Thin Film Analysis of Material and Discussion

Fig. 3-11 shows the FTIR spectra of HfO2 films after various post-treatments, including Baking-only, H2O vapor and 3000 psi-SCCO2 treatment. The functional group referred to Hf-O-Hf bonding is at 509 cm^-1 and 690 cm^-1, and the absorption peak at around 1070 cm^-1 attributes to the Si-O-Si bond. The Si-O-Si bond originates form the formation of interface layer (SiOx) between HfO2 film and silicon wafer during fabricating HfO2 films in Ar/O2 ambient. The peak intensity of Si-O-Si bond for different treatments is almost the same, meaning that these post-treatments would not make different influence on the thickness and quality of the interfacial SiOx film.

For the H2O-vapor-treated HfO2 film, however, the peak intensity of Hf-O-Hf bands (509 cm^-1 and 690 cm^-1) raises apparently in comparison with the baking-only-treated HfO2 film. This is believed well that the H2O vapor would permeate into HfO2 film and makes reaction with Hf dangling bonds (i.e. traps) forming Hf-O-Hf bands. These traps in the low-temperature deposited HfO2 film could be thereby passivated by H2O vapor molecules. Furthermore, with 3000 psi- SCCO2 treatment, obvious increase in the intensity of Hf-O-Hf bonding is observed in the FTIR. It indicates that the best transport efficiency of H2O molecules into HfO2 film is achieved by the SCCO2 fluids, potentially modifying the dielectric properties of HfO2 film, and the transporting

mechanism for SCCO2 fluids taking H2O molecule into HfO2 film is shown in Fig.

3-12.

3.2.2 Thermal Desorption System – Atmospheric Pressure Ionization Mass Spectrometer (TDS-APIMS) Analysis

The TDS measurement, as shown in the Fig. 3-13, was carried out upon heating these treated HfO2 films from 50 to 800 °C at a heating rate of 10 °C/min in vacuum (10⁻⁵ Pa.). In Fig. 3-13 (a), m/e (mass-to-charge ratio) = 32 peak that is attributed to O2 was monitored to evaluate the content of oxygen outgassing form HfO2 films. It is clearly found the highest oxygen content is detected in the 3000 psi-SCCO2 treated HfO2 film, certainly consistent with the FTIR observation. From Fig. 3-13 (b), m/e (mass-to- charge ratio) = 44 peak that is attributed to CO2, the residual carbon dioxide in HfO2 is equal after various post-treatments. This is result from SCCO2 fluid not only employed to transport the CO2 molecule into HfO2 film but the CO2 molecule is not remain in addition [21, 22].

3.2.3 X-ray Photoelectron Spectroscopy (XPS) Analysis

XPS involves measuring the photoelectron spectra obtained when a sample surface is irradiated with x-rays. The kinetic energy (peak position) of the photoelectrons can be written as

φ φ ν -E - -q h

E_K = _{B s} (3.12) where h is the x-ray energy, Eν B is the binding energy (the difference between the Fermi level and the energy level being measured), φ_s is the work function of the electron spectrometer, q is the electronic charge, and φ is the surface potential.

We have also performed XPS measurements using an Al Kα X-ray source

Figure 3-14 shows the O 1s core level peaks also demonstrated binding energy shift with changing of different post-treatments. Each peak can be split into two sub-peaks by Gaussian fitting which represent the Hf-O bonding at ~530.1 eV and O-Si bonding at ~531.5 eV [59,60]. The peak intensity of O-Si bond for different treatments is almost the same, meaning that these post-treatments would not make different influence on the thickness and quality of the interfacial SiOx film. For the H2O-vapor-treated HfO2 film, however, the peak intensity of Hf-O bands raises apparently in comparison with the baking-only-treated HfO2 film. This is believed well that the H2O vapor would permeate into HfO2 film and makes reaction with Hf dangling bonds (i.e. traps) forming Hf-O bands. These traps in the low-temperature deposited HfO2 film could be thereby passivated by H2O vapor molecules.

Furthermore, with SCCO2 treatment, obvious increase in the intensity of Hf-O bonding is observed in the XPS. It indicates that the best transport efficiency of H2O molecules into HfO2 film is achieved by the SCCO2 fluids, potentially modifying the dielectric properties of HfO2 film, and the transporting mechanism for SCCO2 fluids taking H2O molecule into HfO2 film is shown in Fig. 3-12.

3.2.4 Transmission Electron Microscopy (TEM) Analysis

Figure 3-15 (a), (b), (c) show the influence of various post-treatments on HfO2

thin film samples in TEM material analysis. The first group labeled as Baking-only treatment, was designed as the control sample, and was only baked on a hot plate at 150 °C for 2 hrs. The second group labeled as H2O vapor treatment, was immersed into a pure H2O vapor ambience at 150 °C for 2 hrs in a pressure-proof stainless steel chamber with a volume of 100cm³. The third group marked as 3000psi-SCCO2

treatment, was placed in the supercritical fluid system at 150°C for 2 hrs, where was

injected with 3000psi of SCCO2 fluids mixed with 5 vol.% of propyl alcohol and 5 vol.% of pure H2O. The interfacial layer of SiOX for different treatments is almost the same. It is found that 3000psi-SCCO2 treatment can improve performance of MIS, including leakage current density suppression and EOT reduction. On the other hand, the k value of Baking-only-treated, H2O-vapor-treated and 3000psi-SCCO2-treated HfO2 film is about 20.4, 24.8 and 29.4. The k value is increased and interfacial layer is almost the same. It can be understood reasonably that during 3000psi-SCCO2- treated HfO2 film is dense and thickness of interfacial layer is increasing a little due to oxygen penetration. The detail discussion would be in 3.1.3.