Shinji Ishidzuka

Si(001) Surface Layer-by-Layer Oxidation Studied by Real-Time Photoelectron Spectroscopy using Synchrotron Radiation

High-resolution O 1s and Si 2p photoelectron spectroscopy using synchrotron radiation was employed to clarify a layer-by-layer oxidation reaction mechanism on a Si(001) surface from the viewpoint of point defect generation due to an oxidation-induced strain at a SiO2/Si interface. The Siβ and Siα components in Si 2p3/2 spectra, which are assigned to the first and second strained Si layers, respectively, below the transition layer composed of suboxides, Si1+, Si2+, and Si3+, significantly decrease during the step-by-step temperature increase-enhanced growth of the second oxide layer. Because of the corresponding band bending changes measured using the O 1s peak position, which are caused by defect-related band gap states, the observed decreases in Siβ and Siα components, indicating a decrease in interfacial strain, are induced not only by the structural relaxation of a SiO2 network due to a thermal annealing effect, but also due to the generation of point defects at the SiO2/Si interface. Continuous band bending changes with the growth of the third oxide layer also suggest that the point defects are generated during oxide growth, whereas the Siβ and Siα components are maintained almost constant. On the basis of the observed interfacial strain and point defect generation changes, the layer-by-layer growth kinetics of the first, second and third oxide layers is discussed using a unified Si oxidation reaction model mediated by point defect generation at the SiO2/Si interface [S. Ogawa and Y. Takakuwa: Jpn. J. Appl. Phys. 45 (2006) 7063].

Graphene Growth and Carbon Diffusion Process during Vacuum Heating on Cu(111)/Al2O3 Substrates

In this study, the behavior of carbon atoms in the annealing/cooling process of graphene/Cu(111) substrates is investigated using photoelectron spectroscopy and secondary ion mass spectroscopy. After the growth of graphene on Cu(111) surfaces, Cu2O was formed at the graphene/Cu interface during transportation through air atmosphere. The Cu2O layer completely disappeared by vacuum annealing at 500 °C. Graphene was decomposed and carbon atoms diffused into the Cu substrate by further elevation of annealing temperature to 950 °C. When the sample was cooled down, the carbon atoms did not segregate on the surface and remained in the Cu substrate. This result indicates the carbon atoms easily diffuse into Cu substrates in vacuum annealing while the amount of diffused carbon atoms in the thermal chemical vapor deposition (CVD) process is smaller, suggesting that the barrier layer, which prevents the diffusion of C atoms, exists on Cu surfaces in the graphene CVD growth.

Time-Resolved Photoelectron Spectroscopy of Oxidation on the Ti(0001) Surface

High-resolution photoelectron spectroscopy using synchrotron radiation was applied for monitoring in real time the oxidation kinetics on the Ti(0001) surface at 405 C with dry O{sub 2} gas. The time evolution of O 1s photoelectron intensity showed a linear uptake curve up to {approx}90 L followed by a sudden saturation up to {approx}160 L and then a restart of the linear increase, indicating that O{sub 2} adsorption obeys a zero-order reaction scheme before and after the saturation. Corresponding to the first linear uptake and saturation, the surface core level shift (SCLS) component of Ti 2p decreased predominantly and disappeared completely, and appeared again after the saturation and remained persistently during TiO{sub 2} growth. Thus the zero-order reaction of O{sub 2} adsorption on the Ti(0001) surface at 405 C is concerned with the metallic Ti layer on the outermost surface.

Relation Between Oxidation Rate and Oxidation-Induced Strain at SiO2/Si(001) Interfaces during Thermal Oxidation

To experimentally verify the Si oxidation reaction model mediated by point defect (emitted Si atoms and their vacancies) generation due to oxidation-induced strain, real-time photoelectron spectroscopy using synchrotron radiation was employed to simultaneously evaluate the amount of oxidation-induced strained Si atoms at the SiO2/Si interface, oxidation state, and oxidation rate during oxidation on n-type Si(001) surfaces with O2 gas. It is found that both the oxidation rate and the amount of strained Si atoms at the completion of the first-oxide-layer growth decrease gradually with increasing temperature from 300 to 550 °C, where the oxide grows in the Langmuir-type adsorption manner. It is found that the interface strain and oxidation rate have a strong correlation. We discuss the reason for the oxide coverage and oxidation temperature dependences of interfacial strain from the viewpoint of the behavior of adsorbed oxygen during the first-oxide-layer growth.

Enhancement of SiO2/Si(001) interfacial oxidation induced by thermal strain during rapid thermal oxidation

Rapid thermal oxidation, in which samples are intensely heated to a preset temperature, is used to grow silicon oxide on Si substrates while avoiding significant diffusion of impurities into the substrate. In previously proposed reaction models for rapid thermal oxidation, the oxidation rate is only determined by the temperature and O2 pressure. Therefore, it is believed that the rate of oxidation at a preset temperature is independent of the initial substrate temperature. In this study, the interfacial oxidation reactions that follow Si(001) surface oxidation were observed using real-time Auger electron spectroscopy. Interfacial oxidation was enhanced when the substrate temperature was increased from temperature T1 to temperature T2 at the end of Si(001) surface oxidation. As a result, strong T1 and T2 dependences of the interfacial oxidation rate were observed. The interfacial oxidation rate at T1 = room temperature was more than 10 times higher than that at T1 = 561 °C, even for the same T2 (682 °C). A...