**8.4 TPD analyses of sol-gel-derived ZrO2-Y2O3 thin films**

TPD was used to investigate the desorption of H2O (*m*/*z* = 18) that evolved from sol-gelderived ZrO2-Y2O3 thin films on Si(001) wafers, which were fired at 350 and 700 °C for 30 min (Figure 30). The vertical axis indicates the current value of QMS. The film thicknesses were 11.1 and 6.9 nm, respectively. The intensity of the TPD curves decreased as the firing temperature increased, indicating that the amount of H2O was reduced in the ZrO2-Y2O3 thin films on Si(001) wafers. For the ZrO2-Y2O3 thin film fired at 350 oC, the peaks seen at 370 and 400 oC are attributed to equipment noise.

Two TPD curves are close to those of ZrO2 thin films (Shimizu & Nishide, 2011), except that the sample fired at 350 oC does not show any similar protrusions between 100 and 200 oC like those seen for the ZrO2 thin film (Figure 22) (Shimizu et al., 2009). The peak was separated into several components using a Gaussian-type waveform (Figure 23), and the waveform indicated by the dashed line is shown as a function of temperature (Figure 30). The desorption temperature of the main peak of the ZrO2-Y2O3 thin film was approximately between 100 and 200 oC. This implies that the TPD peak may be due to physisorbed H2O (mere adsorption of H2O). In contrast, at 700 oC, the TPD curves for H2O desorption are similar in shape to that of the ZrO2 thin film. The peak from 100 to 200 oC is due to the adsorption of physisorbed H2O and the main peak at approximately 250 oC is caused by Zr-OH (chemisorbed) (Nishide et al., 2005, Takahashi & Nishide, 2004). The relative permittivity of ZrO2 formed by atomic layer deposition has been reported to be 23 (Niinisto et al., 2004).

Characterization of Sol-Gel-Derived and Crystallized

to Dr. Masanori Ikeda for his assistance with the experiments.

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**10. Acknowledgments** 

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Fig. 30. TPD curves of H2O (*m*/*z* = 18) that evolved from sol-gel-derived ZrO2-Y2O3 thin films on Si(001) wafers, which were fired at (a) 350 and (b) 700 °C for 30 min (Shimizu & Nishide, 2011)

## **9. Conclusion**

Sol-gel-derived HfO2, ZrO2 and Y doped ZrO2(ZrO2-Y2O3) thin films on Si(001) wafers fired in air between 350 and 700 °C were characterized physically, chemically and electrically with the aim of achieving alternative gate insulator materials for advanced CMOS devices. Crystallinity of the sol-gel-derived HfO2, ZrO2 films was found to be dependent on the firing temperature and sol solution. The relative permittivity of the films converged to that of bulk HfO2 and ZrO2 according to the specific sol solutions and firing temperatures. Residual H2O and OH groups in the thin films were evaluated in reference to electrical characteristics such as the leakage current of MOS capacitors. The surface of the ZrO2-Y2O3 thin films on Si(001) wafers showed less roughness than the HfO2 and ZrO2 thin films, resulting in lower leakage current in MOS capacitors. The leakage current of crystallized ZrO2-Y2O3 thin films was shown to be lower than that of the amorphous state films because of the smooth crystalline surface of the latter in comparison with the ZrO2 thin films. In conclusion, crystalline sol-gelderived ZrO2-Y2O3 thin films are postulated to be promising as alternative gate insulator materials of advanced CMOS devices.
