] and the assignment of the diffraction spots [Figure 6(b)]. Using the data for Si from the International Centre for Diffraction Data, the camera length of the HRTEM was determined to be 542 mm (Shimizu et al., 2004).

Based on the EB nanodiffraction pattern for the sample fired at 700 oC [Figure 7(a)], the distances (*r*) between spots in the electron diffraction pattern appearing on the microscopic film were *r*1 = 3.7 mm, *r*2 = 3.4 mm and *r*3 = 6.9 mm for the (111), (111) and (220) planes, respectively [Figure 7(b)]. The corresponding interplanar spacings were determined to be *d*1 = 0.288 nm, *d*2 = 0.314 nm and *d*3 = 0.181 nm using the camera length. A detailed analysis of the alignment of the nanodiffraction spots, with the (000) spot at the center surrounded by 4 (111) spots and 2 (220) spots, together with the interplanar spacings, revealed that the HfO2 film sintered at 700 oC had a monoclinic fcc (face centered cubic) structure. One of the measured interplanar spacings of the crystalline HfO2 was 0.314 nm, which is in good agreement with the spacing of the Si (111) planes. This implies the possibility of the epitaxial growth of HfO2 films on the Si (111) surface (Shimizu et al., 2004).

(000)

Fig. 5. Electron beam nanodiffraction pattern for the (110) plane of the HfO2 film fired at 550 oC. *r* is the distance between diffracted spots in (111) in the HfO2 film and *d* is the

The crystalline structure of the sample fired at 700 oC was determined by analyzing the EB nanodiffraction patterns as follows. First, the camera length (Le) of the HRTEM was determined on the basis of the EB nanodiffraction pattern for a cross section of the Si (110) substrate [Figure 6(a)] and the assignment of the diffraction spots [Figure 6(b)]. Using the data for Si from the International Centre for Diffraction Data, the camera length of the

**(a) (b)** 

Based on the EB nanodiffraction pattern for the sample fired at 700 oC [Figure 7(a)], the distances (*r*) between spots in the electron diffraction pattern appearing on the microscopic film were *r*1 = 3.7 mm, *r*2 = 3.4 mm and *r*3 = 6.9 mm for the (111), (111) and (220) planes, respectively [Figure 7(b)]. The corresponding interplanar spacings were determined to be *d*1 = 0.288 nm, *d*2 = 0.314 nm and *d*3 = 0.181 nm using the camera length. A detailed analysis of the alignment of the nanodiffraction spots, with the (000) spot at the center surrounded by 4 (111) spots and 2 (220) spots, together with the interplanar spacings, revealed that the HfO2 film sintered at 700 oC had a monoclinic fcc (face centered cubic) structure. One of the measured interplanar spacings of the crystalline HfO2 was 0.314 nm, which is in good agreement with the spacing of the Si (111) planes. This implies the possibility of the epitaxial growth of HfO2 films on the Si (111) surface (Shimizu et al.,

Le=542 mm, λ=0.001969 nm at 300 KV, spot size=1.0 nm

corresponding interplanar spacing (Shimizu et al., 2004).

HRTEM was determined to be 542 mm (Shimizu et al., 2004).

(Debye ring: r1=3.7 mm d1=0.288 nm)

2004).

Fig. 6. Electron beam nanodiffraction patterns: (a) diffracted pattern on (110) plane of Si crystal and (b) schematic diffraction spots. *r* is the distance between diffracted spots in (111), (220) and (004) in the diamond structure and *d* is the corresponding interplanar spacing (Shimizu et al., 2004).

Fig. 7. Electron beam nanodiffraction patterns: (a) diffracted pattern from a cross section of the HfO2 film sintered at 700 oC and (b) schematic of the diffraction spots. *r* is the distance between diffracted spots in (111) and (220) in the HfO2 film and *d* is the corresponding interplanar spacing (Shimizu et al., 2004).

Characterization of Sol-Gel-Derived and Crystallized

sites in the films (Hirashita et al., 1993).

are attributed to the adsorption of

order reaction (Nishide et al., 2004).

and thin films of ceramics and semiconductors.

Hf-OH bonds at nanopore sites in the HfO2 films.

**5.2 TPD spectral analyses of sol-gel-derived HfO2 thin films** 

HfO2, ZrO2, ZrO2-Y2O3 Thin Films on Si(001) Wafers with High Dielectric Constant 323

TPD curves can be obtained for various *m*/*z*'s with increasing temperature, thereby enabling quantitative identification of species desorped from materials and films. Simultaneously, the desorped species can be physically and chemically analyzed. In addition, reaction rate analyses of desorped gases can be performed. Figure 8 shows examples of (a) a nonsymmetrical TPD curve indicated by the solid line (the first-order reaction) and (b) a symmetrical TPD curve indicated by the dashed line (the second-order reaction) as a function of temperature. The arrow on the nonsymmetrical TPD curve corresponds to the evolution of physisorbed and chemisorbed H2O, which is specified to be a liquid such as water and water molecules hydrogen-bonded to Si-OH bonds at nanopore

For chemical-vapor-deposited SiO2 films, three distinct H2O desorption states have been defined (Hirashita et al., 1993). They are physisorbed H2O evolved at temperatures between 100 and 200 °C and chemisorbed H2O evolved at temperatures between 150 and 300 °C in a TPD measurement. The higher desorption peak between 350 and 650 °C is ascribed to Si-OH bonds formed during film growth. Thus, TPD is a useful technique for evaluating surfaces

The desorption of H2O (*m*/*z* = 18) that evolved from sol-gel-derived HfO2 films on Si was analyzed by TPD (Figure 9). The HfO2 films were fired at 450, 550, and 700 °C for 30 min. The vertical axis indicates the current value of QMS. The small peaks below 200 oC are due to the physisorbed H2O (mere adsorption of H2O) on the surface of the HfO2 films and/or chemisorbed Hf-OH in the bulk at the surface area. Based on experiments, the small peaks

H2O immediately after the samples were taken out of the furnace and the amount of desorbed water (i.e., adsorbed water) saturated. The desorption states of physisorbed H2O and/or chemisorbed Hf-OH bonds originate from liquid-like water, water molecules, and

Regarding the major peaks in the TPD spectra, two types of desorption curves are observed at temperatures higher than 200 °C. One has the form of a symmetrically shaped peak (Lorentzian distribution shoulder as shown by the dashed line) at around 320 °C (fired at 450 °C), which is reaction-controlled (Soraru, 2002) (the second-order reaction) (Nishide et al. 2004). The other consists of nonsymmetrical peaks at approximately 420 °C (fired at 550 °C) and 480 °C (fired at 700 °C) which are diffusion-controlled (the first order reaction) (Nishide et al., 2004). When the curve is symmetrical in shape, the peak at around 320 °C (fired at 450 °C) is not caused by physisorbed H2O from the nanopores at the surface area, but can be ascribed to the associated desorption of chemisorbed water (Hf-OH) from the gel film, resulting in the formation of H2O during firing, which is specified to be the second-

For the samples fired at 450 °C, Hf-OH bonds in the HfO2 film bulk convert to HfO2 and/or H2O during heating and the resulting H2O contributes to the major desorption peak in the

≡ Hf-OH HO-Hf ≡ → ≡ Hf-O-Hf ≡ +H2O. (1)

TPD curve [Figure 10(a) and 10(b)], as a result of the following reaction
